BACKGROUND
Quantum computing refers to the field of research related to computation systems that use quantum-mechanical phenomena to manipulate data. These quantum-mechanical phenomena, such as superposition (in which a quantum variable can simultaneously exist in multiple different states) and entanglement (in which multiple quantum variables have related states irrespective of the distance between them in space or time), do not have analogs in the world of classical computing, and thus cannot be implemented with classical computing devices.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.
FIGS. 1-4 are cross-sectional and top-down views of an example quantum dot device with trenches, in accordance with various embodiments.
FIGS. 5-7 are cross-sectional views of various examples of quantum well stacks that may be used in a quantum dot device with either trenches or fins, in accordance with various embodiments.
FIGS. 8-9 illustrate detail views of various embodiments of a doped region in a quantum dot device with either trenches or fins, in accordance with various embodiments.
FIGS. 10-12 are cross-sectional and top-down views of an example quantum dot device with fins, according to some embodiments of the present disclosure.
FIGS. 13-19 illustrate example base/fin arrangements that may be used in a quantum dot device with fins, in accordance with various embodiments.
FIG. 20 is a block diagram of an example quantum circuit assembly in which synchronized operation of control circuits may be implemented, in accordance with some embodiments.
FIGS. 21-22 are block diagrams of example control circuit assemblies to synchronize operation of control circuits in a quantum circuit assembly, in accordance with various embodiments.
FIG. 23 is a flow diagram of operating a control circuit in a quantum circuit assembly in a manner that synchronizes the control circuit with other control circuits, in accordance with some embodiments.
FIGS. 24-27 are example timing diagrams for different scenarios of synchronizing operation of control circuits in a quantum circuit assembly, in accordance with various embodiments.
FIGS. 28-29 are block diagrams of example control circuit assemblies with one or more crossbar routers to synchronize operation of control circuits in a quantum circuit assembly, in accordance with various embodiments.
FIG. 30 is a flow diagram of calibrating control circuits of a quantum circuit assembly, in accordance with some embodiments.
FIGS. 31A and 31B are top-down views of a wafer and dies that may include one or more quantum circuit assemblies disclosed herein, or portions thereof, in accordance with various embodiments.
FIG. 32 is a cross-sectional side view of a device assembly that may include one or more quantum circuit assemblies disclosed herein, in accordance with various embodiments.
FIG. 33 is a block diagram of an example quantum computing device that may include one or more quantum circuit assemblies disclosed herein, in accordance with various embodiments.
DETAILED DESCRIPTION
Overview
The systems, methods and devices of this disclosure each have several innovative aspects, no single one of which is solely responsible for all of the desirable attributes disclosed herein. Details of one or more implementations of the subject matter described in this specification are set forth in the description below and the accompanying drawings.
For purposes of illustrating synchronizing operation of control circuits in a quantum circuit assembly, proposed herein, it might be useful to first understand phenomena that may come into play in quantum computing systems. The following foundational information may be viewed as a basis from which the present disclosure may be properly explained. Such information is offered for purposes of explanation only and, accordingly, should not be construed in any way to limit the broad scope of the present disclosure and its potential applications.
As briefly described above, quantum computing, or quantum information processing, refers to the field of research related to computation systems that use quantum-mechanical phenomena to store and manipulate data. Quantum computers use so-called quantum bits, referred to as qubits (both terms “bits” and “qubits” often interchangeably refer to the values that they hold as well as to the actual devices that store the values). Similar to a bit of a classical computer, at any given time, a qubit can be either 0 or 1. However, in contrast to a bit of a classical computer, a qubit can also be 0 and 1 at the same time, which is a result of superposition of quantum states—a uniquely quantum-mechanical phenomenon. The principle of quantum superposition asserts that any two or more quantum states can be added together, i.e., superposed, to produce another valid quantum state, and that any quantum state can be represented as a sum of two or more other distinct states. Quantum entanglement is another example of a unique quantum-mechanical phenomenon. Entanglement refers to groups of particles or quantum bits being generated or made to interact in such a way that the state of one particle becomes intertwined with that of the others. Furthermore, the quantum state of each qubit cannot be described independently. Instead, the quantum state is given for the group of entangled particles as a whole. For example, two entangled qubits may be represented by a superposition of 4 quantum states, and N entangled qubits are represented by a superposition of 2N quantum states. Entanglement also contributes to the unique nature of qubits in that input data to a quantum processor can be spread out among entangled qubits, allowing manipulation of that data to be spread out as well: providing input data to one qubit results in that data being shared to other qubits with which the first qubit is entangled. Yet another example of quantum-mechanical phenomena is sometimes described as a “collapse” because it asserts that when we observe (measure) qubits, we unavoidably change their properties in that, once observed, the qubits cease to be in a state of superposition or entanglement (i.e., by trying to ascertain anything about the particles, we collapse their state) and collapse to one of the 2N quantum states.
Put simply, superposition postulates that a given qubit can be simultaneously in two states; entanglement postulates that two qubits can be related in that they are able to instantly coordinate their states irrespective of the distance between them in space and time so as to exist in a superposition of 4 states or in the case of N qubits in a superposition of 2N quantum states; and collapse postulates that when one observes a qubit, one unavoidably changes the state of the qubit and its entanglement with other qubits. These unique phenomena make manipulation of data in quantum computers significantly different from that of classical computers (i.e., computers that use phenomena of classical physics).
Another challenge that is unique to quantum computers and does not arise in classical computers resides in protecting qubits from decoherence so that they can stay in their information-holding states long enough to perform the necessary calculations and read out the results. For this reason, qubits are often operated at cryogenic temperatures, typically just a few degrees Kelvin or even just a few millikelvin above absolute zero, because at cryogenic temperatures thermal energy is low enough to not cause spurious excitations, which is thought to help minimize qubit decoherence.
The foregoing illustrates that the ability to manipulate and read out quantum states, making quantum-mechanical phenomena visible and traceable, and the ability to deal with and improve on the fragility of quantum states of a qubit present unique challenges not found in classical computers. These challenges explain why so many current efforts of the industry and the academics continue to focus on a search for new and improved physical systems whose functionality could approach that expected of theoretically designed qubits. Physical systems for implementing qubits that have been explored until now include, e.g., semiconducting qubits including those that rely on formation of quantum dots (e.g., spin qubits and charge qubits), superconducting qubits (e.g., flux qubits or transmon qubits, the latter sometimes simply referred to as “transmons”), photon polarization qubits, single trapped ion qubits, etc.
Devices implementing quantum dot qubits (referred to herein as “quantum dot devices”) are particularly promising for large-scale qubit implementation. Therefore, some descriptions of synchronizing operation of control circuits in a quantum circuit assembly are provided with reference to quantum dot devices. However, descriptions of synchronizing operation of control circuits in a quantum circuit assembly, provided herein, are also applicable to qubit devices other than quantum dot devices, such as, but not limited to, superconducting qubits, photon polarization qubits, single trapped ion qubits, etc.
In general, quantum dot devices enable formation of quantum dots to serve as quantum bits (i.e., as qubits) in a quantum circuit assembly (e.g., in a quantum computing device). Typically, a quantum circuit assembly further includes a plurality of control circuits to control the quantum dots formed in quantum dot devices to perform quantum logic operations. To that end, quantum dot devices implement multiple terminals, such as gate terminals of various types of gates (e.g., barrier gates, plunger gates, and accumulation gates), terminals for making electrical contact to provide electrical signals to one or more magnet lines configured to influence the spin states of various quantum dots, terminals for making electrical contact with doped regions of a semiconductor material (which may be referred to as “source terminals” and “drain terminals”), etc. Single electron transistor (SET) detectors, provided proximate to quantum dot qubits, may be used to detect states of various qubits. Typically, quantum dot devices include a first row of a quantum dot formation region (i.e., a row in which quantum dots may be formed) for forming quantum dots of various qubits, and a second row of a quantum dot formation region for forming quantum dots that are a part of one or more SET detectors corresponding to the qubits of the first row. Such a first row may be referred to as “active” row because quantum dots formed in this row are used as qubits for performing quantum logic operations, whereas such a second row may be referred to as a “read” row because quantum dots formed in this row are used for detecting quantum states of various quantum dots of the active row, and some quantum dot devices may include more than one active rows and/or more than one read rows. In quantum dot devices, a first plurality of terminals extend to the active row and a second plurality of terminals extend to the read row, and control circuits apply various control signals to various terminals of the active and read rows to control formation, manipulation (e.g., changing of quantum states), and readout (e.g., detection of quantum states) of quantum dots in such devices.
DC bias signals, microwave signals (e.g., signals with frequencies between about 1 and 1000 GHz), and baseband signals (e.g., signals with frequencies between about 0 and 300 MHz) are some examples of control signals applied by various control circuits to various terminals of qubit devices to control operation of such devices. Any of these signals may be applied as pulses or as continuous signals. For example, spin qubits may be controlled by sequences of microwave pulses and fast and slow square shaped voltage pulses. Control signals applied to various terminals of qubit devices represent atomic operations of quantum algorithms, quantum device calibration routines, status control and updates, state readout and detection. In various implementations, the state of the qubits could be determined by current measurements and/or by reflectometry on a charge-coupled SET device.
In general, read and write operations in a quantum circuit assembly require specific timing relation to each other. As the number of controlled qubits increases so does the amount of control channels. With thousands of control channels for gate control, qubit operation and readout, the need to partition these channels in manageable and implementable chunks increases. It also becomes clear that a single control circuit is not likely to able to implement all of the various control functions and different control channels. Therefore, new methods for quantum electronics control that can perform synchronization of various control circuits in a quantum circuit assembly are needed.
Embodiments of the present disclosure provide systems and methods for synchronizing operation of control circuits in quantum circuit assemblies. In one aspect of the present disclosure, an example control circuit assembly for controlling operation of a qubit device (e.g., a quantum dot device) may include a plurality of control circuits and an event synchronization arrangement. The plurality of control circuits may include a first and a second control circuits, configured to perform, respectively, first and second actions to control operation of the qubit device. The event synchronization arrangement may be used to control operation of the plurality of control circuits to provide to the second control circuit an indication that the first control circuit performed the first action, and to configure the second control circuit to perform the second action in response to receiving the indication that the first control circuit performed the first action. Unlike previous approaches to qubit control (e.g., qubit formation, manipulation, and readout), various embodiments of control circuit assemblies disclosed herein provide improved control over qubits, good scalability in the number of qubits included in the device, and/or design flexibility in making electrical connections to the qubits to integrate the qubit devices in larger computing devices.
In various embodiments, quantum circuit assemblies with control circuits synchronized as described herein may be implemented as components associated with a quantum integrated circuit (IC). Such components may include those that are mounted on or embedded in a quantum IC, or those connected to a quantum IC. The quantum IC may be either analog or digital and may be used in a number of applications within or associated with quantum systems, such as e.g., quantum processors, quantum amplifiers, quantum sensors, etc., depending on the components associated with the IC. The IC may be employed as part of a chipset for executing one or more related functions in a quantum system.
In order to provide substantially lossless connectivity to, from, and between the qubits, some or all of the electrically conductive portions of quantum circuit assemblies described herein, in particular various gates and conductive vias described herein, as well as other components of quantum circuits, may be made from one or more superconductive materials. However, some or all of these electrically conductive portions could be made from electrically conductive materials which are not superconductive. In the following, unless specified otherwise, reference to an electrically conductive material implies that a superconductive material can be used, and vice versa. Furthermore, materials described herein as “superconductive/superconducting materials” may refer to materials, including alloys of materials, that exhibit superconducting behavior at typical qubit operating conditions (e.g., materials which exhibit superconducting behavior at very low temperatures at which qubits typically operate), but which may or may not exhibit such behavior at higher temperatures (e.g., at room temperatures). Examples of such materials include aluminum (Al), niobium (Nb), niobium nitride (NbN), titanium nitride (TiN), niobium titanium nitride (NbTiN), indium (In), and molybdenum rhenium (MoRe), all of which are particular types of superconductors at qubit operating temperatures, as well as their alloys.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, embodiments that may be practiced. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense.
In the drawings, some schematic illustrations of cross-sectional and top-down views of example structures of various devices and assemblies described herein may be shown with precise right angles and straight lines, but it is to be understood that such schematic illustrations may not reflect real-life process limitations which may cause the features to not look so “ideal” when any of the structures described herein are examined using, e.g., scanning electron microscopy (SEM) images or transmission electron microscope (TEM) images. In such images of real structures, possible processing defects could also be visible, such as not-perfectly straight edges of materials, tapered vias or other openings, inadvertent rounding of corners or variations in thicknesses of different material layers, occasional screw, edge, or combination dislocations within the crystalline region, and/or occasional dislocation defects of single atoms or clusters of atoms. There may be other defects not listed here but that are common within the field of device fabrication.
In the following detailed description, various aspects of the illustrative implementations will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. For example, the terms “oxide,” “carbide,” “nitride,” etc. refer to compounds containing, respectively, oxygen, carbon, nitrogen, etc.; the term “high-k dielectric” refers to a material having a higher dielectric constant than silicon oxide; the term “low-k dielectric” refers to a material having a lower dielectric constant than silicon oxide. The term “insulating” means “electrically insulating,” the term “conducting” means “electrically conducting,” unless otherwise specified. Furthermore, the term “connected” may be used to describe a direct electrical or magnetic connection between the things that are connected, without any intermediary devices, while the term “coupled” may be used to describe either a direct electrical or magnetic connection between the things that are connected, or an indirect connection through one or more passive or active intermediary devices. A first component described to be electrically coupled to a second component means that the first component is in conductive contact with the second component (i.e., that a conductive pathway is provided to route electrical signals/power between the first and second components). As used herein, a “magnet line” refers to a magnetic field-generating structure to influence (e.g., change, reset, scramble, or set) the spin states of quantum dots. One example of a magnet line, as discussed herein, is a conductive pathway that is proximate to an area of quantum dot formation and selectively conductive of a current pulse that generates a magnetic field to influence a spin state of a quantum dot in the area.
Furthermore, as used herein, terms indicating what may be considered an idealized behavior, such as e.g., “lossless” (or “low-loss”) or “superconductive/superconducting,” are intended to cover functionality that may not be exactly ideal but is within acceptable margins for a given application. For example, a certain level of loss, either in terms of nonzero electrical resistance or nonzero amount of spurious two-level systems (TLSs) may be acceptable such that the resulting materials and structures may still be referred to by these “idealized” terms. Specific values associated with an acceptable level of loss are expected to change over time as fabrication precision will improve and as fault-tolerant schemes may become more tolerant of higher losses, all of which are within the scope of the present disclosure.
For the purposes of the present disclosure, the phrase “A and/or B” means (A), (B), or (A and B), and the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). The term “between,” when used with reference to measurement ranges, is inclusive of the ends of the measurement ranges. As used herein, the notation “A/B/C” means (A), (B), and/or (C). The terms “substantially,” “close,” “approximately,” “near,” and “about,” generally refer to being within +/−20% of a target value based on the context of a particular value as described herein or as known in the art. Similarly, terms indicating orientation of various elements, e.g., “coplanar,” “perpendicular,” “orthogonal,” “parallel,” or any other angle between the elements, generally refer to being within +/−5-20% of a target value based on the context of a particular value as described herein or as known in the art.
The description uses the phrases “in an embodiment” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. The disclosure may use perspective-based descriptions such as “above,” “below,” “top,” “bottom,” and “side”; such descriptions are used to facilitate the discussion and are not intended to restrict the application of disclosed embodiments. The accompanying drawings are not necessarily drawn to scale. Unless otherwise specified, the use of the ordinal adjectives “first,” “second,” and “third,” etc., to describe a common object, merely indicate that different instances of like objects are being referred to and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner.
The terms “over,” “under,” “between,” and “on” as used herein refer to a relative position of one material layer or component with respect to other layers or components. For example, one layer disposed over or under another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer disposed between two layers may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in direct contact with that second layer. Similarly, unless explicitly stated otherwise, one feature disposed between two features may be in direct contact with the adjacent features or may have one or more intervening layers.
Various operations may be described as multiple discrete actions or operations in turn in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations may not be performed in the order of presentation. Operations described may be performed in a different order from the described embodiment. Various additional operations may be performed, and/or described operations may be omitted in additional embodiments.
Quantum Dot Formation Regions of Quantum Dot Devices
As described above, quantum dot devices are particularly promising for large-scale qubit implementation, such devices including a plurality of rows of a quantum dot formation region. In various embodiments, rows of quantum dot formation regions may be formed in different manners. In a first embodiment (where a quantum dot device may be referred to as a trench-based device), a row of a quantum dot formation region may be defined by an insulating material provided over a continuous quantum well stack, the insulating material including a trench corresponding to the row (i.e., multiple trenches if there are multiple rows of quantum dot formation regions), the trench extending toward the continuous quantum well stack, and portions of gate metals of different gates being at least partially in the trench. In such an embodiment, even though the quantum well stack is continuous along a portion of a plane, i.e., continuous in a two-dimensional plane, confinement of the quantum dot formation region to a row (i.e., confinement of the quantum dots formed in a region that is a row), i.e., confinement to substantially one direction, is achieved by the confinement to substantially one direction of the trench in the insulating material, the trench at least partially filled with one or more gate metals. Such embodiments of quantum dot devices are described below with reference to FIGS. 1-4. In a second embodiment (where a quantum dot device may be referred to as a fin-based device), a row of a quantum dot formation region may be defined by at least a portion of a quantum well stack being formed as a fin corresponding to the row (i.e., multiple fins if there are multiple rows of quantum dot formation regions), and portions of gate metals of different gates being over the fin. In such an embodiment, confinement of the quantum dot formation region to a row is achieved by the confining the quantum well stack to the fin. Thus, in contrast to the second embodiment, at least portions of the quantum well stack may not be horizontally continuous across different fins. Such embodiments are described below with reference to FIGS. 10-12. In various embodiments, the quantum dot devices disclosed herein may provide two-dimensional arrays of quantum dots (e.g., quantum dots 142) during operation, with the quantum dots constrained in “rows” by the quantum dot formation regions (e.g., quantum dot formation regions 111) and “columns” by the gates (e.g., gates 106/108), as discussed below. In some embodiments, individual ones of the gates (e.g., of the gates 106/108) may be shared between multiple quantum dot formation regions. Quantum circuit assemblies with synchronized operation of control circuits as described herein may be implemented with qubit devices implemented as trench-based quantum dot devices or as fin-based quantum dot devices (i.e., implemented as quantum dot devices with rows of quantum dot formation regions defined by either trenches or fins).
Example Trench-Based Quantum Dot Devices
One type of quantum dot devices includes devices having a base, a continuous quantum well layer extending over the base, an insulating material over the quantum well layer, one or more trenches in the insulating material, and one or more gates with gate metals at least partially disposed in the trenches. In such devices, the quantum well layer is not etched into fins, as in fin-based devices. A quantum dot formed in such a device may be constrained in the x-direction by the one or more gates, in the y-direction by the trench, and in the z-direction by the quantum well layer, as discussed in detail herein. Unlike previous approaches to quantum dot formation and manipulation, quantum dot devices with trenches provide strong spatial localization of the quantum dots (and therefore good control over quantum dot interactions and manipulation), good scalability in the number of quantum dots included in the device, and/or design flexibility in making electrical connections to the quantum dot devices to integrate the quantum dot devices in larger computing devices. Therefore, this type of a quantum dot device is described as a first example of a qubit device that may be controlled using a control circuit assembly configured to synchronize operation of various control circuits as described herein.
FIGS. 1-4 are cross-sectional and top-down views of a quantum dot device 100, in accordance with various embodiments. In particular, FIGS. 1-3 provide cross-sectional views of the quantum dot device 100, where FIG. 2 illustrates the quantum dot device 100 taken along the section A-A of FIG. 1 (while FIG. 1 illustrates the quantum dot device 100 taken along the section C-C of FIG. 2) and FIG. 3 illustrates the quantum dot device 100 taken along the section D-D of FIG. 2 (while FIG. 2 illustrates the quantum dot device 100 taken along the section A-A of FIG. 3), while FIG. 4 illustrates a top-down view of the quantum dot device 100 (i.e., a view taken along the section B-B of FIG. 1 with a number of components not shown to more readily illustrate how the gates 106/108 and the magnet line 121 may be patterned). FIG. 1 illustrates the quantum dot device 100 taken along the section E-E of FIG. 4. Although FIG. 1 indicates that the cross-section illustrated in FIG. 2 is taken through the trench 103-1, an analogous cross-section taken through the trench 103-2 may be identical, and thus the discussion of FIG. 2 refers generally to the “trench 103.”
The quantum dot device 100 may include a quantum well stack 146 disposed on a base 102. An insulating material 128 may be disposed above the quantum well stack 146, and multiple trenches 103 in the insulating material 128 may extend toward the quantum well stack 146. In the embodiment illustrated in FIGS. 1-4, a gate dielectric 114 may be disposed between the quantum well stack 146 and the insulating material 128 so as to provide the “bottom” of the trenches 103. A number of examples of quantum well stacks 146 are discussed below with reference to FIGS. 5-7.
Although only two trenches, 103-1 and 103-2, are shown in FIGS. 1-4, this is simply for ease of illustration, and more than two trenches 103 may be included in the quantum dot device 100. In some embodiments, the total number of trenches 103 included in the quantum dot device 100 is an even number, with the trenches 103 organized into pairs including one active trench 103 and one read trench 103, as discussed in detail below. When the quantum dot device 100 includes more than two trenches 103, the trenches 103 may be arranged in pairs in a line (e.g., 2N trenches total may be arranged in a 1×2N line, or a 2×N line) or in pairs in a larger array (e.g., 2N trenches total may be arranged as a 4×N/2 array, a 6×N/3 array, etc.). As illustrated in FIGS. 1, 3, and 4, in some embodiments, multiple trenches 103 may be oriented substantially in parallel. The discussion herein will largely focus on a single pair of trenches 103 for ease of illustration, but all the teachings of the present disclosure apply to quantum dot devices 100 with more trenches 103. Further, the use of the term “trench” should not be interpreted to require that the insulating material 128 is deposited first and then a portion of that insulating material 128 is excavated to form the trench 103 prior to depositing material in the trench 103; in various embodiments, the insulating material 128 may be deposited before or after deposition of the material that will ultimately be disposed in the trench 103.
The quantum dot device 100 of FIGS. 1-4 may include multiple quantum dot formation regions 111 (labeled in FIG. 4), defined by the parallel trenches 103 in the insulating material 128 disposed on top of the quantum well stack 146. These quantum dot formation regions 111 may be portions of the quantum well stack 146 in which quantum dots 142 may form during operation. The quantum dot formation regions 111 may be arranged as multiple parallel rows defined by the trenches 103, and the gates 106/108 may each extend over multiple ones of the quantum dot formation regions 111.
The quantum well stack 146 may include a quantum well layer (not shown in FIGS. 1-4 but discussed below with reference to the quantum well layer 152 of FIGS. 5-7). The quantum well layer included in the quantum well stack 146 may be arranged normal to the z-direction, and may provide a layer in which a two-dimensional electron gas (2DEG) may form to enable the generation of one or more quantum dots during operation of the quantum dot device 100, as discussed in further detail below. The quantum well layer itself may provide a geometric constraint on the z-location of quantum dots in the quantum well stack 146. To control the x- and y-location of quantum dots in the quantum well stack 146, voltages may be applied to gates disposed at least partially in the trenches 103 above the quantum well stack 146 to adjust the energy profile along the trenches 103 in the x- and y-direction and thereby constrain the x- and y-location of quantum dots within quantum wells (discussed in detail below with reference to the gates 106/108). The dimensions of the trenches 103 may take any suitable values. For example, in some embodiments, the trenches 103 may each have a width 162 between about 5 nanometers and 50 nanometers. In some embodiments, the trenches 103 may each have a depth 164 between about 40 nanometers and 400 nanometers (e.g., between about 50 nanometers and 350 nanometers, or equal to about 100 nanometers). The insulating material 128 may be a dielectric material (e.g., an interlayer dielectric), such as silicon oxide. In some embodiments, the insulating material 128 may be a chemical vapor deposition (CVD) or flowable CVD oxide. In some embodiments, the trenches 103 may be spaced apart by a distance 160 between about 30 nanometers and 300 nanometers.
Multiple gates may be disposed at least partially in each of the trenches 103. In the embodiment illustrated in FIG. 2, three gates 106 and two gates 108 are shown as distributed at least partially in a single trench 103. This particular number of gates is simply illustrative, and any suitable number of gates may be used. Additionally, in some embodiments, multiple groups of gates (like the gates illustrated in FIG. 2) may be disposed at least partially in the trench 103.
As shown in FIG. 2, the gate 108-1 may be disposed between the gates 106-1 and 106-2, and the gate 108-2 may be disposed between the gates 106-2 and 106-3. Each of the gates 106/108 may include a gate dielectric 114; in the embodiment illustrated in FIG. 2, the gate dielectric 114 for all of the gates 106/108 is provided by a common layer of gate dielectric material disposed between the quantum well stack 146 and the insulating material 128. In other embodiments, the gate dielectric 114 for each of the gates 106/108 may be provided by separate portions of gate dielectric 114 (i.e., the gate dielectric 114 may not be continuous across multiple ones of the gates 106/108). In some embodiments, the gate dielectric 114 may be a multilayer gate dielectric (e.g., with multiple materials used to improve the interface between the trench 103 and the corresponding gate metal). The gate dielectric 114 may be, for example, silicon oxide, aluminum oxide, or a high-k dielectric, such as hafnium oxide. More generally, the gate dielectric 114 may include elements such as hafnium, silicon, oxygen, titanium, tantalum, lanthanum, aluminum, zirconium, barium, strontium, yttrium, lead, scandium, niobium, and zinc. Examples of materials that may be used in the gate dielectric 114 may include, but are not limited to, hafnium oxide, hafnium silicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, tantalum oxide, tantalum silicon oxide, lead scandium tantalum oxide, and lead zinc niobate. In some embodiments, an annealing process may be carried out on the gate dielectric 114 to improve the quality of the gate dielectric 114.
Each of the gates 106 may include a gate metal 110 (including multiple layers of gate metal) and a hardmask 116. In particular, a first gate metal layer 110A may be disposed in the trench 103, and a second gate metal layer 110B may be disposed above the gate metal 110-1 and above the insulating material 128, as shown. The hardmask 116 may be formed of silicon nitride, silicon carbide, or another suitable material. The gate metal 110 may be disposed between the hardmask 116 and the gate dielectric 114, and the gate dielectric 114 may be disposed between the gate metal 110 and the quantum well stack 146. As shown in FIG. 1, in some embodiments, the gate metal 110 of a gate 106 may extend over the insulating material 128 and into a trench 103 in the insulating material 128. Only one portion of the hardmask 116 is labeled in FIG. 2 for ease of illustration.
In some embodiments, the gate metal 110 may be a superconductor, such as aluminum, titanium nitride, or niobium titanium nitride; any of these materials may be included in the first gate metal layer 110A and/or the second gate metal layer 110B. In some embodiments, the first gate metal layer 110A may have a different material composition than the second gate metal layer 110B. For example, the first gate metal layer 110A may be titanium nitride, while the second gate metal layer 110B may be a material different from titanium nitride, or vice versa. In some embodiments, the first gate metal layer 110A and the second gate metal layer 110B may have the same material composition but a different microstructure. These different microstructures may arise, for example, by different deposition and/or patterning techniques used to form the first gate metal layer 110A and the second gate metal layer 110B. For example, in some embodiments, the first gate metal layer 110A may have a microstructure including columnar grains (e.g., when the first gate metal layer 110A is initially blanket-deposited and then etched as part of a subtractive patterning process), while the second gate metal layer 110B may not exhibit a columnar grain structure. In some embodiments, a seam delineating the interface between the top surface of the first gate metal layer 110A and the bottom surface of the second gate metal layer 110B may be present in the quantum dot device 100.
In some embodiments, the hardmask 116 may not be present in the quantum dot device 100 (e.g., a hardmask like the hardmask 116 may be removed during processing). The sides of the gate metal 110 may be substantially parallel, as shown in FIG. 2, and insulating spacers 134 may be disposed on the sides of the gate metal 110 and the hardmask 116 along the longitudinal axis of the trench 103. As illustrated in FIG. 2, the spacers 134 may be thicker closer to the quantum well stack 146 and thinner farther away from the quantum well stack 146. In some embodiments, the spacers 134 may have a convex shape. The spacers 134 may be formed of any suitable material, such as a carbon-doped oxide, silicon nitride, silicon oxide, or other carbides or nitrides (e.g., silicon carbide, silicon nitride doped with carbon, and silicon oxynitride). As illustrated in FIG. 1, no spacer material may be disposed between the gate metal 110 and the sidewalls of the trench 103 in the y-direction.
Each of the gates 108 may include a gate metal 112 and a hardmask 118. The hardmask 118 may be formed of silicon nitride, silicon carbide, or another suitable material. The gate metal 112 may be disposed between the hardmask 118 and the gate dielectric 114, and the gate dielectric 114 may be disposed between the gate metal 112 and the quantum well stack 146. As shown in FIG. 3, in some embodiments, the gate metal 112 of a gate 108 may extend over the insulating material 128 and into a trench 103 in the insulating material 128. In the embodiment illustrated in FIG. 2, the hardmask 118 may extend over the hardmask 116 (and over the gate metal 110 of the gates 106), while in other embodiments, the hardmask 118 may not extend over the gate metal 110. In the embodiment of FIGS. 1-3, the gate metal 112 of the gates 108 may be provided by a single continuous layer of material (and may not, for example, include multiple different layers of gate metal, as was discussed above with reference to the gate metal 110 of the gates 106). In other embodiments, however, the gate metal 112 of the gates 108 may include multiple layers of gate metal, e.g., multiple layers similar to the first gate metal layer 110A and the second gate metal layer 110B. In some embodiments, the gate metal 112 may be a different metal from the first gate metal layer 110A and/or the second gate metal layer 110B; in other embodiments, the gate metal 112 and the first gate metal layer 110A and/or the second gate metal layer 110B may have the same material composition. In some embodiments, the gate metal 112 may be a superconductor, such as aluminum, titanium nitride, or niobium titanium nitride. In some embodiments, the hardmask 118 may not be present in the quantum dot device 100 (e.g., a hardmask like the hardmask 118 may be removed during processing).
The gate 108-1 may extend between the proximate spacers 134 on the sides of the gate 106-1 and the gate 106-2 along the longitudinal axis of the trench 103, as shown in FIG. 2. In some embodiments, the gate metal 112 of the gate 108-1 may extend between the spacers 134 on the sides of the gate 106-1 and the gate 106-2 along the longitudinal axis of the trench 103. Thus, the gate metal 112 of the gate 108-1 may have a shape that is substantially complementary to the shape of the spacers 134, as shown in FIG. 2. Similarly, the gate 108-2 may extend between the proximate spacers 134 on the sides of the gate 106-2 and the gate 106-3 along the longitudinal axis of the trench 103. In some embodiments in which the gate dielectric 114 is not a layer shared commonly between the gates 108 and 106, but instead is separately deposited in the trench 103 between the spacers 134, the gate dielectric 114 may extend at least partially up the sides of the spacers 134 (and up the proximate sidewalls of the trench 103), and the gate metal 112 may extend between the portions of gate dielectric 114 on the spacers 134 (and the proximate sidewalls of the trench 103). As illustrated in FIG. 3, in some embodiments, no spacer material may be disposed between the gate metal 112 and the sidewalls of the trench 103 in the y-direction; in other embodiments (not shown in the present drawings), spacers 134 may also be disposed between the gate metal 112 and the sidewalls of the trench 103 in the y-direction.
The dimensions of the gates 106/108 may take any suitable values. For example, in some embodiments, the z-height 166 of the gate metal 110 in the trench 103 may be between about 100 nanometers and 400 nanometers (e.g., approximately about 200 nanometers); the z-height 175 of the gate metal 112 may be in about the same range. This z-height 166 of the gate metal 110 in the trench 103 may represent the sum of the z-height of the first gate metal layer 110A (e.g., between about 40 nanometers and 300 nanometers) and the thickness of the second gate metal layer 110B (e.g., between about 25 nanometers and 100 nanometers, or approximately 50 nanometers). In embodiments like the ones illustrated in FIGS. 1-3, the z-height 175 of the gate metal 112 may be greater than the z-height 166 of the gate metal 110 (as can be seen in, e.g., FIG. 2). In some embodiments, the length 168 of the gate metal 110 (i.e., in the x-direction) may be between about 20 nanometers and 50 nanometers (e.g., about 30 nanometers). Although all of the gates 106 are illustrated in the accompanying drawings as having the same length 168 of the gate metal 110, in some embodiments, the “outermost” gates 106 (e.g., the gates 106-1 and 106-3 of the embodiment illustrated in FIG. 2) may have a greater length 168 than the “inner” gates 106 (e.g., the gate 106-2 in the embodiment illustrated in FIG. 2). Such longer “outside” gates 106 may provide spatial separation between the doped regions 140 and the areas under the gates 108 and the inner gates 106 in which quantum dots 142 may form, and thus may reduce the perturbations to the potential energy landscape under the gates 108 and the inner gates 106 caused by the doped regions 140.
In some embodiments, the distance 170 between adjacent ones of the gates 106 (e.g., as measured from the gate metal 110 of one gate 106 to the gate metal 110 of an adjacent gate 106 in the x-direction, as illustrated in FIG. 2) may be between about 40 nanometers and 100 nanometers (e.g., about 50 nanometers). In some embodiments, the thickness 172 of the spacers 134 may be between about 1 nanometer and 10 nanometers (e.g., between about 3 nanometers and 5 nanometers, between about 4 nanometers and 6 nanometers, or between about 4 nanometers and 7 nanometers). The length of the gate metal 112 (i.e., in the x-direction) may depend on the dimensions of the gates 106 and the spacers 134, as illustrated in FIG. 2. As indicated in FIGS. 1 and 3, the gates 106/108 in one trench 103 may extend over the insulating material 128 between that trench 103 and an adjacent trench 103, but may be isolated from their counterpart gates by the intervening insulating material 130 and spacers 134.
As shown in FIG. 2, the gates 106 and 108 may be alternatingly arranged in the x-direction. During operation of the quantum dot device 100, voltages may be applied to the gates 106/108 to adjust the potential energy in the quantum well stack 146 to create quantum wells of varying depths in which quantum dots 142 may form. Only one quantum dot 142 is labeled with a reference numeral in FIGS. 2 and 4 for ease of illustration, but five are indicated as dotted circles below each trench 103. The location of the quantum dots 142 in FIGS. 2 and 4 is not intended to indicate a particular geometric positioning of the quantum dots 142. The spacers 134 (and the insulating material 128) may themselves provide “passive” barriers between quantum dots under the gates 106/108 in the quantum well stack 146, and the voltages applied to different ones of the gates 106/108 may adjust the potential energy under the gates 106/108 in the quantum well stack 146; decreasing the potential energy under a gate 106/108 may enable the formation of a quantum dot under that gate 106/108, while increasing the potential energy under a gate 106/108 may form a quantum barrier under that gate 106/108.
The quantum well stack 146 may include doped regions 140 that may serve as a reservoir of charge carriers for the quantum dot device 100. For example, an n-type doped region 140 may supply electrons for electron-type quantum dots 142, and a p-type doped region 140 may supply holes for hole-type quantum dots 142. In some embodiments, an interface material 141 may be disposed at a surface of a doped region 140, as shown. The interface material 141 may facilitate electrical coupling between a conductive contact (e.g., a conductive via 136, as discussed below) and the doped region 140. The interface material 141 may be any suitable metal-semiconductor ohmic contact material; for example, in embodiments in which the doped region 140 includes silicon, the interface material 141 may include nickel silicide, aluminum silicide, titanium silicide, molybdenum silicide, cobalt silicide, tungsten silicide, or platinum silicide. In some embodiments, the interface material 141 may be a non-silicide compound, such as titanium nitride. In some embodiments, the interface material 141 may be a metal (e.g., aluminum, tungsten, or indium).
The quantum dot devices 100 disclosed herein may be used to form electron-type or hole-type quantum dots 142. Note that the polarity of the voltages applied to the gates 106/108 to form quantum wells/barriers depends on the charge carriers used in the quantum dot device 100. In embodiments in which the charge carriers are electrons (and thus the quantum dots 142 are electron-type quantum dots), amply negative voltages applied to a gate 106/108 may increase the potential barrier under the gate 106/108, and amply positive voltages applied to a gate 106/108 may decrease the potential barrier under the gate 106/108 (thereby forming a potential well in which an electron-type quantum dot 142 may form). In embodiments in which the charge carriers are holes (and thus the quantum dots 142 are hole-type quantum dots), amply positive voltages applied to a gate 106/108 may increase the potential barrier under the gate 106/108, and amply negative voltages applied to a gate 106 and 108 may decrease the potential barrier under the gate 106/108 (thereby forming a potential well in which a hole-type quantum dot 142 may form). The quantum dot devices 100 disclosed herein may be used to form electron-type or hole-type quantum dots.
Voltages may be applied to each of the gates 106 and 108 separately to adjust the potential energy in the quantum well stack 146 under the gates 106 and 108, and thereby control the formation of quantum dots 142 under each of the gates 106 and 108. Additionally, the relative potential energy profiles under different ones of the gates 106 and 108 allow the quantum dot device 100 to tune the potential interaction between quantum dots 142 under adjacent gates. For example, if two adjacent quantum dots 142 (e.g., one quantum dot 142 under a gate 106 and another quantum dot 142 under an adjacent gate 108) are separated by only a short potential barrier, the two quantum dots 142 may interact more strongly than if they were separated by a taller potential barrier. Since the depth of the potential wells/height of the potential barriers under each gate 106/108 may be adjusted by adjusting the voltages on the respective gates 106/108, the differences in potential between adjacent gates 106/108 may be adjusted, and thus the interaction tuned.
In some applications, the gates 108 may be used as plunger gates to enable the formation of quantum dots 142 under the gates 108, while the gates 106 may be used as barrier gates to adjust the potential barrier between quantum dots 142 formed under adjacent gates 108. In other applications, the gates 108 may be used as barrier gates, while the gates 106 are used as plunger gates. In other applications, quantum dots 142 may be formed under all of the gates 106 and 108, or under any desired subset of the gates 106 and 108.
Conductive vias and lines may make contact with the gates 106/108, and to the doped regions 140, to enable electrical connection to the gates 106/108 and the doped regions 140 to be made in desired locations. As shown in FIGS. 1-4, the gates 106 may extend both “vertically” and “horizontally” away from the quantum well stack 146, and conductive vias 120 may contact the gates 106 (and are drawn in dashed lines in FIG. 2 to indicate their location behind the plane of the drawing). The conductive vias 120 may extend through the hardmask 116 and the hardmask 118 to contact the gate metal 110 of the gates 106. The gates 108 may similarly extend away from the quantum well stack 146, and conductive vias 122 may contact the gates 108 (also drawn in dashed lines in FIG. 2 to indicate their location behind the plane of the drawing). The conductive vias 122 may extend through the hardmask 118 to contact the gate metal 112 of the gates 108. Conductive vias 136 may contact the interface material 141 and may thereby make electrical contact with the doped regions 140. The quantum dot device 100 may include further conductive vias and/or lines (not shown) to make electrical contact to the gates 106/108 and/or the doped regions 140, as desired. The conductive vias and lines included in a quantum dot device 100 may include any suitable materials, such as copper, tungsten (deposited, e.g., by CVD), or a superconductor (e.g., aluminum, tin, titanium nitride, niobium titanium nitride, tantalum, niobium, or other niobium compounds such as niobium tin and niobium germanium).
During operation, a bias voltage may be applied to the doped regions 140 (e.g., via the conductive vias 136 and the interface material 141) to cause current to flow through the doped regions 140 and through a quantum well layer of the quantum well stack 146 (discussed in further detail below with reference to FIGS. 5-7). When the doped regions 140 are doped with an n-type material, this voltage may be positive; when the doped regions 140 are doped with a p-type material, this voltage may be negative. The magnitude of this bias voltage may take any suitable value (e.g., between about 0.25 volts and 2 volts).
In some embodiments, the quantum dot device 100 may include one or more magnet lines 121. For example, a single magnet line 121 is illustrated in FIGS. 1-4, proximate to the trench 103-1. The magnet line 121 may be formed of a conductive material and may be used to conduct current pulses that generate magnetic fields to influence the spin states of one or more of the quantum dots 142 that may form in the quantum well stack 146. In some embodiments, the magnet line 121 may conduct a pulse to reset (or “scramble”) nuclear and/or quantum dot spins. In some embodiments, the magnet line 121 may conduct a pulse to initialize an electron in a quantum dot in a particular spin state. In some embodiments, the magnet line 121 may conduct current to provide a continuous, oscillating magnetic field to which the spin of a qubit may couple. The magnet line 121 may provide any suitable combination of these embodiments, or any other appropriate functionality.
In some embodiments, the magnet line 121 may be formed of copper. In some embodiments, the magnet line 121 may be formed of a superconductor, such as aluminum. The magnet line 121 illustrated in FIGS. 1-4 is non-coplanar with the trenches 103, and is also non-coplanar with the gates 106/108. In some embodiments, the magnet line 121 may be spaced apart from the gates 106/108, in the direction of the z-axis of the example coordinate system shown, by a distance 167. The distance 167 may take any suitable value (e.g., based on the desired strength of magnetic field interaction with particular quantum dots 142); in some embodiments, the distance 167 may be between about 25 nanometers and 1 micron (e.g., between about 50 nanometers and 200 nanometers).
In some embodiments, the magnet line 121 may be formed of a magnetic material. For example, a magnetic material (such as cobalt) may be deposited in a trench in the insulating material 130 to provide a permanent magnetic field in the quantum dot device 100.
The magnet line 121 may have any suitable dimensions. For example, the magnet line 121 may have a thickness 169 between about 25 nanometers and 100 nanometers. The magnet line 121 may have a width 171 between about 25 nanometers and 100 nanometers. In some embodiments, the width 171 and thickness 169 of a magnet line 121 may be substantially equal to, respectively, the width and thickness of other conductive lines in the quantum dot device 100 (not shown) used to provide electrical interconnects, as known in the art. The magnet line 121 may have a length 173 that may depend on the number and dimensions of the gates 106/108 that are to form quantum dots 142 with which the magnet line 121 is to interact. The magnet line 121 illustrated in FIGS. 1-4 is substantially linear, but this need not be the case; in general, the magnet lines 121 of the quantum dot devices 100 may take any suitable shape. In other embodiments, micro-magnets may be used instead or in addition to the magnet line 121. Conductive vias 123 may contact the magnet line 121.
The conductive vias 120, 122, 136, and 123 may be electrically isolated from each other by an insulating material 130. The insulating material 130 may be any suitable material, such as an interlayer dielectric (ILD). Examples of the insulating material 130 may include silicon oxide, silicon nitride, aluminum oxide, carbon-doped oxide, and/or silicon oxynitride. As known in the art of IC manufacturing, conductive vias and lines may be formed in an iterative process in which layers of structures are formed on top of each other. In some embodiments, the conductive vias 120/122/136/123 may have a width that is about 20 nanometers or greater at their widest point (e.g., about 30 nanometers), and a pitch of about 80 nanometers or greater (e.g., about 100 nanometers). In some embodiments, conductive lines (not shown) included in the quantum dot device 100 may have a width that is about 100 nanometers or greater, and a pitch of about 100 nanometers or greater. The particular arrangement of conductive vias shown in FIGS. 1-4 is simply illustrative, and any electrical routing arrangement may be implemented.
As discussed above, the structure of the trench 103-1 may be the same as the structure of the trench 103-2; similarly, the construction of gates 106/108 in and around the trench 103-1 may be the same as the construction of gates 106/108 in and around the trench 103-2. The gates 106/108 associated with the trench 103-1 may be mirrored by corresponding gates 106/108 associated with the parallel trench 103-2, and the insulating material 130 may separate the gates 106/108 associated with the different trenches 103-1 and 103-2. In particular, quantum dots 142 formed in the quantum well stack 146 under the trench 103-1 (under the gates 106/108) may have counterpart quantum dots 142 in the quantum well stack 146 under the trench 103-2 (under the corresponding gates 106/108). In some embodiments, the quantum dots 142 under the trench 103-1 may be used as “active” quantum dots in the sense that these quantum dots 142 act as qubits and are controlled (e.g., by voltages applied to the gates 106/108 associated with the trench 103-1) to perform quantum computations. The quantum dots 142 associated with the trench 103-2 may be used as “read” quantum dots in the sense that these quantum dots 142 may sense the quantum state of the quantum dots 142 under the trench 103-1 by detecting the electric field generated by the charge in the quantum dots 142 under the trench 103-1, and may convert the quantum state of the quantum dots 142 under the trench 103-1 into electrical signals that may be detected by the gates 106/108 associated with the trench 103-2. Each quantum dot 142 under the trench 103-1 may be read by its corresponding quantum dot 142 under the trench 103-2. Thus, the quantum dot device 100 enables both quantum computation and the ability to read the results of a quantum computation.
As discussed above, the quantum well stack 146 may include a quantum well layer in which a 2DEG may form during operation of the quantum dot device 100. The quantum well stack 146 may take any of a number of forms, several of which are illustrated in FIGS. 5-7. The various layers in the quantum well stacks 146 discussed below may be grown on the base 102 (e.g., using epitaxial processes).
Although the singular term “layer” may be used to refer to various components of the quantum well stacks 146 of FIGS. 5-7, any of the layers discussed below may include multiple materials arranged in any suitable manner. In embodiments in which a quantum well stack 146 includes layers other than a quantum well layer 152, layers other than the quantum well layer 152 in a quantum well stack 146 may have higher threshold voltages for conduction than the quantum well layer 152 so that when the quantum well layer 152 is biased at its threshold voltages, the quantum well layer 152 conducts and the other layers of the quantum well stack 146 do not. This may avoid parallel conduction in both the quantum well layer 152 and the other layers, and thus avoid compromising the strong mobility of the quantum well layer 152 with conduction in layers having inferior mobility. In some embodiments, silicon used in a quantum well stack 146 (e.g., in a quantum well layer 152) may be grown from precursors enriched with the 28Si isotope. In some embodiments, germanium used in a quantum well stack 146 (e.g., in a quantum well layer 152) may be grown from precursors enriched with the 70Ge, 72Ge, or 74Ge isotope.
FIG. 5 is a cross-sectional view of a quantum well stack 146 including only a quantum well layer 152. The quantum well layer 152 may be disposed on the base 102, and may be formed of a material such that, during operation of the quantum dot device 100, a 2DEG may form in the quantum well layer 152 proximate to the upper surface of the quantum well layer 152. The gate dielectric 114 of the gates 106/108 may be disposed on the upper surface of the quantum well layer 152. In some embodiments, the quantum well layer 152 of FIG. 5 may be formed of intrinsic silicon, and the gate dielectric 114 may be formed of silicon oxide; in such an arrangement, during use of the quantum dot device 100, a 2DEG may form in the intrinsic silicon at the interface between the intrinsic silicon and the silicon oxide. Embodiments in which the quantum well layer 152 of FIG. 5 is formed of intrinsic silicon may be particularly advantageous for electron-type quantum dot devices 100. In some embodiments, the quantum well layer 152 of FIG. 5 may be formed of intrinsic germanium, and the gate dielectric 114 may be formed of germanium oxide; in such an arrangement, during use of the quantum dot device 100, a two-dimensional hole gas (2DHG) may form in the intrinsic germanium at the interface between the intrinsic germanium and the germanium oxide. Such embodiments may be particularly advantageous for hole-type quantum dot devices 100. In some embodiments, the quantum well layer 152 may be strained, while in other embodiments, the quantum well layer 152 may not be strained. The thicknesses (i.e., z-heights) of the layers in the quantum well stack 146 of FIG. 5 may take any suitable values. For example, in some embodiments, the thickness of the quantum well layer 152 (e.g., intrinsic silicon or germanium) may be between about 0.8 microns and 1.2 microns.
FIG. 6 is a cross-sectional view of a quantum well stack 146 including a quantum well layer 152 and a barrier layer 154. The quantum well stack 146 may be disposed on the base 102 (e.g., as discussed above with reference to FIG. 6) such that the barrier layer 154 is disposed between the quantum well layer 152 and the base 102. The barrier layer 154 may provide a potential barrier between the quantum well layer 152 and the base 102. As discussed above with reference to FIG. 5, the quantum well layer 152 of FIG. 6 may be formed of a material such that, during operation of the quantum dot device 100, a 2DEG may form in the quantum well layer 152 proximate to the upper surface of the quantum well layer 152. For example, in some embodiments in which the base 102 is formed of silicon, the quantum well layer 152 of FIG. 6 may be formed of silicon, and the barrier layer 154 may be formed of silicon germanium. The germanium content of this silicon germanium may be about 20-80% (e.g., about 30%). In some embodiments in which the quantum well layer 152 is formed of germanium, the barrier layer 154 may be formed of silicon germanium, e.g., with a germanium content of about 20-80% (e.g., about 70%). The thicknesses (i.e., z-heights) of the layers in the quantum well stack 146 of FIG. 6 may take any suitable values. For example, in some embodiments, the thickness of the barrier layer 154 (e.g., silicon germanium) may be between about 0 nanometers and 400 nanometers. In some embodiments, the thickness of the quantum well layer 152 (e.g., silicon or germanium) may be between about 5 nanometers and 30 nanometers.
FIG. 7 is a cross-sectional view of a quantum well stack 146 including a quantum well layer 152 and a barrier layer 154-1, as well as a buffer layer 176 and an additional barrier layer 154-2. The quantum well stack 146 may be disposed on the base 102 such that the buffer layer 176 is disposed between the barrier layer 154-1 and the base 102. The buffer layer 176 may be formed of the same material as the barrier layer 154, and may be present to trap defects that form in this material as it is grown on the base 102. In some embodiments, the buffer layer 176 may be grown under different conditions (e.g., deposition temperature or growth rate) from the barrier layer 154-1. In particular, the barrier layer 154-1 may be grown under conditions that achieve fewer defects than the buffer layer 176. In some embodiments in which the buffer layer 176 includes silicon germanium, the silicon germanium of the buffer layer 176 may have a germanium content that varies from the base 102 to the barrier layer 154-1; for example, the silicon germanium of the buffer layer 176 may have a germanium content that varies from zero percent at the silicon base 102 to a nonzero percent (e.g., about 30%) at the barrier layer 154-1. The thicknesses (i.e., z-heights) of the layers in the quantum well stack 146 of FIG. 7 may take any suitable values. For example, in some embodiments, the thickness of the buffer layer 176 (e.g., silicon germanium) may be between about 0.3 microns and 4 microns (e.g., between about 0.3 microns and 2 microns, or about 0.5 microns). In some embodiments, the thickness of the barrier layer 154-1 (e.g., silicon germanium) may be between about 0 nanometers and 400 nanometers. In some embodiments, the thickness of the quantum well layer 152 (e.g., silicon or germanium) may be between about 5 nanometers and 30 nanometers (e.g., about 10 nanometers). The barrier layer 154-2, like the barrier layer 154-1, may provide a potential energy barrier around the quantum well layer 152, and may take the form of any of the embodiments of the barrier layer 154-1. In some embodiments, the thickness of the barrier layer 154-2 (e.g., silicon germanium) may be between about 25 nanometers and 75 nanometers (e.g., about 32 nanometers).
As discussed above with reference to FIG. 6, the quantum well layer 152 of FIG. 7 may be formed of a material such that, during operation of the quantum dot device 100, a 2DEG may form in the quantum well layer 152 proximate to the upper surface of the quantum well layer 152. For example, in some embodiments in which the base 102 is formed of silicon, the quantum well layer 152 of FIG. 7 may be formed of silicon, and the barrier layer 154-1 and the buffer layer 176 may be formed of silicon germanium. In some such embodiments, the silicon germanium of the buffer layer 176 may have a germanium content that varies from the base 102 to the barrier layer 154-1; for example, the silicon germanium of the buffer layer 176 may have a germanium content that varies from zero percent at the silicon base 102 to a nonzero percent (e.g., about 30%) at the barrier layer 154-1. In other embodiments, the buffer layer 176 may have a germanium content about equal to the germanium content of the barrier layer 154-1 but may be thicker than the barrier layer 154-1 so as to absorb the defects that arise during growth.
In some embodiments, the quantum well layer 152 of FIG. 7 may be formed of germanium, and the buffer layer 176 and the barrier layer 154-1 may be formed of silicon germanium. In some such embodiments, the silicon germanium of the buffer layer 176 may have a germanium content that varies from the base 102 to the barrier layer 154-1; for example, the silicon germanium of the buffer layer 176 may have a germanium content that varies from zero percent at the base 102 to a nonzero percent (e.g., about 70%) at the barrier layer 154-1. The barrier layer 154-1 may in turn have a germanium content equal to the nonzero percent. In other embodiments, the buffer layer 176 may have a germanium content about equal to the germanium content of the barrier layer 154-1 but may be thicker than the barrier layer 154-1 so as to absorb the defects that arise during growth. In some embodiments of the quantum well stack 146 of FIG. 7, the buffer layer 176 and/or the barrier layer 154-2 may be omitted.
The outer spacers 134 on the outer gates 106, shown, e.g., in FIG. 2, may provide a doping boundary, limiting diffusion of the dopant from the doped regions 140 into the area under the gates 106/108. In some embodiments, the doped regions 140 may extend past the outer spacers 134 and under the outer gates 106. For example, as illustrated in FIG. 8, the doped region 140 may extend past the outer spacers 134 and under the outer gates 106 by a distance 182 between about 0 nanometers and 10 nanometers. In some embodiments, the doped regions 140 may not extend past the outer spacers 134 toward the outer gates 106, but may instead “terminate” under the outer spacers 134. For example, as illustrated in FIG. 9, the doped regions 140 may be spaced away from the interface between the outer spacers 134 and the outer gates 106 by a distance 184 between about 0 nanometers and 10 nanometers. The interface material 141 is omitted from FIGS. 8 and 9 for ease of illustration.
Example Fin-Based Quantum Dot Devices
Another type of quantum dot devices includes devices having a base, a fin extending away from the base, where the fin includes a quantum well layer, and one or more gates disposed on the fin. A quantum dot formed in such a device may be constrained in the x-direction by the one or more gates, in the y-direction by the fin, and in the z-direction by the quantum well layer, as discussed in detail herein. Similar to the quantum dot devices with trenches, described above, and unlike previous approaches to quantum dot formation and manipulation, quantum dot devices with fins provide strong spatial localization of the quantum dots (and therefore good control over quantum dot interactions and manipulation), good scalability in the number of quantum dots included in the device, and/or design flexibility in making electrical connections to the quantum dot devices to integrate the quantum dot devices in larger computing devices. Therefore, this type of a quantum dot device is described as another example of a qubit device that may be controlled using a control circuit assembly configured to synchronize operation of various control circuits as described herein.
FIGS. 10-12 are cross-sectional views of an example quantum dot device 200 implementing quantum dot qubits, in accordance with various embodiments. In particular, FIG. 11 illustrates the quantum dot device 200 taken along the section A-A of FIG. 10 (while FIG. 10 illustrates the quantum dot device 200 taken along the section C-C of FIG. 11), and FIG. 12 illustrates the quantum dot device 200 taken along the section B-B of FIG. 10 (while FIG. 10 illustrates a quantum dot device 200 taken along the section D-D of FIG. 12). Although FIG. 10 indicates that the cross-section illustrated in FIG. 11 is taken through the fin 104-1, an analogous cross-section taken through the fin 104-2 may be identical, and thus the discussion of FIGS. 10-12 refers generally to the “fin 104.”
As shown in FIGS. 10-12, the quantum dot device 200 may include a base 102, similar to the base 102 of the quantum dot device 200 shown in FIGS. 1-4, and multiple fins 104 extending away from the base 102. The base 102 and the fins 104 may include a semiconductor substrate and a quantum well stack (not shown in FIGS. 10-12 but discussed below with reference to the semiconductor substrate 144 and the quantum well stack 146), distributed in any of a number of ways between the base 102 and the fins 104. The base 102 may include at least some of the semiconductor substrate, and the fins 104 may each include a quantum well layer, e.g., a quantum well layer as discussed above with reference to the quantum well layer 152 of FIGS. 5-7. Examples of base/fin arrangements are discussed below with reference to the base fin arrangements 158 of FIGS. 13-19.
Although only two fins, 104-1 and 104-2, are shown in FIGS. 10-12, this is simply for ease of illustration, and more than two fins 104 may be included in the quantum dot device 200. In some embodiments, the total number of fins 104 included in the quantum dot device 200 is an even number, with the fins 104 organized into pairs including one active fin 104 and one read fin 104, as discussed in detail below. When the quantum dot device 200 includes more than two fins 104, the fins 104 may be arranged in pairs in a line (e.g., 2N fins total may be arranged in a 1×2N line, or a 2×N line) or in pairs in a larger array (e.g., 2N fins total may be arranged as a 4×N/2 array, a 6×N/3 array, etc.). As illustrated in FIGS. 10 and 12, in some embodiments, multiple fins 104 may be oriented substantially in parallel. The discussion herein will largely focus on a single pair of fins 104 for ease of illustration, but all the teachings of the present disclosure apply to quantum dot devices 200 with more fins 104.
The quantum dot device 200 of FIGS. 10-12 may include multiple quantum dot formation regions 111 (labeled in FIG. 12), defined by the fins 104. These quantum dot formation regions 111 may be portions of the quantum well stack 146 in which quantum dots 142 may form during operation. The quantum dot formation regions 111 may be arranged as multiple parallel rows defined by the insulating material 188, and the gates 106/108 may each extend over multiple ones of the quantum dot formation regions 111. In the embodiments discussed with reference to FIGS. 10-12, the quantum dot formation regions 111 may be defined by fins 104 separated by portions of insulating material 188; these fins 104 may provide parallel rows of portions of quantum well layers 152 in which quantum dots 142 may form. Thus, the quantum dot formation regions 111 of the quantum dot device 200 of FIGS. 10-12 and of the quantum dot device 100 of FIGS. 1-4 illustrate two different ways of defining the quantum dot formation regions 111.
As noted above, each of the fins 104 may include a quantum well layer (not shown in FIGS. 10-12 but discussed above with reference to the quantum well layer 152). The quantum well layer included in the fins 104 may be arranged normal to the z-direction, and may provide a layer in which a 2DEG may form to enable the generation of a quantum dot during operation of the quantum dot device 200, as discussed in further detail below. The quantum well layer itself may provide a geometric constraint on the z-location of quantum dots in the fins 104, and the limited extent of the fins 104 (and therefore the quantum well layer) in the y-direction may provide a geometric constraint on the y-location of quantum dots in the fins 104. To control the x-location of quantum dots in the fins 104, voltages may be applied to gates disposed on the fins 104 to adjust the energy profile along the fins 104 in the x-direction and thereby constrain the x-location of quantum dots within quantum wells (discussed in detail below with reference to the gates 106/108). The dimensions of the fins 104 may take any suitable values. For example, in some embodiments, the fins 104 may each have a width 180 between about 5 and 80 nanometers. In some embodiments, the fins 104 may each have a height 186 between about 100 and 400 nanometers (e.g., between about 150 and 350 nanometers, or equal to about 300 nanometers).
The fins 104 may be arranged in parallel, as illustrated in FIGS. 10 and 12, and may be spaced apart by an insulating material 188, which may be disposed on opposite faces of the fins 104. The insulating material 188 of the quantum dot device 200 may be a dielectric material, such as silicon oxide, similar to the insulating material 128 of the quantum dot device 100. For example, in some embodiments, the fins 104 may be spaced apart by a distance 190 between about 100 and 250 microns.
Multiple gates may be disposed on each of the fins 104. In the embodiment illustrated in FIG. 11, three gates 106 and two gates 108 are shown as distributed on the top of the fin 104. This particular number of gates is simply illustrative, and any suitable number of gates may be used. Additionally, multiple groups of gates like the gates illustrated in FIG. 11 may be disposed on the fin 104.
Similar to the quantum dot device 100, in the quantum dot device 200, as shown in FIG. 11, the gate 108-1 may be disposed between the gates 106-1 and 106-2, and the gate 108-2 may be disposed between the gates 106-2 and 106-3, and each of the gates 106/108 may include a gate dielectric 114. In the embodiment illustrated in FIG. 11, the gate dielectric 114 for all of the gates 106/108 is provided by a common layer of gate dielectric material. In other embodiments, the gate dielectric 114 for each of the gates 106/108 of the quantum dot device 200 may be provided by separate portions of gate dielectric 114. Descriptions provided with respect to materials of the gate dielectric 114 of the quantum dot device 100 are applicable to the gate dielectric 114 of the quantum dot device 200 and, therefore, are not repeated.
In the quantum dot device 200, each of the gates 106 may include a gate metal 110 and a hardmask 116, similar to those of the quantum dot device 100. The gate metal 110 may be disposed between the hardmask 116 and the gate dielectric 114, and the gate dielectric 114 may be disposed between the gate metal 110 and the fin 104. Only one portion of the hardmask 116 is labeled in FIG. 11 for ease of illustration. In some embodiments, the hardmask 116 may not be present in the quantum dot device 200 (e.g., a hardmask like the hardmask 116 may be removed during processing). In the quantum dot device 200, the sides of the gate metal 110 may be substantially parallel, as shown in FIG. 11, and insulating spacers 134 may be disposed on the sides of the gate metal 110 and the hardmask 116, similar to the insulating spacers 134 of the quantum dot device 100. As illustrated in FIG. 11, the spacers 134 may be thicker closer to the fin 104 and thinner farther away from the fin 104. In some embodiments, the spacers 134 may have a convex shape. Descriptions provided with respect to materials of the gate metal 110, the hardmask 116, and the spacers 134 of the quantum dot device 100 are applicable to those of the quantum dot device 200 and, therefore, are not repeated.
In the quantum dot device 200, each of the gates 108 may include a gate metal 112 and a hardmask 118, similar to those of the quantum dot device 100. The gate metal 112 may be disposed between the hardmask 118 and the gate dielectric 114, and the gate dielectric 114 may be disposed between the gate metal 112 and the fin 104. In the embodiment illustrated in FIG. 11, the hardmask 118 may extend over the hardmask 116 (and over the gate metal 110 of the gates 106), while in other embodiments, the hardmask 118 may not extend over the gate metal 110. In some embodiments, the gate metal 112 may be a different metal from the gate metal 110; in other embodiments, the gate metal 112 and the gate metal 110 may have the same material composition. In some embodiments, the hardmask 118 may not be present in the quantum dot device 200 (e.g., a hardmask like the hardmask 118 may be removed during processing). Descriptions provided with respect to materials of the gate metal 112 and the hardmask 118 of the quantum dot device 100 are applicable to those of the quantum dot device 200 and, therefore, are not repeated.
The gate 108-1 may extend between the proximate spacers 134 on the sides of the gate 106-1 and the gate 106-2 along the longitudinal axis of the fin 104, as shown in FIG. 11. In some embodiments, the gate metal 112 of the gate 108-1 may extend between the spacers 134 on the sides of the gate 106-1 and the gate 106-2 along the longitudinal axis of the fin 104. Thus, the gate metal 112 may have a shape that is substantially complementary to the shape of the spacers 134, as shown in FIG. 11. Similarly, the gate 108-2 may extend between the proximate spacers 134 on the sides of the gate 106-2 and the gate 106-3 along the longitudinal axis of the fin 104. In some embodiments in which the gate dielectric 114 is not a layer shared commonly between the gates 108 and 106, but instead is separately deposited on the fin 104 between the spacers 134, the gate dielectric 114 may extend at least partially up the sides of the spacers 134, and the gate metal 112 may extend between the portions of gate dielectric 114 on the spacers 134. The gate metal 112, like the gate metal 110, may be any suitable metal, such as titanium nitride.
The dimensions of the gates 106/108 in the quantum dot device 200 may take any suitable values. For example, in some embodiments, the z-height 192 of the gate metal 110 may be between about 40 and 75 nanometers (e.g., approximately about 50 nanometers); the z-height of the gate metal 112 may be in the same range. In embodiments like the ones illustrated in FIG. 11, the z-height of the gate metal 112 may be greater than the z-height of the gate metal 110. In some embodiments, the length 168 of the gate metal 110 (i.e., in the x-direction) in the quantum dot device 200 may be substantially the same as in the quantum dot device 100, e.g., between about 20 and 40 nanometers (e.g., about 30 nanometers). In some embodiments, the distance 170 and/or the thickness 172 shown for the quantum dot device 200 of FIG. 11 may be substantially the same as those shown for the quantum dot device 100 of FIG. 2. The length of the gate metal 112 (i.e., in the x-direction) may depend on the dimensions of the gates 106 and the spacers 134, as illustrated in FIG. 11. As indicated in FIG. 10, the gates 106/108 on one fin 104 may extend over the insulating material 188 beyond their respective fins 104 and towards the other fin 104, but may be isolated from their counterpart gates by the intervening insulating material 130.
In the embodiment of the quantum dot device 200 illustrated in FIG. 11, the z-height of the gate metal 112 of the gates 108 may be approximately equal to the sum of the z-height of the gate metal 110 and the z-height of the hardmask 116, as shown. Also, in the embodiment of FIG. 11, the gate metal 112 of the gates 108 may not extend in the x-direction beyond the adjacent spacers 134. In other embodiments, the z-height of the gate metal 112 of the gates 108 may be greater than the sum of the z-height of the gate metal 110 and the z-height of the hardmask 116, and in some such embodiments, the gate metal 112 of the gates may extend beyond the spacers 134 in the x-direction.
As shown in FIG. 11, the gates 106 and 108 may be alternatingly arranged along the fin 104 in the x-direction. During operation of the quantum dot device 200, voltages may be applied to the gates 106/108 to adjust the potential energy in the quantum well layer (not shown) in the fin 104 to create quantum wells of varying depths in which quantum dots 142 may form. Only one quantum dot 142 is labeled with a reference numeral in FIGS. 11 and 12 for ease of illustration, but five are indicated as dotted circles in each fin 104, forming what may be referred to as a “quantum dot array.” The location of the quantum dots 142 in FIG. 11 is not intended to indicate a particular geometric positioning of the quantum dots 142. Similar to the quantum dot device 100, in the quantum dot device 200, the spacers 134 may themselves provide “passive” barriers between quantum wells under the gates 106/108 in the quantum well layer, and the voltages applied to different ones of the gates 106/108 may adjust the potential energy under the gates 106/108 in the quantum well layer; decreasing the potential energy may form quantum wells, while increasing the potential energy may form quantum barriers.
The fins 104 may include doped regions 140 that may serve as a reservoir of charge carriers for the quantum dot device 200. Descriptions of the n-type doped region 140, the p-type doped region 140, the interface material 141, how the voltages may be applied to the gates 106/108 to form quantum wells/barriers, how the gates 108 may be used as plunger gates while the gates 106 may be used as barrier gates, and of conductive vias and lines that may make contact with the gates 106/108 and with the doped regions 140, provided with respect to the quantum dot device 100 are applicable to the quantum dot device 200 and, therefore, are not repeated. As shown in FIGS. 10-12, the gates 106 may extend away from the fins 104, and conductive vias 120 may contact the gates 106 (and are drawn in dashed lines in FIG. 11 to indicate their location behind the plane of the drawing). The gates 108 may similarly extend away from the fins 104, and conductive vias 122 may contact the gates 108 (also drawn in dashed lines in FIG. 11 to indicate their location behind the plane of the drawing). The quantum dot device 200 may include further conductive vias and/or lines (not shown) to make electrical contact to the gates 106/108 and/or the doped regions 140, as desired. Descriptions of the bias voltage that may be applied to the doped regions 140 and of the conductive vias 120, 122, and 136, provided with respect to the quantum dot device 100 are applicable to the quantum dot device 200 and, therefore, are not repeated. Furthermore, although not shown in FIGS. 10-12, in some embodiments, the quantum dot device 200 may include one or more magnet lines such as the magnet line 121 described with reference to the quantum dot device 100.
As discussed above, the structure of the fin 104-1 may be the same as the structure of the fin 104-2; similarly, the construction of gates 106/108 on the fin 104-1 may be the same as the construction of gates 106/108 on the fin 104-2. The gates 106/108 on the fin 104-1 may be mirrored by corresponding gates 106/108 on the parallel fin 104-2, and the insulating material 130 may separate the gates 106/108 on the different fins 104-1 and 104-2. In particular, quantum dots 142 formed in the fin 104-1 (under the gates 106/108) may have counterpart quantum dots 142 in the fin 104-2 (under the corresponding gates 106/108). In some embodiments, the quantum dots 142 in the fin 104-1 may be used as “active” quantum dots in the sense that these quantum dots 142 act as qubits and are controlled (e.g., by voltages applied to the gates 106/108 of the fin 104-1) to perform quantum computations. The quantum dots 142 in the fin 104-2 may be used as “read” quantum dots in the sense that these quantum dots 142 may sense the quantum state of the quantum dots 142 in the fin 104-1 by detecting the electric field generated by the charge in the quantum dots 142 in the fin 104-1, and may convert the quantum state of the quantum dots 142 in the fin 104-1 into electrical signals that may be detected by the gates 106/108 on the fin 104-2. Each quantum dot 142 in the fin 104-1 may be read by its corresponding quantum dot 142 in the fin 104-2. Thus, the quantum dot device 200 enables both quantum computation and the ability to read the results of a quantum computation.
As discussed above, the base 102 and the fin 104 of a quantum dot device 200 may be formed from a semiconductor substrate 144 and a quantum well stack 146 disposed on the semiconductor substrate 144. The quantum well stack 146 may include a quantum well layer in which a 2DEG may form during operation of the quantum dot device 200. The quantum well stack 146 may take any of a number of forms, several of which were illustrated in FIGS. 5-7 and were discussed above, which descriptions are, therefore, not repeated here.
The semiconductor substrate 144 and the quantum well stack 146 may be distributed between the base 102 and the fins 104 of the quantum dot device 200, as discussed above. This distribution may occur in any of a number of ways. For example, FIGS. 13-19 illustrate example base/fin arrangements 158 that may be used in a quantum dot device 200, in accordance with various embodiments.
In the base/fin arrangement 158 of FIG. 13, the quantum well stack 146 may be included in the fins 104, but not in the base 102. The semiconductor substrate 144 may be included in the base 102, but not in the fins 104. Manufacturing of the base/fin arrangement 158 of FIG. 13 may include fin etching through the quantum well stack 146, stopping when the semiconductor substrate 144 is reached.
In the base/fin arrangement 158 of FIG. 14, the quantum well stack 146 may be included in the fins 104, as well as in a portion of the base 102. A semiconductor substrate 144 may be included in the base 102 as well, but not in the fins 104. Manufacturing of the base/fin arrangement 158 of FIG. 14 may include fin etching that etches partially through the quantum well stack 146, and stops before the semiconductor substrate 144 is reached. FIG. 15 illustrates a particular embodiment of the base/fin arrangement 158 of FIG. 14. In the embodiment of FIG. 15, the quantum well stack 146 of FIG. 7 is used; the fins 104 include the barrier layer 154-1, the quantum well layer 152, and the barrier layer 154-2, while the base 102 includes the buffer layer 176 and the semiconductor substrate 144.
In the base/fin arrangement 158 of FIG. 16, the quantum well stack 146 may be included in the fins 104, but not the base 102. The semiconductor substrate 144 may be partially included in the fins 104, as well as in the base 102. Manufacturing the base/fin arrangement 158 of FIG. 16 may include fin etching that etches through the quantum well stack 146 and into the semiconductor substrate 144 before stopping. FIG. 17 illustrates a particular embodiment of the base/fin arrangement 158 of FIG. 16. In the embodiment of FIG. 17, the quantum well stack 146 of FIG. 7 is used; the fins 104 include the quantum well stack 146 and a portion of the semiconductor substrate 144, while the base 102 includes the remainder of the semiconductor substrate 144.
Although the fins 104 have been illustrated in many of the preceding figures as substantially rectangular with parallel sidewalls, this is simply for ease of illustration, and the fins 104 may have any suitable shape (e.g., shape appropriate to the manufacturing processes used to form the fins 104). For example, as illustrated in the base/fin arrangement 158 of FIG. 18, in some embodiments, the fins 104 may be tapered. In some embodiments, the fins 104 may taper by 3-10 nanometers in x-width for every 100 nanometers in z-height (e.g., 5 nanometers in x-width for every 100 nanometers in z-height). When the fins 104 are tapered, the wider end of the fins 104 may be the end closest to the base 102, as illustrated in FIG. 18. FIG. 19 illustrates a particular embodiment of the base/fin arrangement 158 of FIG. 18. In FIG. 19, the quantum well stack 146 is included in the tapered fins 104 while a portion of the semiconductor substrate 144 is included in the tapered fins and a portion of the semiconductor substrate 144 provides the base 102.
Synchronizing Operation of Control Circuits in Quantum Circuit Assemblies
FIG. 20 is a block diagram of an example quantum circuit assembly 300 in which synchronized operation of control circuits may be implemented, in accordance with some embodiments. As shown in FIG. 20, a quantum circuit assembly 300 may include a qubit device 310 and a control circuit assembly 320.
The qubit device 310 may include a plurality of terminals 312, shown in FIG. 20 as N terminals 312, labeled as terminals 312-1 through 312-N, where N may be any integer greater than 1. In some embodiments, the qubit device 310 may be the quantum dot device 100 or the quantum dot device 200 as described above, in which case the terminals 312 may be the gates 106/108 and/or the magnet lines 121 as described above. The qubit device 310 may further include one or more qubit components 314. For example, if the qubit device 310 is the quantum dot device 100 or the quantum dot device 200 as described above, then the one or more qubit components 314 may include one or more rows of quantum dot formation regions 111 as described above. For example, in some embodiments, the qubit device 310 may include a quantum well stack structure that includes one or more rows of quantum dot formation regions, and further comprising a plurality of terminals 312 in the form of the gates 106/108 extending to the one or more rows. The rows of quantum dot formation regions of the one or more qubit components 314 may either be defined by trenches (e.g., trenches 103 as described above) or by fins (e.g., fins 104 as described above). In case of the former, the one or more qubit components 314 may include a continuous quantum well stack that includes one or more rows of the quantum dot formation region, and the qubit device 310 may further include an insulating material provided over the continuous quantum well stack, the insulating material including a trench corresponding to each of the rows, the trench extending toward the continuous quantum well stack, and a portion of a gate metal of individual ones of the plurality of gates being at least partially in the trench, as described with reference to the quantum dot device 100. In case of the latter, the one or more qubit components 314 may include a quantum well stack shapes as one or more fins, each fin corresponding to, or including, a row of the quantum dot formation region, and the qubit device 310 may further include a gate metal of individual ones of the plurality of gates is provided over the fin, as described with reference to the quantum dot device 200.
The control circuit assembly 320 may be configured to control operation of the qubit device 310. To that end, the control circuit assembly may include a plurality of control circuits 322, configured to perform different actions to control the qubit device 310 (e.g., to apply signals to various terminals 312), the plurality of control circuits 322 are shown in FIG. 20 as K control circuits 322, labeled as control circuits 322-1 through 322-K, where K may be any integer greater than 1. For example, one or more of the plurality of control circuits 322 may be microwave circuits configured to apply microwave signals (e.g., microwave pulses) to various terminals 312, e.g., to influence the spin states of the quantum dots 142 as described above. In another example, one or more of the plurality of control circuits 322 may be baseband circuits configured to apply baseband signals (e.g., baseband pulses) to various terminals 312. For example, baseband signals may be sent through a directional coupler to a matching network attached to the source region of the SET detector. In yet another example, one or more of the plurality of control circuits 322 may be bias circuits configured to apply bias signals (e.g., DC signals) to various terminals 312, e.g., to set the operating point of various circuit components of the qubit device 310. If the qubit device 310 is a quantum dot device 100 or 200 as described above, then, in some embodiments, some of the control circuits 322 may be configured to perform actions in the form of applying signals to various gates 106/108 associated with the active row of the quantum dot formation region 111 to control formation of active quantum dots 142 in the active row of quantum dot formation region 111, while other control circuits 322 may be configured to perform actions in the form of applying signals to various gates 106/108 associated with the read row of the quantum dot formation region 111 to control formation of read quantum dots 142 in the read row of quantum dot formation region 111.
As further shown in FIG. 20, the control circuit assembly 320 may further include an event synchronization arrangement 324, configured to control the plurality of control circuits 322 in order to synchronize their operation. In general, the event synchronization arrangement 324 can enable provision of indications that a given circuit has finished performing a certain action related to controlling operation of the qubit device 310 to other circuits so that the other circuits can time their operation accordingly. For example, in some embodiments, the control circuits 322 may include a first control circuit 322-1 and a second control circuit 322-2, where the first control circuit 322-1 may be configured to perform a first action to control operation of the qubit device 310. In such embodiments, the event synchronization arrangement 324 may be configured to provide to the second control circuit 322-2 an indication that the first control circuit 322-1 performed the first action, and to configure the second control circuit 322-2 to perform a second action to control operation of the qubit device 310 in response to the second control circuit 322-2 receiving said indication.
Some example implementations of the event synchronization arrangement 324 are shown in FIGS. 21-22, providing block diagrams of example control circuit assemblies 320 to synchronize operation of control circuits in a quantum circuit assembly 300, in accordance with various embodiments. FIGS. 21-22 illustrate examples with four control circuits 322-k (i.e., k is an integer between 1 and 4 in this case, representing an individual control circuit 322) that may need to be synchronized between one another. For example, the first control circuit 322-1 may be a microwave control circuit, the second control circuit 322-2 may be a pulse control circuit, the third control circuit 322-3 may be a stimulation control circuit, and the fourth control circuit 322-4 may be a readout control circuit. However, the descriptions of FIGS. 21-22 are applicable to any other number K of the control circuits 322. As further shown in FIGS. 21-22, in some embodiments, the event synchronization arrangement 324 of the control circuit assembly 320 may include a pair of event lines 424 associated with each of the control circuits 322. The event lines for different circuits are labeled in FIGS. 21-22 with a dash after the reference numeral “424” and with the first digit corresponding to the number k of the control circuit 322 and the second digit being either “1” to represent the first event line of the pair or “2” to represent the second event line of the pair. For example, the first control circuit 322-1 may be associated with a first event line 424-11 and a second event line 424-12, the second control circuit 322-2 may be associated with a first event line 424-21 and a second event line 424-22, and so on. The first event line 424-k1 may be a communication line that enables the control circuit 322-k to receive an indication (an event) that another control circuit 322 performed its action, while the second event line 424-k2 may be a communication line that enables the control circuit 322-k to provide an indication (an event) to another control circuit 322 that the control circuit 322-k performed its action. In this way, every control circuit 322 may exchange indications of performed actions with other circuits. In various embodiments, any of the event lines 424 may be implemented as any suitable communication lines, such as electrical communication lines, optical communication lines, etc., with communications following any suitable protocol and format.
In some embodiments, the event synchronization arrangement 324 may include only one of the event lines 424 for at least some of the control circuits 322. For example, some control circuits 322 may be configured to provide an indication of their action to other control circuits 322 but do not need to receive such indications from other circuits. In some embodiments, the event synchronization arrangement 324 may further include control logic to configure the control circuits 322 to perform their respective actions and/or to provide indications to or receive indications from other control circuits 322 over the respective event lines 424. Such control logic is not shown in FIGS. 21-22 but may be implemented as, e.g., a non-quantum processing device 2028 shown in FIG. 33.
FIG. 21 illustrates an embodiment where the control circuits 322 and the event lines 424 of the event synchronization arrangement 324 may all be included within a single module 402, whereas FIG. 22 illustrates an embodiment where the control circuits 322 may be distributed, in any suitable manner, between a plurality of modules 402 (e.g., two modules 402 as shown in FIG. 22) and the event lines 424 of the event synchronization arrangement 324 may extend between the different modules 402. In some embodiments, a module 402 may be a substrate/die/chip, in which case various control circuits 322 and event lines 424 may be provided as individual circuits on the substrate/die/chip. In some embodiments, the module 402 may be an IC package, in which case various control circuits 322 may be implemented in one or more individual dies/chips coupled to a package substrate or a circuit board of the IC package. In some embodiments, the module 402 may be a hermetically sealed module that includes multiple IC packages, in which case various control circuits 322 may be implemented in one or more individual dies/chips coupled to a package substrate or a circuit board of the one or more IC packages.
FIG. 23 is a flow diagram of a method 500 for operating a control circuit 322 in a quantum circuit assembly 300 in a manner that synchronizes the control circuit with other control circuits, in accordance with some embodiments. In some embodiments, the event synchronization arrangement 324 may be configured to operate the control circuit 322 according to the method 500. As shown in FIG. 23, the method 500 may start with a process 502 that includes the control circuit 322 performing an action to control the qubit device 310. The method 500 may then include one or both of a process 504, where the control circuit 322 sends an event (e.g., an indication) to another control circuit that the control circuit 322 performed the action in the process 502, and a process 506, where the control circuit 322 waits to receive an event (e.g., an indication) from another control circuit that the other control circuit performed an action. A given control circuit 322-k may send an event in the process 504 using the event line 424-k2 as described above, and may receive an event in the process 506 using the event line 424-k1 as described above. In case the method 500 does include the process 506, the method 500 may further include a process 508 in which the control circuit 322 waits for a time period after receipt of the event in the process 506. After that, the method 500 may repeat again, as is illustrated in FIG. 5 with an arrow from the process 508 to the process 502. In some embodiments, such iterative nature of the method 500 may be optional for at least some actions, some control circuits 322, and/or some time periods during the operation of the control circuits 322.
FIGS. 24-27 are example timing diagrams for different scenarios of synchronizing operation of control circuits in a quantum circuit assembly, in accordance with various embodiments. Each of FIGS. 24-27 illustrates processes of the method 500 performed by different control circuits, as a function of time (the time increasing along the horizontal axis), where the processes of the method 500 performed by a given control circuit 322-k are shown as processes 502-k, 504-k, 506-k, and 508-k.
FIG. 24 illustrates an embodiment where the first control circuit 322-1 is configured to perform an action in the process 502-1, and subsequently, in the process 504-1, send an indication to the second control circuit 322-2 that it performed the action in the process 502-1. While the first control circuit 322-1 is performing an action in the process 502-1 and sending an event in the process 504-1, the second control circuit 322-2 is waiting for the event, i.e., is performing the process 506-2. FIG. 24 illustrates that the end of the process 506-2, indicative of the time the second control circuit 322-2 received the indication sent by the first control circuit 322-1, occurs later in time than the end of the process 504-1, with the time difference t12, labeled in FIG. 24, being the time that it takes for the second control circuit 322-2 to receive the indication sent by the first control circuit 322-1. FIG. 24 further illustrates that, once the second control circuit 322-2 received the indication sent by the first control circuit 322-1, the second control circuit 322-2 performs its action in the process 502-2, after that the second control circuit 322-2 enters the waiting period of the process 506-2 again. In the meantime, after the first control circuit 322-1 sent an indication to the second control circuit 322-2, in the process 504-1, it may be configured to perform the action again, in the next iteration of the process 502-1, and so on. Thus, FIG. 24 illustrates an embodiment where the first control circuit 322-1 is configured to iterate a sequence of performing an action and sending an indication to the second control circuit 322-2, while the second control circuit 322-2 is configured to wait for the receipt of the indication from the first control circuit 322-1 and then perform its action in response to receiving said indication, and so on.
FIG. 25 illustrates an embodiment similar to that of FIG. 24, except that now the second control circuit 322-2 is also configured to send an indication, in the process 504-2, to the first control circuit 322-1 that it performed the action in the process 502-2, after which the second control circuit 322-2 enters the waiting period of the process 506-2. Correspondingly, after the first control circuit 322-1 performed the action in the process 502-1 for the first time and sent an indication in the process 504-1, it is configured to enter the waiting period of the process 506-1 to wait to receive an indication sent by the second control circuit 322-2 before performing the action in the next iteration of the process 502-1. FIG. 25 illustrates that the end of the process 506-1, indicative of the time the first control circuit 322-1 received the indication sent by the second control circuit 322-2, occurs later in time than the end of the process 504-2, with the time difference t21, labeled in FIG. 25, being the time that it takes for the first control circuit 322-1 to receive the indication sent by the second control circuit 322-2. In general, the times t12 and t21 may, but do not have to be, equal. Thus, FIG. 25 illustrates an embodiment where the first control circuit 322-1 is configured to, first, perform an action and send an indication to the second control circuit 322-2 for the first time, and, after that, iterate a sequence of waiting for receipt of an indication from the second control circuit 322-2, performing an action upon the receipt of said indication, and sending its own indication that it performed the action to the second control circuit 322-2. On the other hand, the second control circuit 322-2 is configured to iterate a sequence of waiting for the receipt of the indication from the first control circuit 322-1, performing its action in response to receiving said indication, and sending its own indication that it performed the action to the first control circuit 322-1.
FIG. 26 illustrates an embodiment similar to that of FIG. 24 in the functionality of the second control circuit 322-2 and similar to that of FIG. 25 in that the first control circuit 322-1 is configured to repeat performing the action in the process 502-1 after it received an indication of another control circuit having finished its action, except that the first control circuit 322-1 is configured to provide an indication of having finished its action of the process 502-1 not only to the second control circuit 322-2 but also to the third control circuit 322-3. While the first control circuit 322-1 is performing an action in the process 502-1 and sending an event in the process 504-1, the third control circuit 322-3 is waiting for the event, i.e., is performing the process 506-3. FIG. 26 illustrates that the end of the process 506-3, indicative of the time the third control circuit 322-2 received the indication sent by the first control circuit 322-1, occurs later in time than the end of the process 504-1, with the time difference t13, labeled in FIG. 26, being the time that it takes for the third control circuit 322-3 to receive the indication sent by the first control circuit 322-1. FIG. 26 further illustrates that, once the third control circuit 322-3 received the indication sent by the first control circuit 322-1, the third control circuit 322-3 performs its action in the process 502-3, and then sends an indication, in the process 504-3, to the first control circuit 322-1 that it performed the action in the process 502-3, after which the third control circuit 322-3 enters the waiting period of the process 506-3. Correspondingly, after the first control circuit 322-1 performed the action in the process 502-1 for the first time and sent an indication in the process 504-1, it is configured to enter the waiting period of the process 506-1 to wait to receive an indication sent by the third control circuit 322-3 before performing the action in the next iteration of the process 502-1. FIG. 26 illustrates that the end of the process 506-1, indicative of the time the first control circuit 322-1 received the indication sent by the third control circuit 322-3, occurs later in time than the end of the process 504-3, with the time difference t31, labeled in FIG. 26, being the time that it takes for the first control circuit 322-1 to receive the indication sent by the third control circuit 322-3. In general, the times t13 and t31 may, but do not have to be, equal, and the times t12 and t13 may, but do not have to be, equal. Thus, FIG. 26 illustrates an embodiment where the first control circuit 322-1 is configured to, first, perform an action and send an indication to each of the second control circuit 322-2 and the third control circuit 322-3 for the first time, and, after that, iterate a sequence of waiting for receipt of an indication from the third control circuit 322-3, performing an action upon the receipt of said indication, and sending its own indication again (to each of the second control circuit 322-2 and the third control circuit 322-3) that it performed the action. On the other hand, the third control circuit 322-3 is configured to iterate a sequence of waiting for the receipt of the indication from the first control circuit 322-1, performing its action in response to receiving said indication, and sending its own indication that it performed the action to the first control circuit 322-1, while the second control circuit 322-2 is configured to iterate a sequence of waiting for the receipt of the indication from the first control circuit 322-1 and then performing its action in response to receiving said indication.
FIG. 27 illustrates an embodiment similar to that of FIG. 26, except that the third control circuit 322-3 is further configured to perform a process 508-3 in which it waits for a certain time period after receipt of an indication of the first control circuit 322-1 having performed an action before proceeding with performing its action in the process 502-3. Thus, the embodiment of FIG. 27 includes the third control circuit 322-3 performing the process 508-3 between the processes 506-3 and 502-3. Such an embodiment may be useful to, e.g., coordinate the time when the second control circuit 322-2 and the third control circuit 322-3 perform their respective actions.
Besides the examples shown in FIGS. 24-27, other embodiments of the control circuits 322 performing various processes of the method 500 are possible and are within the scope of the present disclosure. The exact arrangement of how the individual control circuits 322 perform various processes of the method 500 with respect to one another may be selected for a particular design of a qubit device 300 based on, e.g., the individual actions performed by the control circuits 322, complexity of and the timing required for routing event signals (indications) between various control circuits 322, the desired operations to be performed by the control circuits 322 in concert with one another, etc. In some embodiments, each of the processes of the method 500 may be considered to be a different mode of operation of a control circuit 322. Thus, at any given time, a control circuit 322-k may be in one of a plurality of modes 502-k, 504-k, 506-k, and 508-k, or any subset of these modes as described above with some of the processes 504, 506, and 508 being optional. In some embodiments, the control logic of the event synchronization arrangement 524 may be configured to set the modes of operation for each of the control circuits 322 and/or control that the control circuits 322 operate in the desired sequence of modes, e.g., as shown with the examples of FIGS. 24-27. The sequence of processes or modes of the method 500 in which each particular control circuit 322 is configured to operate may be stored in a memory, e.g., in the memory 2004 shown in FIG. 33, e.g., may be stored in a register address map. Thus, the event-based synchronization method for synchronizing operation of the control circuits 322 as described herein advantageously enables programmable event connectivity (i.e., programmable operation of the control circuits 322 with respect to actions of one another), easily visible in the register address map.
In some embodiments, at least some of the event lines 424 may be routed at the time of the design of the qubit device 300, and may be fixed after that (i.e., cannot be changed). In other embodiments, some or all of the event lines 424 may be established when the event connectivity of various control circuits 322 is programmed. To that end, one or more programmable crossbar routers may be used as shown in FIGS. 28-29, providing block diagrams of example control circuit assemblies 320 with one or more crossbar routers 624 to synchronize operation of control circuits 322 in a quantum circuit assembly 300, in accordance with various embodiments. A crossbar router 624 may be seen as a programmable switching matrix that selectively switches connectivity between various control circuits 322 to enable provision and receipt of the events/indications as described herein between the circuits 322. The one or more crossbar routers 624 may be a part of the event synchronization arrangement 324.
As shown in FIG. 28, in some embodiments, each of the control circuits 322 may be coupled to a single crossbar router 624 in that each control circuit 322 may provide an indication that it performed an action (i.e., perform the process 504 of the method 500) to another control circuit by providing it to the crossbar router 624, which will then communicate the indication to the target recipient control circuit. This means that each of the control circuits 322 is configured to receive an indication (i.e., an event that ends the process 506 of the method 500) from another control circuit 322 via the crossbar router 624. To that end, the first event line 424-k1 of a control circuit 322-k may be communicatively coupled to the crossbar router 624 so that the control circuit 322-k can receive an indication (an event) that another control circuit 322 performed its action from the crossbar router, via the first event line 424-k1. Similarly, the second event line 424-k2 of a control circuit 322-k may be communicatively coupled to the crossbar router 624 so that the control circuit 322-k can provide/send an indication (an event) that it performed its action to another control circuit 322 by sending it to the crossbar router, via the second event line 424-k2. Such directions of communications between the crossbar router 624 and the different event lines 424 of different control circuits 322 are shown in FIG. 28 with arrows.
In some embodiments, more than one crossbar routers 624 may be used in the control circuit assembly 320, with different control circuits 322 communicatively coupled as described above to one of the crossbar routers 624 and different crossbar routers 624 being communicatively coupled to one another. One such example is shown in FIG. 29, illustrating an embodiment similar to that shown in FIG. 22, except that each of the modules 402 further includes a respective crossbar router 624, shown as a first crossbar router 624-1 associated with (e.g., included in) the first module 402-1 and a second crossbar router 624-2 associated with (e.g., included in) the second module 402-2. Within a given module 402, each of the control circuits 322 may be communicatively coupled to the respective crossbar router 624 in the manner described above with reference to FIG. 28. Then the first crossbar router 624-1 and the second crossbar router 624-2 may be communicatively coupled to one another to be able to communicate (i.e., send and receive, as shown in FIG. 29 with a double-arrow between these routers) indications (events) provided to them by their respective control circuits 322. Such an arrangement further increases programmability of the communication channels for exchanging events between different control circuits 322 that may be included in different modules 402.
In some embodiments when the event connectivity between individual control circuits 322 is not predetermined but is programmed for a given collection of the control circuits 322 by virtue of using one or more crossbar routers 624 as described above, it may be desirable to find out how long it takes for an event sent by one control circuit to reach another circuit and vice versa (i.e., to determine the durations of time periods such as t12, t21, t13, and t31, described above). In such embodiments, the control circuit assembly 320 may be configured to calibrate the control circuits 322 to determine these times as is shown in FIG. 30.
FIG. 30 is a flow diagram of a method 700 for calibrating control circuits 322 of a quantum circuit assembly 300, in accordance with some embodiments. For example, the method 700 may be performed by the control logic of the event synchronization arrangement 324.
As shown in FIG. 30, the method 700 may begin with a process 702, in which the event lines 424 of different control circuits 322 are configured. The process 702 may include communicatively coupling various ones of the event lines 424 to respective crossbar routers 624 and, possibly, communicatively coupling multiple crossbar routers 624 together so that events may be exchanged between the control circuits 322 via one or more crossbar routers 624, e.g., as described with reference to FIGS. 28-29. In a process 704, an initial value identifying a particular control circuit 322 of K control circuits 322 is set, e.g., k=1, identifying the first control circuit 322-1 as the first circuit to be calibrated. In a process 706, a crossbar router 624 that is coupled to the first event line 424-k1 of the control circuit 322-k sends an event/indication to the control circuit 322-k, which the control circuit 322-k may loop back to the crossbar router via the second event line 424-k2 in a process 708. The time of the processes 706 and 708 allows the crossbar router 624 coupled to the control circuit 322-k to determine, in a process 710, the time it takes for the crossbar router 624 to send events to and receive events from the control circuit 322-k. The method 700 may then include a process 712 in which it is decided whether another control circuit 322 should be calibrated in a similar manner. If so, then the method 700 may proceed to a process 716 where k is incremented to identify the next control circuit 322 for calibration, and the method 700 repeats starting at the process 706 for the next control circuit 322 (i.e., for the next value of k). Otherwise (i.e., if no other control circuits need to be calibrated), the method 700 may proceed to a process 714 that finishes the calibration.
The method 700 may advantageously enable self-calibration of communicative connections to/from various control circuits 322 both on chip/die 402 and between multiple modules 402. Once the delay in sending and receiving events between various control circuits 322 has been determined in this manner, it can be compensated for during instruction scheduling (i.e., when programming the order and the timing of the sequences of the processes of the method 500 for various control circuits 322), if needed. In some embodiments, in the calibration mode of the method 700, every control circuit 322 may loops the incoming events back to the crossbar router 624 and the crossbar router 624 can measure the propagation delay with resolution of about one clock cycle. This means that the higher the calibration clock frequency, the lower is the resolution error, e.g., for a 1 GHz clock the error is about 1 nanoseconds (ns). The method 700 may work substantially identically within a system-on-a-chip (SOC) and across different SOCs (e.g., within a single module 402 and across multiple modules 402).
Example Devices and Systems
Quantum circuit assemblies with synchronized operation of control circuits as described above may be implemented using any kind of qubit devices or be included in any kind of quantum processing devices/structures. Some examples of such devices/structures are illustrated in FIGS. 31A-31B, 32, and 33.
FIGS. 31A-31B are top views of a wafer 1100 and dies 1102 that may be formed from the wafer 1100, according to some embodiments of the present disclosure. Dies 1102 may include any of the quantum circuit assemblies with synchronized operation of control circuits disclosed herein, or portions thereof, any embodiments of the quantum circuit assembly 300 or a portion thereof, or any combination of various embodiments of the quantum circuit assembly 300 or a portion thereof. The wafer 1100 may include semiconductor material and may include one or more dies 1102 having conventional and quantum circuit device elements formed on a surface of the wafer 1100. Each of the dies 1102 may be a repeating unit of a semiconductor product that includes any suitable conventional and/or quantum circuit qubit device. After the fabrication of the semiconductor product is complete, the wafer 1100 may undergo a singulation process in which each of the dies 1102 is separated from one another to provide discrete “chips” of the semiconductor product. A die 1102 may include, or be included in, a quantum circuit component. In some embodiments, the wafer 1100 or the die 1102 may include a memory device (e.g., a static random-access memory (SRAM) device), a logic device (e.g., AND, OR, NAND, or NOR gate), or any other suitable circuit element. Multiple ones of these devices may be combined on a single die 1102. For example, a memory array formed by multiple memory devices may be formed on a same die 1102 as a processing device (e.g., the processing device 2002 of FIG. 33) or other logic that is configured to store information in the memory devices or execute instructions stored in the memory array.
FIG. 32 is a cross-sectional side view of a device assembly 1200 that may include any of the embodiments of the quantum circuit assemblies with synchronized operation of control circuits as disclosed herein. The device assembly 1200 includes a number of components disposed on a circuit board 1202. The device assembly 1200 may include components disposed on a first face 1240 of the circuit board 1202 and an opposing second face 1242 of the circuit board 1202; generally, components may be disposed on one or both faces 1240 and 1242.
In some embodiments, the circuit board 1202 may be a printed circuit board (PCB) including multiple metal layers separated from one another by layers of dielectric material and interconnected by electrically conductive vias. Any one or more of the metal layers may be formed in a desired circuit pattern to route electrical signals (optionally in conjunction with other metal layers) between the components coupled to the circuit board 1202. In other embodiments, the circuit board 1202 may be a package substrate or flexible board.
The IC device assembly 1200 illustrated in FIG. 32 may include a package-on-interposer structure 1236 coupled to the first face 1240 of the circuit board 1202 by coupling components 1216. The coupling components 1216 may electrically and mechanically couple the package-on-interposer structure 1236 to the circuit board 1202, and may include solder balls (as shown in FIG. 32), male and female portions of a socket, an adhesive, an underfill material, and/or any other suitable electrical and/or mechanical coupling structure.
The package-on-interposer structure 1236 may include a package 1220 coupled to an interposer 1204 by coupling components 1218. The coupling components 1218 may take any suitable form for the application, such as the forms discussed above with reference to the coupling components 1216. Although a single package 1220 is shown in FIG. 32, multiple packages may be coupled to the interposer 1204; indeed, additional interposers may be coupled to the interposer 1204. The interposer 1204 may provide an intervening substrate used to bridge the circuit board 1202 and the package 1220. The package 1220 may be a quantum circuit device package as described herein, e.g., a package including any of the quantum circuit assemblies with synchronized operation of control circuits as described herein; or may be a conventional IC package, for example. Generally, the interposer 1204 may spread a connection to a wider pitch or reroute a connection to a different connection. For example, the interposer 1204 may couple the package 1220 (e.g., a die) to a ball grid array (BGA) of the coupling components 1216 for coupling to the circuit board 1202. In the embodiment illustrated in FIG. 32, the package 1220 and the circuit board 1202 are attached to opposing sides of the interposer 1204; in other embodiments, the package 1220 and the circuit board 1202 may be attached to a same side of the interposer 1204. In some embodiments, three or more components may be interconnected by way of the interposer 1204.
The interposer 1204 may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In some embodiments, the interposer 1204 may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-V and group IV materials. The interposer 1204 may include metal interconnects 1208 and vias 1210, including but not limited to through-silicon vias (TSVs) 1206. The interposer 1204 may further include embedded devices 1214, including both passive and active devices. Such devices may include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, electrostatic discharge (ESD) devices, and memory devices. More complex devices such as radio frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and microelectromechanical systems (MEMS) devices may also be formed on the interposer 1204. The package-on-interposer structure 1236 may take the form of any of the package-on-interposer structures known in the art.
The device assembly 1200 may include a package 1224 coupled to the first face 1240 of the circuit board 1202 by coupling components 1222. The coupling components 1222 may take the form of any of the embodiments discussed above with reference to the coupling components 1216, and the package 1224 may take the form of any of the embodiments discussed above with reference to the package 1220. The package 1224 may be a package including any quantum circuit assemblies with synchronized operation of control circuits disclosed herein; or may be a conventional IC package, for example.
The device assembly 1200 illustrated in FIG. 32 includes a package-on-package structure 1234 coupled to the second face 1242 of the circuit board 1202 by coupling components 1228. The package-on-package structure 1234 may include a package 1226 and a package 1232 coupled together by coupling components 1230 such that the package 1226 is disposed between the circuit board 1202 and the package 1232. The coupling components 1228 and 1230 may take the form of any of the embodiments of the coupling components 1216 discussed above, and the packages 1226 and 1232 may take the form of any of the embodiments of the package 1220 discussed above. Each of the packages 1226 and 1232 may be a qubit device package as described herein or may be a conventional IC package, for example.
FIG. 33 is a block diagram of an example quantum computing device 2000 that may include any of the quantum circuit assemblies with synchronized operation of control circuits as disclosed herein, or any combinations of various embodiments of such quantum circuit assemblies or portions thereof. Several components are illustrated in FIG. 33 as included in the quantum computing device 2000, but any one or more of these components may be omitted or duplicated, as suitable for the application. In some embodiments, some or all of the components included in the quantum computing device 2000 may be attached to one or more PCBs (e.g., a motherboard), and may be included in, or include, any of the quantum circuit assemblies with synchronized operation of control circuits as described herein. In some embodiments, various ones of these components may be fabricated onto a single SOC die. Additionally, in various embodiments, the quantum computing device 2000 may not include one or more of the components illustrated in FIG. 33, but the quantum computing device 2000 may include interface circuitry for coupling to the one or more components. For example, the quantum computing device 2000 may not include a display device 2006, but may include display device interface circuitry (e.g., a connector and driver circuitry) to which a display device 2006 may be coupled. In another set of examples, the quantum computing device 2000 may not include an audio input device 2018 or an audio output device 2008, but may include audio input or output device interface circuitry (e.g., connectors and supporting circuitry) to which an audio input device 2018 or audio output device 2008 may be coupled.
The quantum computing device 2000 may include a cooling apparatus 2024. The cooling apparatus 2024 may maintain a quantum processing device 2026 of the quantum computing device 2000, in particular the qubit devices as described herein, at a predetermined low temperature during operation to avoid qubit decoherence and to reduce the effects of scattering in the quantum processing device 2026. In some embodiments, a non-quantum processing device 2028 of the quantum computing device 2000 (and various other components of the quantum computing device 2000) may not be cooled by the cooling apparatus 2030 and may instead operate at room temperature.
The quantum computing device 2000 may include a processing device 2002 (e.g., one or more processing devices). As used herein, the term “processing device” or “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. The processing device 2002 may include a quantum processing device 2026 (e.g., one or more quantum processing devices), and a non-quantum processing device 2028 (e.g., one or more non-quantum processing devices). The quantum processing device 2026 may include any of the quantum circuit assemblies with synchronized operation of control circuits as disclosed herein, and may perform data processing by performing operations on the qubits that may be generated in the quantum circuit assemblies 300, and monitoring the result of those operations. For example, as discussed above, different qubits may be allowed to interact, the quantum states of different qubits may be set or transformed, and the quantum states of different qubits may be read. The quantum processing device 2026 may be a universal quantum processor, or specialized quantum processor configured to run one or more quantum algorithms. In some embodiments, the quantum processing device 2026 may execute algorithms that are particularly suitable for quantum computers, such as cryptographic algorithms that utilize prime factorization, encryption/decryption, algorithms to optimize chemical reactions, algorithms to model protein folding, etc. The quantum processing device 2026 may also include support circuitry to support the processing capability of the quantum processing device 2026, such as input/output channels, multiplexers, signal mixers, quantum amplifiers, and analog-to-digital converters.
As noted above, the processing device 2002 may include a non-quantum processing device 2028. In some embodiments, the non-quantum processing device 2028 may provide peripheral logic to support the operation of the quantum processing device 2026. For example, the non-quantum processing device 2028 may control the performance of a read operation, control the performance of a write operation, control the clearing of quantum bits, etc. The non-quantum processing device 2028 may also perform conventional computing functions to supplement the computing functions provided by the quantum processing device 2026. For example, the non-quantum processing device 2028 may interface with one or more of the other components of the quantum computing device 2000 (e.g., the communication chip 2012 discussed below, the display device 2006 discussed below, etc.) in a conventional manner, and may serve as an interface between the quantum processing device 2026 and conventional components. The non-quantum processing device 2028 may include one or more digital signal processors (DSPs), application-specific ICs (ASICs), central processing units (CPUs), graphics processing units (GPUs), cryptoprocessors (specialized processors that execute cryptographic algorithms within hardware), server processors, or any other suitable processing devices.
The quantum computing device 2000 may include a memory 2004, which may itself include one or more memory devices such as volatile memory (e.g., dynamic random-access memory (DRAM)), nonvolatile memory (e.g., read-only memory (ROM)), flash memory, solid-state memory, and/or a hard drive. In some embodiments, the states of qubits in the quantum processing device 2026 may be read and stored in the memory 2004. In some embodiments, the memory 2004 may include memory that shares a die with the non-quantum processing device 2028. This memory may be used as cache memory and may include embedded dynamic random-access memory (eDRAM) or spin transfer torque magnetic random-access memory (STT-M RAM).
In some embodiments, the quantum computing device 2000 may include a communication chip 2012 (e.g., one or more communication chips). For example, the communication chip 2012 may be configured for managing wireless communications for the transfer of data to and from the quantum computing device 2000. The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data using modulated electromagnetic radiation through a nonsolid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not.
The communication chip 2012 may implement any of a number of wireless standards or protocols, including but not limited to Institute for Electrical and Electronic Engineers (IEEE) standards including Wi-Fi (IEEE 802.11 family), IEEE 802.16 standards (e.g., IEEE 802.16-2005 Amendment), Long-Term Evolution (LTE) project along with any amendments, updates, and/or revisions (e.g., advanced LTE project, ultramobile broadband (UMB) project (also referred to as “3GPP2”), etc.). IEEE 802.16 compatible Broadband Wireless Access (BWA) networks are generally referred to as WiMAX networks, an acronym that stands for Worldwide Interoperability for Microwave Access, which is a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. The communication chip 2012 may operate in accordance with a Global System for Mobile Communication (GSM), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), High Speed Packet Access (HSPA), Evolved HSPA (E-HSPA), or LTE network. The communication chip 2012 may operate in accordance with Enhanced Data for GSM Evolution (EDGE), GSM EDGE Radio Access Network (GERAN), Universal Terrestrial Radio Access Network (UTRAN), or Evolved UTRAN (E-UTRAN). The communication chip 2012 may operate in accordance with Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Digital Enhanced Cordless Telecommunications (DECT), Evolution-Data Optimized (EV-DO), and derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The communication chip 2012 may operate in accordance with other wireless protocols in other embodiments. The quantum computing device 2000 may include an antenna 2022 to facilitate wireless communications and/or to receive other wireless communications (such as AM or FM radio transmissions).
In some embodiments, the communication chip 2012 may manage wired communications, such as electrical, optical, or any other suitable communication protocols (e.g., the Ethernet). As noted above, the communication chip 2012 may include multiple communication chips. For instance, a first communication chip 2012 may be dedicated to shorter-range wireless communications such as Wi-Fi or Bluetooth, and a second communication chip 2012 may be dedicated to longer-range wireless communications such as global positioning system (GPS), EDGE, GPRS, CDMA, WiMAX, LTE, EV-DO, or others. In some embodiments, a first communication chip 2012 may be dedicated to wireless communications, and a second communication chip 2012 may be dedicated to wired communications.
The quantum computing device 2000 may include battery/power circuitry 2014. The battery/power circuitry 2014 may include one or more energy storage devices (e.g., batteries or capacitors) and/or circuitry for coupling components of the quantum computing device 2000 to an energy source separate from the quantum computing device 2000 (e.g., AC line power).
The quantum computing device 2000 may include a display device 2006 (or corresponding interface circuitry, as discussed above). The display device 2006 may include any visual indicators, such as a heads-up display, a computer monitor, a projector, a touchscreen display, a liquid crystal display (LCD), a light-emitting diode display, or a flat panel display, for example.
The quantum computing device 2000 may include an audio output device 2008 (or corresponding interface circuitry, as discussed above). The audio output device 2008 may include any device that generates an audible indicator, such as speakers, headsets, or earbuds, for example.
The quantum computing device 2000 may include an audio input device 2018 (or corresponding interface circuitry, as discussed above). The audio input device 2018 may include any device that generates a signal representative of a sound, such as microphones, microphone arrays, or digital instruments (e.g., instruments having a musical instrument digital interface (MIDI) output).
The quantum computing device 2000 may include a GPS device 2016 (or corresponding interface circuitry, as discussed above). The GPS device 2016 may be in communication with a satellite-based system and may receive a location of the quantum computing device 2000, as known in the art.
The quantum computing device 2000 may include an other output device 2010 (or corresponding interface circuitry, as discussed above). Examples of the other output device 2010 may include an audio codec, a video codec, a printer, a wired or wireless transmitter for providing information to other devices, or an additional storage device.
The quantum computing device 2000 may include an other input device 2020 (or corresponding interface circuitry, as discussed above). Examples of the other input device 2020 may include an accelerometer, a gyroscope, a compass, an image capture device, a keyboard, a cursor control device such as a mouse, a stylus, a touchpad, a bar code reader, a Quick Response (QR) code reader, any sensor, or a radio frequency identification (RFID) reader.
The quantum computing device 2000, or a subset of its components, may have any appropriate form factor, such as a hand-held or mobile computing device (e.g., a cell phone, a smart phone, a mobile internet device, a music player, a tablet computer, a laptop computer, a netbook computer, an ultrabook computer, a personal digital assistant (PDA), an ultramobile personal computer, etc.), a desktop computing device, a server or other networked computing component, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a vehicle control unit, a digital camera, a digital video recorder, or a wearable computing device.
Select Examples
The following paragraphs provide examples of various ones of the embodiments disclosed herein.
Example 1 provides a quantum circuit assembly that includes a quantum dot device and a control circuit assembly. The quantum dot device includes a quantum well stack structure that includes a row of a quantum dot formation region, and further including a plurality of gates extending to the row. The control circuit assembly is configured to control operation of the quantum dot device and includes a plurality of control circuits and an event synchronization arrangement. The control circuits include a first control circuit, configured to perform a first action to control operation of the quantum dot device, and a second control circuit configured to perform a second action to control operation of the quantum dot device. The event synchronization arrangement is configured to control operation of the plurality of control circuits to provide to the second control circuit an indication that the first control circuit performed the first action, and to configure the second control circuit to perform a second action to control operation of the quantum dot device in response to receiving the indication that the first control circuit performed the first action.
Example 2 provides the quantum circuit assembly according to example 1, where the quantum well stack structure includes a continuous quantum well stack that includes the row of the quantum dot formation region, the quantum dot device further includes an insulating material provided over the continuous quantum well stack, the insulating material includes a trench corresponding to the row, the trench extends toward the continuous quantum well stack, and a portion of a gate metal of individual ones of the plurality of gates is provided at least partially in the trench.
Example 3 provides the quantum circuit assembly according to example 2, where a gate dielectric is provided at a bottom of the trench between the gate metal and the continuous quantum well stack.
Example 4 provides the quantum circuit assembly according to example 1, where the quantum well stack structure includes a quantum well stack in a shape of a fin, the fin includes the row of the quantum dot formation region, and a gate metal of individual ones of the plurality of gates is provided over the fin.
Example 5 provides the quantum circuit assembly according to example 4, where a gate dielectric is provided between the gate metal and the fin.
Example 6 provides the quantum circuit assembly according to any one of the preceding examples, where at least one of the first action and the second action includes applying one or more signals to one or more of the plurality of gates of the quantum dot device.
Example 7 provides the quantum circuit assembly according to example 6, where the one or more signals include one or more microwave signals.
Example 8 provides the quantum circuit assembly according to example 6, where the one or more signals include one or more baseband signals.
Example 9 provides the quantum circuit assembly according to any one of examples 6-8, where the one or more signals include one or more signal pulses.
Example 10 provides the quantum circuit assembly according to any one of the preceding examples, where the row of the quantum dot formation region is a first row of the quantum dot formation region, the plurality of gates is a first plurality of gates, the quantum dot device further includes a second row of the quantum dot formation region and a second plurality of gates extending to the second row, the first action includes applying one or more signals to one or more of the first plurality of gates of the quantum dot device, and the second action includes applying one or more signals to one or more of the first plurality of gates of the quantum dot device.
Example 11 provides the quantum circuit assembly according to example 10, where the first row of the quantum dot formation region is an active row of the quantum dot formation region, and the second row of the quantum dot formation region is a read row of the quantum dot formation region.
Example 12 provides the control circuit assembly according to any one of the preceding examples, where the event synchronization arrangement is to configure the second control circuit to operate in one of a plurality of modes, where the plurality of modes of the second control circuit includes a first mode and a second mode, in the first mode, the second control circuit is configured to perform the second action, and in the second mode, the second control circuit is configured to wait for a receipt of the indication that the first control circuit performed the first action.
Example 13 provides the quantum circuit assembly according to example 12, where the plurality of modes of the second control circuit further includes a third mode, and in the third mode, the second control circuit is configured to provide to a further control circuit of the plurality of control circuits an indication that the second control circuit performed the second action.
Example 14 provides the quantum circuit assembly according to example 13, where the further control circuit is the first control circuit.
Example 15 provides the quantum circuit assembly according to example 14, where, after performing the first action for a first time, the event synchronization arrangement is to configure the first control circuit to operate in one of a plurality modes, where the plurality of modes of the first control circuit includes a first mode and a second mode, in the first mode, the first control circuit is configured to perform the first action, in the second mode, the first control circuit is configured to wait for a receipt of the indication that the second control circuit performed the second action, and, after performing the first action for the first time, the first control circuit is configured to perform the first action in response to receiving the indication that the second control circuit performed the second action.
Example 16 provides the quantum circuit assembly according to any one of examples 12-15, where the plurality of modes of the second control circuit further includes a fourth mode, and in the fourth mode, the second control circuit is configured to wait for a time period after the receipt of the indication that the first control circuit performed the first action before the second control circuit enters the first mode to perform the second action.
Example 17 provides the quantum circuit assembly according to any one of the preceding examples, where the event synchronization arrangement includes a plurality of communication lines to communicate one or more indications of an action performed by one or more of the plurality of control circuits.
Example 18 provides the quantum circuit assembly according to example 17, where the plurality of communication lines include electrical and/or optical communication channels.
Example 19 provides the quantum circuit assembly according to any one of examples 1-18, where two or more of the quantum dot device, the first control circuit, and the second control circuit are provided in a single die.
Example 20 provides the quantum circuit assembly according to any one of examples 1-18, where two or more of the quantum dot device, the first control circuit, and the second control circuit are provided in a single IC package.
Example 21 provides a control circuit assembly to control operation of a qubit device. The control circuit assembly includes a plurality of control circuits, including a first control circuit, to perform a first action to control operation of the qubit device, and further including a second control circuit; and an event synchronization arrangement, to control operation of the plurality of control circuits to provide to the second control circuit an indication that the first control circuit performed the first action, and to configure the second control circuit to perform a second action to control operation of the qubit device in response to receiving the indication that the first control circuit performed the first action.
Example 22 provides the control circuit assembly according to example 21, where the event synchronization arrangement is to configure the second control circuit to operate in one of a plurality of modes, where the plurality of modes of the second control circuit includes a first mode and a second mode, in the first mode, the second control circuit is configured to perform the second action, and, in the second mode, the second control circuit is configured to wait for a receipt of the indication that the first control circuit performed the first action.
Example 23 provides the control circuit assembly according to example 22, where the plurality of modes of the second control circuit further includes a third mode, and, in the third mode, the second control circuit is configured to provide to a further control circuit of the plurality of control circuits an indication that the second control circuit performed the second action.
Example 24 provides the control circuit assembly according to example 23, where the further control circuit is the first control circuit.
Example 25 provides the control circuit assembly according to example 24, where, after performing the first action for a first time, the event synchronization arrangement is to configure the first control circuit to operate in one of a plurality modes, where the plurality of modes of the first control circuit includes a first mode and a second mode, in the first mode, the first control circuit is configured to perform the first action, in the second mode, the first control circuit is configured to wait for a receipt of the indication that the second control circuit performed the second action, and, after performing the first action for the first time, the first control circuit is configured to perform the first action in response to receiving the indication that the second control circuit performed the second action.
Example 26 provides the control circuit assembly according to any one of examples 22-25, where the plurality of modes of the second control circuit further includes a fourth mode, and, in the fourth mode, the second control circuit is configured to wait for a time period after the receipt of the indication that the first control circuit performed the first action before the second control circuit enters the first mode to perform the second action.
Example 27 provides the control circuit assembly according to any one of examples 21-26, where the event synchronization arrangement includes a plurality of communication lines to communicate one or more indications of an action performed by one or more of the plurality of control circuits. In various embodiments, such communication lines may be electrical communication lines, optical communication lines, or any other type of communication lines suitable for providing indications as described herein.
Example 28 provides a method of operating a qubit device. The method includes using a first control circuit to perform a first action to control the qubit device; providing an indication to a second control circuit that the first control circuit performed the first action; and using the second control circuit to perform a second action to control the qubit device upon the second control circuit receiving the indication.
Example 29 provides the method according to example 28, where the second control circuit is configured to wait for a receipt of the indication that the first control circuit performed the first action before performing the second action.
Example 30 provides the method according to example 28, where the second control circuit is configured to perform the second action after a predefined time period following a receipt of the indication that the first control circuit performed the first action.
Example 31 provides a quantum computing device that includes a quantum processing device, where the quantum processing device includes a quantum circuit assembly according to any one of the preceding examples; a non-quantum processing device, coupled to the quantum processing device, to control voltages applied to the plurality of gates of the quantum circuit assembly of the quantum processing device; and a memory device to store data generated during operation of the quantum processing device.
Example 32 provides the quantum computing device according to example 31, further including a cooling apparatus configured to maintain the temperature of the quantum processing device below 5 degrees Kelvin.
Example 33 provides the quantum computing device according to examples 31 or 32, where the memory device is configured to store instructions for a quantum computing algorithm to be executed by the quantum processing device.
The above description of illustrated implementations of the disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. While specific implementations of, and examples for, the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize.
Patent Application
20220383170
