Patent Application
20240302590
The present disclosure relates to a quantum device and a quantum operation device.
As one of next-generation computing, a quantum computer has been researched and developed. There is a method for performing a quantum operation using a spin and a photon of a diamond color center that is a quantum element as quantum bits. This quantum operation is performed by entangling the photons emitted from diamond at a cryogenic temperature of about −270° C. The entanglement of the photons is performed via an optical waveguide including sapphire or the like that is optically coupled to a diamond optical waveguide including the color center.
Examples of the related art include: [Patent Document 1] Japanese Laid-open Patent Publication No. 2005-173162; [Patent Document 2] Japanese Laid-open Patent Publication No. 2000-208862; [Patent Document 3] U.S. Pat. No. 10,031,293; [Patent Document 4] U.S. Pat. No. 6,539,157; [Non-Patent Document 1] H. Bernien, et al., “Heralded entanglement between solid-state qubits separated by three metres”, Nature 497, 86 (2013); and [Non-Patent Document 2] Michael J. Burek, et al., “Fiber-Coupled Diamond Quantum Nanophotonic Interface”, Phys. Rev. Applied 8, 024026 (2017).
According to an aspect of the embodiments, there is provided a quantum device includes: a first optical waveguide configured to include diamond; and a second optical waveguide optically configured to be coupled to the first optical waveguide and include a material with a lower refractive index than diamond, wherein the first optical waveguide includes a first region configured to include a color center, a second region that propagates light that propagates in the first region to the second optical waveguide, and a third region connected to a side of the second region opposite to the first region and bonded to the second optical waveguide.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.
A thermal expansion coefficient of a diamond optical waveguide and a thermal expansion coefficient of an optical waveguide coupled to the diamond optical waveguide are greatly different. Therefore, even if bonding is performed with high accuracy at room temperature, when the optical waveguide is cooled to a cryogenic temperature of about −270° C., an amount of thermal deformation greatly differs. Therefore, a light propagation loss may increase due to distortion. Furthermore, these two optical waveguides are separated, and the light propagation loss may increase due to the separation.
An object of the present disclosure is to provide a quantum device and a quantum operation device that can suppress an increase in a light propagation loss caused by thermal deformation.
Hereinafter, embodiments of the present disclosure will be specifically described with reference to the attached drawings. Note that, in the present specification and drawings, components having substantially the same functional configuration are denoted with the same reference numeral, and redundant descriptions may be omitted. In the present disclosure, an X1-X2 direction, a Y1-Y2 direction, and a Z1-Z2 direction are directions orthogonal to each other. A plane including the X1-X2 direction and the Y1-Y2 direction is described as an XY plane, a plane including the Y1-Y2 direction and the Z1-Z2 direction is described as a YZ plane, and a plane including the Z1-Z2 direction and the X1-X2 direction is described as a ZX plane. Note that, for convenience, the Z1-Z2 direction is set as a vertical direction, a Z1 side is set as an upper side, and a Z2 side is set as a lower side. Furthermore, plan view is to view an object from the Z1 side, and a planar shape is a shape of the object viewed from the Z1 side.
First, a first embodiment will be described. The first embodiment relates to a quantum device. The quantum device according to the first embodiment is used for a quantum operation device such as a quantum computer, for example.
As illustrated in
The first optical waveguide 10 includes a first region 111, a second region 112, and a third region 113. The first region 111 includes a color center. The second region 112 propagates light that propagates in the first region 111 to the second optical waveguide 20. The third region 113 is connected to a side of the second region 112 opposite to the first region 111. The third region 113 is bonded to the second optical waveguide 20.
A height H1 and a width W1 of the first region 111 satisfy a single mode waveguide condition with respect to light 30 propagating in the first region 111. For example, the height H1 is 0.25 times to 0.50 times of a wavelength λ of the light 30, and the width W1 is 0.25 times to 0.60 times of the wavelength λ. In a case where the wavelength λ is 600 nm to 800 nm, the height H1 is 150 nm to 300 nm, and the width W1 may be 150 nm to 300 nm. As a specific example, in a case where the wavelength λ is 637 nm, the height H1 is 245 nm, and the width W1 is 284 nm. Note that the height H1 is a dimension of the first region 111 in a lamination direction (Z1-Z2 direction), and the width W1 is a dimension of the first region 111 in a direction (Y1-Y2 direction) perpendicular to the propagation direction (X1-X2 direction) of the light 30 in the first region 111 and the Z1-Z2 direction.
A height H2 of the second region 112 is equal to the height H1 of the first region 111, and a width W2 of the second region 112 decreases from a boundary 112A with the first region 111 toward a boundary 112B with the third region 113. A cross-sectional area of a cross section perpendicular to the X1-X2 direction of the second region 112 decreases from the boundary 112A toward the boundary 112B. For example, the width W2 and the cross-sectional area linearly decrease. The second region 112 has a trapezoidal planar shape. The width W2 of the second region 112 is a width in which a single mode cannot propagate light at the boundary 112B. For example, at the boundary 112B, the height H2 is 0.25 times to 0.50 times of the wavelength λ of the light 30, and the width W2 is 0.20 times to 0.60 times of the wavelength λ. In a case where the wavelength λ is 600 nm to 800 nm, at the boundary 112B, the height H2 is 150 nm to 300 nm, and the width W2 may be 50 nm to 150 nm. Note that the height H2 is a dimension of the second region 112 in the Z1-Z2 direction, and the width W2 is a dimension of the second region 112 in the Y1-Y2 direction. When the light 30 propagated through the first region 111 leaks to outside of the second region 112, the light 30 leaks to a region having a refractive index closest to the refractive index of diamond that is the material of the second region 112 in a surrounding region. Therefore, the light 30 is propagated to the second optical waveguide 20 including sapphire or the like.
A height H3 and a width W3 of the third region 113 are respectively equal to the height H2 and the width W2 of the second region 112 at the boundary 112B. The third region 113 has a rectangular planar shape. The light 30 hardly propagates in the third region 113. A length L3 of the third region 113 is, for example, equal to or more than 100 nm, and preferably, equal to or more than 500 nm. Note that the height H3 is a dimension of the third region 113 in the Z1-Z2 direction, the width W3 is a dimension of the third region 113 in the Y1-Y2 direction, and the length L3 is a dimension of the third region 113 in the X1-X2 direction.
In the quantum device 1 configured in this way, the light 30 emitted from the color center propagates in the first region 111, and propagates to the second optical waveguide 20 by the second region 112. The light 30 propagated to the second optical waveguide 20 is used for a quantum operation.
Furthermore, when the quantum device 1 is cooled to a cryogenic temperature of about −270° C. at the time of the quantum operation, the first optical waveguide 10 and the second optical waveguide 20 are thermally contracted depending on thermal expansion coefficients of the respective materials. At this time, since the thermal expansion coefficients of the first optical waveguide 10 and the second optical waveguide 20 are different, stress acts on an interface between the first optical waveguide 10 and the second optical waveguide 20. This stress concentrates at a front end of the first optical waveguide 10 on an X1 side, and is lowered in the X1-X2 direction as being separated from the front end. Therefore, stress acting on the second region 112 and the vicinity thereof is reduced as compared with a case where the third region 113 is not provided. Therefore, it is possible to suppress an increase in a light propagation loss caused by thermal deformation.
Next, a second embodiment will be described. The second embodiment is mainly different from the first embodiment in a configuration of the first optical waveguide.
As illustrated in
The other components are similar to those of the first embodiment.
In the second embodiment, effects similar to those of the first embodiment can be obtained. Furthermore, in the second embodiment, since the side surface of the end portion of the third region 213 on the X1 side is a curved surface, stress acting on the end portion of the third region 213 on the X1 side is easily dispersed. Therefore, separation and distortion of the third region 213 are suppressed, and propagation of the separation and the distortion generated in the third region 213 to the second region 112 can be suppressed, and it is possible to further suppress the increase in the light propagation loss.
Next, a third embodiment will be described. The third embodiment is mainly different from the second embodiment in the configuration of the first optical waveguide.
As illustrated in
The other components are similar to those of the first embodiment.
In the third embodiment, effects similar to those of the second embodiment can be obtained. Furthermore, in the third embodiment, since the height H3 of the third region 313 is smaller than the height H2 of the second region 112, it is possible to suppress light propagation of the light propagated to the second region 112 to the third region 313.
Note that a planar shape of the third region 313 may be a rectangular shape similarly to the third region 113. That is, an end surface of the third region 313 may be a plane.
Next, a fourth embodiment will be described. The fourth embodiment is mainly different from the third embodiment in the configuration of the first optical waveguide.
As illustrated in
The other components are similar to those of the third embodiment.
In the fourth embodiment, effects similar to those of the third embodiment can be obtained. Furthermore, in the fourth embodiment, since the height H2 of the second region 412 decreases from the boundary 412A toward the boundary 412B, the light 30 can be easily propagated to the second optical waveguide 20 by the second region 112.
Next, a fifth embodiment will be described. The fifth embodiment is mainly different from the fourth embodiment in a configuration below the second optical waveguide.
As illustrated in
A hollow portion 53 is formed in the cladding layer 52. The hollow portion 53 is formed on a Z2 side of (below) the second region 412. The hollow portion 53 may be formed in the cladding layer 52, from a portion of the second region 412 on the Z2 side to a portion of the third region 313 on the Z2 side.
An optical waveguide layer 20B is provided on the cladding layer 52, and a groove 20A is formed between the optical waveguide layer 20B and the second optical waveguide 20. A material of the optical waveguide layer 20B is the same as the material of the second optical waveguide 20.
In the fifth embodiment, effects similar to those of the fourth embodiment can be obtained. Furthermore, in the fifth embodiment, the second optical waveguide 20 is provided on the substrate 51 via the cladding layer 52, and the hollow portion 53 is formed in the cladding layer 52. Therefore, stress acting on the second region 412 and the vicinity thereof is relaxed by thermal deformation. Therefore, it is possible to further suppress the increase in the light propagation loss caused by the thermal deformation.
Next, a method for manufacturing the quantum device according to the fifth embodiment will be described.
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In this way, the quantum device 5 according to the fifth embodiment can be manufactured.
Note that, in the first to the fifth embodiments, the cross-sectional area of the cross section perpendicular to the X1-X2 direction of the third region does not need to be equal to a cross-sectional area S0 at the boundary between the second region and the third region and may be less than the cross-sectional area S0. Furthermore, the height H3 of the third region does not need to be equal to the height H2 at the boundary between the second region and the third region, and may be less than the height H2, and the width W3 of the third region does not need to be equal to the width W2 at the boundary between the second region and the third region and may be less than the width W2.
Next, a sixth embodiment will be described. The sixth embodiment relates to a quantum computer.
A quantum computer 6 according to the sixth embodiment includes a general-purpose computer 601, a control unit 602, and a quantum device 603. The control unit 602 controls the quantum device 603 based on a control signal from the general-purpose computer 601. As the quantum device 603, the quantum device according to any one of the first to fifth embodiments is used. The control unit 602 and the quantum device 603 are housed in a cryostat 604.
It is possible to perform a stable quantum operation by the quantum computer 6.
Next, a result of a simulation performed by the inventor of the present application will be described. In this simulation, about seven types of structures S1 to S7, a distribution of internal stress when cooling to 4 K is performed in a case of stress free at 300 K has been calculated.
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In this way, through the simulation, a result indicating that the internal stress in the second region 94B is significantly lower in the structures S3 to S7 than in the structures S1 and S2 is obtained.
Although the preferred embodiments and the like have been described in detail above, the present disclosure is not limited to the embodiments and the like described above, and various modifications and substitutions may be made to the embodiments and the like described above without departing from the scope described in claims.
All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
This application is a continuation application of International Application PCT/JP2021/042187 filed on Nov. 17, 2021 and designated the U.S., the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/042187 | Nov 2021 | WO |
| Child | 18653737 | US |
