Embodiments of the present disclosure relate to Rydberg atom based quantum computation, and more specifically, to ultrafast detection of Rydberg atoms.
In an example embodiment, the present invention is a device, comprising: at least one monochromatic light source configured to generate a first optical trap; an ensemble of particles disposed in the first optical trap, each particle of the ensemble of particles being excitable to a first Rydberg state and a second Rydberg state, the second Rydberg state having a blockade radius, each particle of the ensemble of particles being within the blockade radius of each other and within the blockade radius of an atomic qubit, the atomic qubit being a particle that is excitable to the second Rydberg state, the ensemble of particles having a first transmissivity at a first wavelength when neither any particle of the ensemble of particles nor the atomic qubit is in the second Rydberg state, the ensemble of particles having a second transmissivity at the first wavelength when the atomic qubit is in the second Rydberg state, the second transmissivity being lower than the first transmissivity; and a second monochromatic light source configured to drive each particle of the ensemble of particles into the first Rydberg state; a probe light source configured to direct a probe beam having the first wavelength to the ensemble of particles; and a photosensor configured to determine the state of the atomic qubit.
In another example embodiment, the present invention is a device, comprising: at least a first monochromatic light source configured to generate a first array of optical traps, each optical trap of the first array of optical traps having an ensemble of particles disposed therein; at least a second monochromatic light source configured to generate a second array of optical traps, wherein: each particle of each of the ensembles of particles being excitable to a first Rydberg state and a second Rydberg state, the second Rydberg state having a blockade radius, each particle of each of the ensembles of particles being within the blockade radius of the second Rydberg state of each particle in its ensemble, and of at least one optical trap of the second array of optical traps, the at least one optical trap of the second array having an atomic qubit disposed therein, the atomic qubit being a particle that is excitable to the second Rydberg state, each ensemble of particles having a first transmissivity at a first wavelength when none of its particles is in the second Rydberg state, each ensemble of particles having a second transmissivity at the first wavelength when one particle in the at least one optical trap of the second array of optical traps is in the second Rydberg state, the second transmissivity being lower than the first transmissivity, each particle of each ensemble of particles being outside the blockade radius of the second Rydberg state of each particle of any other ensemble of particles; at least a third monochromatic light source configured to drive each particle of each ensemble of particles into the first Rydberg state; a probe light source configured to direct a probe beam having the first wavelength to the ensembles of particles; and a photosensor configured to determine a quantum mechanical state of at least one particles in the ensembles of particles.
In yet another example embodiment, the present invention is a method of determining a state of an atomic qubit. The method comprises: disposing an ensemble of particles proximate to an atomic qubit, wherein: each particle of the ensemble of particles being excitable to a first Rydberg state and a second Rydberg state, the second Rydberg state having a second blockade radius, the atomic qubit being a particle that is excitable to the second Rydberg state, each particle of the ensemble of particles being within the second Rydberg state blockade radius of each other and within the second Rydberg state blockade radius of the atomic qubit, the ensemble of particles having a first transmissivity at a first wavelength when neither any particle of the ensemble of particles nor the atomic qubit is in the second Rydberg state, the ensemble of particles having a second transmissivity at the first wavelength when the atomic qubit is in the second Rydberg state, the second transmissivity being lower than the first transmissivity; driving any one particle of the ensemble of particles into the first Rydberg state; directing a probe beam having the first wavelength to the ensemble of particles; and determining the state of the atomic qubit.
population over time according to embodiments of the present disclosure.
The present disclosure provides a new approach for fast preparation, manipulation, and collective readout of an atomic Rydberg-state qubit. By making use of Rydberg blockade inside a small atomic ensemble, a single qubit is prepared within 3 μs with a success probability of Fp=0.93±0.02. The qubit is manipulated, and its state is read out in 6 μs with a single-shot fidelity of Fd=0.92±0.04. The ensemble-assisted collective optical readout speeds up state detection by a factor of 103 compared to imaging of a single atom. Qubit coherence times of 18 μs are observed, much longer than the π rotation time of 90 ns. The approaches provided herein may enable significantly faster quantum simulation in atomic arrays, as well as quantum error correction.
Fast and reliable state initialization and readout of qubits are essential requirements for implementing scalable quantum information systems. Individually-controlled highly excited Rydberg atoms are a promising platform for quantum simulation and computation. These are enabled by the strong coherent interaction between Rydberg atoms at distances exceeding several micrometers. In combination with the demonstrated ability to deterministically assemble large arrays of individual atoms, Rydberg-atom arrays may be used to simulate quantum spin models with more than 50 qubits, to perform multiple-qubit gate operations, or to create large maximally entangled states. While these quantum simulation and computation systems can operate on microsecond time scales, they could benefit substantially from faster qubit preparation and detection, as both the array preparation process and the optical state readout in alternative systems require several to many milliseconds. Moreover, fast and high-fidelity single-shot qubit readout without atom loss could enable a new generation of experiments with error mitigation, such as quantum error correction and fault tolerant quantum processing.
Alternative approaches for individual Rydberg qubit detection include state-dependent ionization and detection of the ions, a relatively fast (τ˜0.1 ms) process that has only moderate fidelity, and the state-dependent removal of atoms followed by relatively slow (τ˜10 ms) fluorescence imaging of the remaining atoms with fidelities of F≥0.95. While fast high-intensity fluorescence readout within 20 μs with single-atom resolution is possible, this method is not compatible with atomic arrays, as it does not have the necessary spatial resolution and also requires a large magnetic field. Both ion detection and fluorescence imaging are destructive readout processes, and require a new atomic array to be prepared subsequently, further limiting the cycle time of the quantum processor.
In the present disclosure, high-fidelity preparation, manipulation and detection of a single-Rydberg-atom qubit (not a collective state) inside an atomic ensemble is provided on the microsecond time scale. Starting with N˜400 trapped ultracold 87Rb atoms, a qubit is prepared between the Rydberg states |r′≡|91P3/2, mj=3/2
and |r
≡92S1/2, mj=1/2
. Qubit rotations are performed with a loss of contrast δC≤2×10−3 per 2π pulse. The state is read out optically. Harnessing the collective effect of Rydberg blockade, the state preparation and detection are performed in Tp=3 μs and Td=6 μs with fidelities of Fp=0.93±0.02 and Fd=0.92±0.04, respectively. The measured qubit coherence time of τc=(15±5) μs is much longer than the π rotation time of 90 ns.
It should be understood that the methods and devices described herein can employ atoms other than Rb, and that more than one species of atoms can be used. The Rydberg blockade is the source of the enhanced detection and it is not unique to Rb atoms. In an example embodiment, a combination of two different Alkali earth atoms can be used that have similar energy spacing to create a Rydberg blockade radius across species. An example of this is a Cs—Rb Rydberg blockade (see, I. I. Beterov and M. Saffman Phys. Rev. A 92, 042710 (2015)). The use of such a combination would prevent excitation cross talk between the ensemble and the target qubit. The different atomic species require different laser wavelengths to excite to the Rydberg state. Methods and devices described herein allow for the independent manipulation of atomic species.
The approaches provided herein harness collective phenomena for speeding up both state preparation and detection. The preparation is accomplished by application of an appropriate laser pulse to an ensemble of N atoms, such that any atom can be excited to the Rydberg state, yielding N times faster excitation of the first atom to the Rydberg state than for a single atom, while the preparation of a single excitation is ensured by the Rydberg blockade mechanism. Similarly, the signal-to-noise ratio in optical detection is collectively enhanced by a factor of about N, that is, depending on the state of the single-atom Rydberg qubit, the absorption of probe light by all of the N atoms in the ensemble is simultaneously switched on or off.
Referring to through a three-photon process involving the preparation beam (Ωp, 101), the control beam (Ωc, 102), and a microwave field (ΩMW, 103). The detunings from the two intermediate states are Δe=δr=2π×100 MHz. The preparation of a single atom in |r′
is ensured by the strong interaction between two atoms in |r′
. The values of detuning from the two intermediate states need not be equal to each other; this condition enables using the same laser frequency for the control beam during detection as described further below.
The values of detuning and Rabi frequencies during the preparation step can, in some embodiments, be optimized to ensure that the following three conditions are satisfied:
Alternatively, a two photon process can be used in which two distinct optical Rydberg wavelengths are used to couple to distinct Rydberg states. Examples of Rydberg states are |r=92S and |r′=91S
, which have the energy difference of ΔE=9.5 GHz.
. The waist size of the control beam 102 is configured to uniformly illuminate the ensemble 104. The waist size of the probe beam 105 is configured to be smaller than and ideally centered on the ensemble 104. Under conditions of electromagnetically induced transparency (EIT) (Δe=δr=0), high transmission through the atomic medium results in a large number of detected photons (left detail). On the other hand, if the second Rydberg state |r′
is populated by an atomic qubit 106 (right detail), then the strong interaction between |r
and |r′
removes the EIT condition, resulting in a significant reduction of transmitted photon number due to absorption by the ensemble. The interaction Vrr, contains both dipolar-exchange and van-der-Waals components.
As illustrated in r2
)} ≈6 μm containing typically N˜400 laser-cooled 87Rb atoms is prepared inside a two-beam optical dipole trap with waist sizes w1=10 μm and w2=20 μm. The atoms are optically pumped into the hyperfine and magnetic sublevel |g
≡|5S1/2, F=2, mF=2
that is coupled via a two-photon process involving the transitions |g
↔|e
≡|5P3/2, F=3, mF=3
(preparation beam Ωp) and |e
↔|r
(control beam Ωc) to the Rydberg state |r
≡|92S1/2, mj=1/2
When the two-photon transition is resonant with the intermediate state (Δe=0, see
, then the ensemble 104 exhibits a high (first) transmissivity of the probe beam 105 on EIT resonance, while, as shown in
, then the ensemble 104 has a low (second) transmissivity of the probe beam 105, lower than the first transmissivity. A photosensor 107 determines the state of the atomic qubit 106. In one embodiment, as shown in
In another embodiment, as shown in
To prepare a single atom in the Rydberg state |r′≡|91P3/2, mj=3/2) inside the ensemble, the probe laser and microwave field are detuned by Δe/(2π)=δr/(2π)=100 MHz from their respective transitions, and in combination with the control field drive a three-photon transition |g
↔|e
↔|r
↔|r′
(see
r2
)}=8.4 μm between any two atoms in the ensemble. This ensures that excitations of two or more atoms to the Rydberg state |r′
are suppressed.
Referring to ) and absence of an atom in Rydberg state |r′
, respectively. The solid lines in
assumes random sudden ionization of the Rydberg atom in |r′
(sudden decay of the slow-light polariton into a Rydberg state) at a rate 0.035 μs−1 (0.015 μs−1). The dashed line indicates the detection threshold that equalizes the errors for misidentifying the underlying two states. The control Rabi frequency is Ωc/(2π)=25 MHz, and the probabilities for collecting and detecting a transmitted probe photon are 0.95 and 0.43 respectively.
) and absence of an atom in Rydberg state |r′
, respectively.
state. Vertical and horizontal lines represent threshold counts for state discrimination.
The collectively enhanced optical detection of an atom in |r′ is based on Rydberg EIT in the ladder system |g
↔|e
↔|r
In for the atomic ensemble, which is sensitive to the presence of an individual atom in |r′
. If the state |r′
is not populated, the ensemble exhibits a high transmission T≈0.95 on EIT resonance, while in the presence of an atom in |r′
, the transmission is reduced to T≈0.43: the presence of just one Rydberg atom in |r′
dramatically changes the optical absorption of the entire atomic ensemble (
and |r′
that shifts the state |r
away from EIT resonance. This interaction at distance d is given by Vrr′=C6/d6±C3/d3 with C6/h=6310 GHz·μm6 and C3/h=23.6 GHz·μm3, corresponding to a frequency shift of the EIT transition by Vrr′/h larger than 40 MHz at the rms distance d=d0 between atoms in the ensemble. This shift is comparable to the observed linewidth of ΓEIT/(2π)=26 MHz for a control Rabi frequency Ωc/(2π)=25 MHz. These interactions are not unique to Rb—Rb molecular states. As an example, one could use a Cs133 atom coupled to the Rydberg state|91S> with a Rb87 atom coupled to the Rydberg state |90S>, and thereby one can have interaction strengths of
The value of Ωc is chosen to maximize the signal-to-noise ratio (SNR) by trading off two competing effects: the transmission change depends on the ratio of the blockade radius Rrr′∝Ωc−1/3 to the ensemble size d0, which favors small Ωc. Fast detection, on the other hand, requires large Ωc to increase the group velocity vg∝Ωc2 of the EIT polaritons that are subject to self-blockade in the atomic medium. It will be appreciated that while in this example, transmission of 0.95 and 0.43 are measured, alternative differences in transmission remain suitable for qubit detection as set out herein. For example, a transmission of 0.9 or higher on EIT resonance, with a transmission of 0.5 or lower otherwise, would allow qubit state detection.
In the following, the Rydberg state |r′ is associated with the |↑
state of an effective spin
system. . Even in such a short time, the two distributions 201 and 202 can be clearly distinguished. The time-resolved average count rate (
for |↑
increases with time, whereas the high transmission 204 without an atom in |r′
is almost constant, and decreases only slowly. The linear slope in the time-averaged transmission T|↑
in
during detection, which leads to a sudden increase in transmission at a random time. Such loss is likely due to direct photo-ionization by the control light, and to a lesser part to an auto-ionization process in a collision with one of the slow-light Rydberg polaritons (with a Rydberg component |r
) during detection. The gradual reduction of T without an atom in |r′
may be due to decay of the slow-light |r
-polaritons to other Rydberg states, producing randomly a stationary atom in some Rydberg state, that then blocks the EIT transmission.
A model that includes the random loss of the atom in |r′ yields excellent agreement with the photon count histograms observed at different detection times. Using this model a preparation fidelity may be inferred for the state |↑
(an atom in |r′
) of Fp=0.93±0.02. The detection fidelity (probability of correctly identifying the underlying state IT)) after removing the state preparation error is then Fd=0.92±0.04.
A qubit is implemented in such a system by defining the state with a single atom in |r as the |↓
state. Coherent rotations in the {|↑
, |75
} manifold can be induced by the microwave field. After a qubit rotation, the resulting state is detected by turning on the coupling light slightly (1 μs) earlier than the probe light, such that the state |r
is quickly de-excited by the strong coupling laser to the unstable state |e
, which decays by photon emission in 30 ns (see
(atom in |r′
) is equivalent to having no Rydberg excitation at all, while the state |↑
(atom in |r′
) remains unaffected by the detection light, and leads to Rydberg blockade of the probe transmission. If the photon count is above or below a chosen detection threshold (see
or |↑
, respectively.
population over time, with an associated energy level diagram. A microwave field at a frequency f 0=4814.2 MHz is applied to drive Rabi oscillations between |r′
and |r′
at an oscillation frequency Ω/(2π)=5.3 MHz. Each point is an average of ˜150 repetitions. The error bars are the standard deviation of the mean. The fitted contrast loss per 2π pulse is δC=(1±1)×10−3. The relevant energy level diagrams are shown on the right.
to the magnetic sublevel mj=1/2 in the |91P3/2
manifold, offset by 17 MHz in an applied magnetic field of 10 G. The remaining coupling to other magnetic sublevels limits the maximum Rabi frequency on the |↑
↔|↓
transition to less than ˜5 MHz. The Rabi oscillations show no observable damping on the 6 μs timescale, corresponding to a contrast loss per 2π pulse of δC=(1±1)×10−3.
The observed contrast of the Rabi oscillations can be used to determine the probability that two excitations in |r′ were simultaneously created in the ensemble. Due to the large interaction energy Vrr′(d)=C6/r6±C3/r3 between two atoms in |r′
and |n
, the Rabi oscillations with two excitations would very quickly wash out on a time scale h/Vrr′(d0)˜40 ns. From the observed contrast of the Rabi oscillation it may be concluded that the probability for preparing two excitations is below 1%.
A Ramsey measurement is used to characterize the coherence time of the Rydberg qubit embedded inside the atomic cloud. Two π/2 pulses are applied with a temporal separation T between them, and their relative phase is scanned to obtain a Ramsey fringe at given T.
By harnessing collective effects in a small atomic ensemble, the present disclosure demonstrates methods for the rapid preparation and detection of a Rydberg qubit. The preparation fidelity for a single excitation can be improved by using a smaller ensemble size, since such ensembles would provide even higher energy cost for multiple excitations. The size of the ensemble cannot, however, be made arbitrarily small, since at higher atomic densities, necessary to maintain the same optical depth OD˜1, Rydberg molecule formation could lead to loss. Given atomic densities of n
=2×1011 cm−3, reducing the ensemble size by a factor of 2 should be possible, which would likely reduce the preparation error by more than an order of magnitude. In general, atomic density of less than
n
=1×1013 cm−3 are suitable. Densities higher than this are likely to form Rydberg molecules, which inhibit detection. As used herein, the term optical depth takes its ordinary meaning, the natural logarithm of the ratio of incident to transmitted radiant power through a material. While in some embodiments, an optical depth of about 1 is provided, an optical depth of about 1 to 1.5 is suitable.
Detection fidelity, on the other hand, is limited by the loss of the Rydberg atom prepared in the |r′ state. This loss is mainly caused by the control light in the detection stage, and thus can be mitigated by using two ensembles, one for hosting the qubit and the other for detection, located within a blockade radius from each other. This configuration allows for a non-destructive, fast qubit readout with detection fidelity over 99%, a crucial tool necessary for implementing quantum error correction. In addition, such a readout can also enable studies of quantum feedback, quantum Zeno effect, quantum jumps, and can act as a fast probe of Rydberg super-atom dynamics. The detection scheme can be readily implemented in different Rydberg platforms, and can speed up the optical readout by several orders of magnitude. By scaling up the approach used here to large arrays of small ensembles, the strong Rydberg-Rydberg interactions can be used for multiqubit operations, the study of many-body systems, and in general as a versatile platform for high-fidelity quantum information processing at high speed.
When applied to an ensemble larger than the Rydberg blockade radius, the techniques provided herein permit direct imaging of individual Rydberg atoms inside an ensemble.
87Rb atoms are collected in a three-dimensional magneto-optical trap (MOT) and loaded into a crossed optical dipole trap created with two orthogonal far-detuned laser beams at wavelengths 852 nm (propagating along z) and 1064 nm (propagating along y) with waist sizes w1=10 μm and w2=20 μm, respectively, providing individual trap depths of typically U852/h=2 MHz and U1064/h=20 MHz. The trap vibration frequencies are ωx/(2π)=5.7 kHz, ωy/(2π)=3.0 kHz and ωz(2π)=4.8 kHz. The probe propagates in the xy plane at an angle of 16° to the y axis. The cloud is cooled to 80 μK using polarization gradient cooling, resulting in root-mean-squared (RMS) sizes of x0=2.4 μm, y0=4.6 μm, z0=2.9 μm for the ensemble. The rms distance between two atoms in the ensemble is then d0=√{square root over (2(x02+y02+z02))}=8.4 μm. The total absorption on the |5S1/2, F=2, mF=2→|5P3/2, F=3, mF=3
transition corresponds to N0=440 atoms if the atomic cross section is assumed to be reduced by various broadening mechanisms by a factor of 2 from its maximum value σ0=3λ2/(2π), where λ0=780 nm is the wavelength of the probe transition. A magnetic field of 10 G is applied along the direction of propagation of the probe beam to define the quantization axis and split the magnetic sublevels of the Rydberg states. The optical dipole traps are turned off during state preparation, rotation, and detection to prevent broadening of the transition due to inhomogeneous light shifts of the ground and Rydberg states.
Preparation of an Atom in the Rydberg State
Referring to state vs. microwave frequency relative to fp=4916.1 MHz. Atoms are prepared in the Rydberg state |↑
by means of a three-photon STIRAP-like process.
→|↓
transition during the preparation stage. For small Ωc, the low coupling rate leads to a small population in the Rydberg state. As ΩC increases, the average preparation to |↑
increases as well. Once the whole ensemble is blockaded, photon counts reduce by 34%. To avoid multiple excitations, Ωc=2π×2.4 MHz was chosen, which corresponds to the beginning of the saturated transmission level.
The preparation of the atom in the Rydberg state |↑≡|91P3/2, mj=3/2
is performed with a three-photon STIRAP process as described above. The frequencies of the probe and control laser beams are fixed, and the microwave frequency is scanned to optimize the state initialization stage.
The Rydberg blockade effect is essential for limiting the Rydberg excitation to one atom inside the ensemble. Since the blockade radius is proportional to Ωc−1/3, the probability to have more than one excitation inside the ensemble will increase if the control Rabi frequency Ωc is too high. Ωc is optimized by monitoring the transmission of the probe light during the detection stage (
Loss of the Rydberg Atom and Creation of Rydberg Impurity During Detection
As shown in atom inside the ensemble. Referring to
state, and hence the transmission over time.
For sequences (601) and (602), the photon transmission levels at the time when the probe is turned on are approximately the same. This excludes the possibility that the loss of |r′ is due to the expansion of the gas or to other environment noise during the detection stage. On the other hand, there is a significant difference between the data for sequences (602) and (603). The larger loss for situation (603) indicates that the control light beam induces loss of |r′
, possibly due to direct photoionization into the continuum. However, there is some remaining difference between the transmission for sequences (601) and (602), which suggests some additional loss during detection besides the photoionization effect. The extra loss mechanism may be related to the autoionization process that can occur when the Rydberg polariton with a Rydberg excitation component in |r
collides with the Rydberg atom in |r′
.
The photoionization rate from the control beam is too small. The expected photoionization rate under these conditions is Γpi≈340 s−1, two orders of magnitude smaller that the observed rate constant Γtr≈3.5×104 s−1 for the transmission curve. Furthermore, the repulsive ponderomotive potential of the control beam is too small by three orders of magnitude to explain the increase in transmission with time. On the other hand, a dc electric field of 20-40 mV/cm could provide enough admixture of the 92S Rydberg state to the 91P state so that the state can be coupled with the control laser to 5P3/2, from where it decays to the ground state.
The loss of the Rydberg atom in |r′ during detection is modeled as a sudden change in the transmission. It is assumed that this occurs randomly with constant probability. This model is used to predict the expected histogram of probe photon counts at various detection times and compare it to the experimental data (
The model has four free parameters: the photon rates in the presence and absence of an atom in |r′, respectively, the loss rate for the state |r′
, and the fidelity of initially preparing the atom in |r′
. The experimental data for various detection times are fit, as shown in
A similar model is used to fit the photon histogram for no atom initially prepared in the Rydberg state, where it is assumed that a Rydberg impurity is created at random times by decay of the Rydberg polariton during detection. This process manifests itself as a sudden increase in probe transmission. The histogram and the average transmission are fit to find a Rydberg impurity creation rate of 0.015 μs−1.
The creation of Rydberg impurity, combined with the self-blockade effect, limits the maximum probe photon rate. While a higher photon rate is preferred for faster detection, the fidelity eventually reduces as the probe photon rate increases.
Repeated (Non-Destructive) Detection
Above, a readout fidelity of Fd=0.92±0.04 is provided in a 6 μs readout window, and for 30 counts as a detection threshold. Performing a second measurement in 6 μs with the same threshold shows a detection fidelity in this window of 0.81±0.04 (≈Fd2).
Results for repeated (non-destructive) measurement are given in the table below. |↑ preparation and detection refer to the preparation of an atom in the Rydberg state |91P3/2, mj=1/2
=|r′
. Both the first and second measurements last for 6 μs. The error (standard deviation) for each element in the table is 0.04.
preparation
detection
detection
Measurements of Rabi Oscillations
Magnetic sublevels |r′=|91P3/2, mj=3/2
and |r
=|92S1/2, mj=1/2) are used to define the qubit. However, there is also the possibility of off-resonant coupling to other magnetic sublevels, especially at high Rabi frequency. A magnetic field of 10 G is applied to lift the Zeeman degeneracy, which results in a Zeeman splitting between neighboring magnetic sublevels of ˜17 MHz for the |91P3/2
manifold, and ˜25 MHz for the |92S1/2
manifold. To reduce the coupling to other transitions by the microwave driving fields, two radio frequency antennas are used whose relative amplitude and phase are tuned to suppress the π-polarized transition |92S1/2, mj=1/2
↔|91P3/2, mj=1/2
. A suppression by a factor of 10 is observed compared to a single antenna. A third microwave antenna can be added to also eliminate the σ− transition.
The normalized population of |r′ shown in the Rabi oscillation measurements (
is related to the actual probability p(r′) by the following relation: {tilde over (p)}(r′)=Fp[(1−Fd)+(2Fd−1)p(r′)], which is used to remove the preparation and readout error. Moreover, during the 8-hour measurements of the Rabi oscillations, there were drifts in alignments, which affected the averaged transmitted probe photon number. To account for such long-time drift, two extra reference measurements were added: one without the microwave driving field, and another one without the preparation stage. These two measurements allow monitoring of any slow drift of Fp and Fd, and re-scaling the observed state probabilities.
Rydberg Blockade
Referring to is plotted as a function of separation R at θ=0 calculated from exact diagonalization of the interaction Hamiltonian. The fitted van der Waals interaction coefficient is C6(θ=0)=2π×1.94 THz·μm6, which results in a blockade radius of rB(θ=0)=12 μm.
Preparation Blockade: During the preparation stage, atoms are coupled to the |91P3/2, mJ=3/2 state. A pair of atoms in this state will experience an anisotropic van der Waals interaction Vr′r′=C6(θ)/|R|6, where R is the distance between the pair of atoms and θ is the angle between the pair of atoms and the quantization axis (
Detection Blockade: During the detection stage, the ground state atoms are coupled to the |92S1/2, mJ=1/2 state. Since r and r′ have different parity, they are dominated at large distances by dipole-dipole interactions (˜R−3), while at small distances they are dominated by van der Waals interactions (˜R−6). The dipole-dipole interaction induces the formation of symmetric and anti-symmetric molecular states (|±
=|rr′
±|r′r
/√{square root over (2)}). The blockade radius during the detection stage is defined as V±(rB±)=ℏΓEIT/2, with ΓEIT being the EIT linewidth. The estimated blockade radius for each branch are rB+=12.7 μm and rB−=6.2 μm respectively. The estimated blockaded radius is therefore the average radius from both branches rB=9.4 μm.
pair state interaction energy ΔE vs. separation R at θ=0 calculated from exact diagonalization of the interaction Hamiltonian, illustrating the Rydberg blockade for |rr′
during preparation. The dipole-dipole interaction induces the formation of symmetric (1001) and anti-symmetric (1002) molecular states |±
=(|rr′
±|r′r
)/√{square root over (2)}. Lines correspond to the fitted model A/R6±B/R3, where the fit gives A=C6/h=6310 GHz·μm6 and B=C3/h=23.6 GHz·μm6.
Referring to
In
In
In
In
It will be appreciated that the rectangular configurations of
An aspect of the configurations shown in
Accordingly, in a first example embodiment, the present invention is a device for a fast detection of atoms (or particles) in a Rydberg state. In a 1st aspect of the 1st example embodiment, the device comprises at least one monochromatic light source configured to generate a first optical trap; an ensemble of particles disposed in the first optical trap, each particle of the ensemble of particles being excitable to a first Rydberg state and a second Rydberg state, the second Rydberg state having a blockade radius, each particle of the ensemble of particles being within the blockade radius of each other and within the blockade radius of an atomic qubit, the atomic qubit being a particle that is excitable to the second Rydberg state, the ensemble of particles having a first transmissivity at a first wavelength when neither any particle of the ensemble of particles nor the atomic qubit is in the second Rydberg state, the ensemble of particles having a second transmissivity at the first wavelength when the atomic qubit is in the second Rydberg state, the second transmissivity being lower than the first transmissivity; and a second monochromatic light source configured to drive each particle of the ensemble of particles into the first Rydberg state; a probe light source configured to direct a probe beam having the first wavelength to the ensemble of particles; and a photosensor configured to determine the state of the atomic qubit.
In a 2nd aspect of the 1st example embodiment, the device further comprises a third monochromatic light source configured to drive each particle of the ensemble of particles from a ground state to an intermediate state, and wherein the second monochromatic light source is configured to drive each particle of the ensemble of particles from the intermediate state to the first Rydberg state. The remainder of the features and example features are as described above with respect to the 1st aspect of the 1st example embodiment.
In a 3rd aspect of the 1st example embodiment, the photosensor is configured to measure a transmission of the probe beam by the ensemble of particles. The remainder of the features and example features are as described above with respect to the 1st and 2nd aspects of the 1st example embodiment.
In a 4th aspect of the 1st example embodiment, the photosensor is configured to measure fluorescence of the ensemble of particles at the first wavelength. The remainder of the features and example features are as described above with respect to the 1st through 3rd aspects of the 1st example embodiment.
In a 5th aspect of the 1st example embodiment, the device further comprises a microwave source configured to drive the atomic qubit between the first Rydberg state and the second Rydberg state. The remainder of the features and example features are as described above with respect to the 1st through 4th aspects of the 1st example embodiment.
In a 6th aspect of the 1st example embodiment, the first optical trap is a crossed optical dipole trap. The remainder of the features and example features are as described above with respect to the 1st through 5th aspects of the 1st example embodiment.
In a 7th aspect of the 1st example embodiment, each particle of the ensemble of particles is a 87Rb atom. The remainder of the features and example features are as described above with respect to the 1st through 6th aspects of the 1st example embodiment.
In an 8th aspect of the 1st example embodiment, the first Rydberg state has a blockade radius, and wherein the mean distance between each pair of particles of the ensemble of particles is less than the blockade radius of the first Rydberg state. The remainder of the features and example features are as described above with respect to the 1st through 7th aspects of the 1st example embodiment.
In an 9th aspect of the 1st example embodiment, the ensemble of particles has a total optical depth of about 1. The remainder of the features and example features are as described above with respect to the 1st through 8th aspects of the 1st example embodiment.
In a 10th aspect of the 1st example embodiment, the atomic qubit is disposed in the first optical trap. The remainder of the features and example features are as described above with respect to the 1st through 9th aspects of the 1st example embodiment.
In an 11th aspect of the 1st example embodiment, the device further comprises a plurality of first optical traps forming an array. The remainder of the features and example features are as described above with respect to the 1st through 10th aspects of the 1st example embodiment.
In a 12th aspect of the 1st example embodiment, the array of first optical traps forms a rectangular grid. The remainder of the features and example features are as described above with respect to the 1st through 11th aspects of the 1st example embodiment.
In a 13th aspect of the 1st example embodiment, the atomic qubit is disposed in a second optical trap different from the first optical trap. The remainder of the features and example features are as described above with respect to the 1st through 12th aspects of the 1st example embodiment.
In a 14th aspect of the 1st example embodiment, the device further comprises a plurality of second optical traps forming an array. The remainder of the features and example features are as described above with respect to the 1st through 13th aspects of the 1st example embodiment.
In a 15th aspect of the 1st example embodiment, the array of second optical traps forms a rectangular grid. The remainder of the features and example features are as described above with respect to the 1st through 14th aspects of the 1st example embodiment.
In a 16th aspect of the 1st example embodiment, the second transmissivity is at most 0.5. The remainder of the features and example features are as described above with respect to the 1st aspect through 15th of the 1st example embodiment.
In an 17th aspect of the 1st example embodiment, the first transmissivity is at least 0.9. The remainder of the features and example features are as described above with respect to the 1st aspect through 16th of the 1st example embodiment.
In a 2nd example embodiment, the present invention is a device. In a 1st aspect of the 2nd example embodiment, the device comprises: at least a first monochromatic light source configured to generate a first array of optical traps, each optical trap of the first array of optical traps having an ensemble of particles disposed therein; at least a second monochromatic light source configured to generate a second array of optical traps, wherein: each particle of each of the ensembles of particles being excitable to a first Rydberg state and a second Rydberg state, the second Rydberg state having a blockade radius, each particle of each of the ensembles of particles being within the blockade radius of the second Rydberg state of each particle in its ensemble, and of at least one optical trap of the second array of optical traps, at least one optical trap of the second array having an atomic qubit disposed therein, the atomic qubit being a particle that is excitable to the second Rydberg state, each ensemble of particles having a first transmissivity at a first wavelength when none of its particles is in the second Rydberg state, each ensemble of particles having a second transmissivity at the first wavelength when one particle in the at least one optical trap of the second array of optical traps is in the second Rydberg state, the second transmissivity being lower than the first transmissivity, each particle of each ensemble of particles being outside the blockade radius of the second Rydberg state of each particle of any other ensemble of particles; at least a third monochromatic light source configured to drive each particle of each ensemble of particles into the first Rydberg state; a probe light source configured to direct a probe beam having the first wavelength to the ensembles of particles; and a photosensor configured to determine a quantum mechanical state of at least one particles in the ensembles of particles.
In a 2nd aspect of the 2nd example embodiment, the photosensor is configured to measure a transmission of the probe beam by each of the ensembles of particles. The remainder of the features and example features are as described above with respect to the 1st aspect of the 2nd example embodiment.
In a 3rd aspect of the 2nd example embodiment, the photosensor is configured to measure fluorescence of each of the ensembles of particles at the first wavelength. The remainder of the features and example features are as described above with respect to the 1st through 2nd aspects of the 2nd example embodiment.
In a 4th aspect of the 2nd example embodiment, the first array of optical traps forms a first rectangular grid; and the second array of optical traps forms a second rectangular grid. The remainder of the features and example features are as described above with respect to the 1st through 3rd aspects of the 2nd example embodiment.
In a 5th aspect of the 2nd example embodiment, the first and second rectangular grids are congruent to each other, and exactly one optical trap of the second array of optical traps is within the blockade radius of the second Rydberg state of the particles of each ensemble of particles. The remainder of the features and example features are as described above with respect to the 1st through 4th aspects of the 2nd example embodiment.
In a 6th aspect of the 2nd example embodiment, the first and second rectangular grids are configured so that exactly two optical traps of the second array of optical traps are within the blockade radius of the second Rydberg state of the particles of each ensemble of particles. The remainder of the features and example features are as described above with respect to the 1st through 5th aspects of the 2nd example embodiment.
In a 7th aspect of the 2nd example embodiment, the first and second rectangular grids are configured so that exactly four optical traps of the second array of optical traps are within the blockade radius of the second Rydberg state of the particles of each ensemble of particles. The remainder of the features and example features are as described above with respect to the 1st through 6th aspects of the 2nd example embodiment.
In a 3rd example embodiment, the present invention is a method of determining a state of an atomic qubit. In a 1st aspect of the 3rd example embodiment, the method comprises: disposing an ensemble of particles proximate to an atomic qubit, wherein: each particle of the ensemble of particles being excitable to a first Rydberg state and a second Rydberg state, the second Rydberg state having a second blockade radius, the atomic qubit being a particle that is excitable to the second Rydberg state, each particle of the ensemble of particles being within the second Rydberg state blockade radius of each other and within the second Rydberg state blockade radius of the atomic qubit, the ensemble of particles having a first transmissivity at a first wavelength when neither any particle of the ensemble of particles nor the atomic qubit is in the second Rydberg state, the ensemble of particles having a second transmissivity at the first wavelength when the atomic qubit is in the second Rydberg state, the second transmissivity being lower than the first transmissivity; driving any one particle of the ensemble of particles into the first Rydberg state; directing a probe beam having the first wavelength to the ensemble of particles; and determining the state of the atomic qubit.
In a 2nd aspect of the 3rd example embodiment, determining the state of the atomic qubit comprises measuring a transmission of the probe beam by the ensemble of particles. The remainder of the features and example features are as described above with respect to the 1st aspect of the 3rd example embodiment.
In a 3rd aspect of the 3rd example embodiment, determining the state of the atomic qubit comprises measuring fluorescence of the ensemble of particles at the first wavelength. The remainder of the features and example features are as described above with respect to the 1st through 2nd aspects of the 3rd example embodiment.
In a 4th aspect of the 3rd example embodiment, the method further comprises performing a computation using the atomic qubit prior to driving any one particle of the ensemble of particles into the first Rydberg state. The remainder of the features and example features are as described above with respect to the 1st through 3rd aspects of the 3rd example embodiment.
In a 5th aspect of the 3rd example embodiment, the method further comprises moving the atomic qubit, thereby disposing the atomic qubit proximal to the ensemble of particles.
The present disclosure may be embodied as a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.
The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.
Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.
Computer readable program instructions for carrying out operations of the present disclosure may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure.
Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.
These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.
The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.
The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.
The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
This application is a continuation of International Application No. PCT/US2022/016173, filed Feb. 22, 2022, which claims the benefit of U.S. Provisional Application No. 63/148,995, filed Feb. 12, 2021, each of which is hereby incorporated by reference in its entirety.
This invention was made with government support under W911NF2010021 and D18AC00037 awarded by the Department of Defense/Defense Advanced Research Projects Agency; U.S. Pat. Nos. 1,125,846 and 1,506,284 awarded by the National Science Foundation; and W911NF1520067 awarded by the U.S. Army Research Laboratory. The Government has certain rights in the invention.
Number | Date | Country | |
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63148995 | Feb 2021 | US |
Number | Date | Country | |
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Parent | PCT/US2022/016173 | Feb 2022 | US |
Child | 18233088 | US |