Patent Description:
<NPL> describes the phenomenon of electromagnetically induced transparency (EIT) of cold atomic gas (a "cloud" of Rb atoms). It describes that when the atoms in the cloud are placed in Rydberg states, the transmissivity of the cloud is affected. It further demonstrates that subjecting the entire cloud to microwave irradiation (microwave dressing) enhances the Rydberg blockade-dependent transmissivity of the cloud.

<NPL>), describes optical traps and their uses in implementing neutral atom qubits.

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.

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 <NUM> µs with a success probability of Fp = <NUM> ± <NUM>. The qubit is manipulated, and its state is read out in <NUM> µs with a single-shot fidelity of Fd = <NUM> ± <NUM>. The ensemble-assisted collective optical readout speeds up state detection by a factor of <NUM><NUM> compared to imaging of a single atom. Qubit coherence times of <NUM> µs are observed, much longer than the π rotation time of <NUM> 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 <NUM> 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 ~ <NUM>) process that has only moderate fidelity, and the state-dependent removal of atoms followed by relatively slow (τ ~ <NUM>) fluorescence imaging of the remaining atoms with fidelities of F ≳ <NUM>. While fast high-intensity fluorescence readout within <NUM> 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 ~ <NUM> trapped ultracold <NUM>Rb atoms, a qubit is prepared between the Rydberg states |r'〉 = |<NUM>P<NUM>/<NUM>, mj = <NUM>/<NUM>〉 and |r〉 ≡ |<NUM>S<NUM>/<NUM>, mj = <NUM>/<NUM>〉. Qubit rotations are performed with a loss of contrast δC ≤ <NUM> × <NUM>-<NUM> 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 = <NUM>µs and Td = <NUM>µs with fidelities of Fp = <NUM> ± <NUM> and Fd = <NUM> ± <NUM>, respectively. The measured qubit coherence time of τc = (<NUM> ± <NUM>) µs is much longer than the π rotation time of <NUM> 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, <NPL>)). 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 <FIG>, a fast collective detector of a single Rydberg atom is illustrated. <FIG> is a schematic view of a state initialization. An atom is prepared in the Rydberg state |r'〉 through a three-photon process involving the preparation beam (Ωp, <NUM>), the control beam (Ωc, <NUM>), and a microwave field (ΩMW, <NUM>). The detunings from the two intermediate states are Δe = δr = 2π × <NUM>. 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 = <NUM>S〉 and |r' = <NUM>S〉, which have the energy difference of ΔE = <NUM> GHz.

<FIG> is a schematic view of an ensemble of atoms <NUM> and its transmissivity. A probe field (<NUM>, waist size wp = <NUM>) in combination with the control field (<NUM>, waist size wc = <NUM>) couples atoms to the first Rydberg state |r〉. The waist size of the control beam <NUM> is configured to uniformly illuminate the ensemble <NUM>. The waist size of the probe beam <NUM> is configured to be smaller than and ideally centered on the ensemble <NUM>. Under conditions of electromagnetically induced transparency (EIT) (Δe = δr = <NUM>), 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 <NUM> (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 <FIG>, a small ensemble with root-mean-square (rms) size of <MAT> containing typically N ~ <NUM> laser-cooled <NUM>Rb atoms is prepared inside a two-beam optical dipole trap with waist sizes w<NUM> = <NUM>µm and w<NUM> = <NUM>µm. The atoms are optically pumped into the hyperfine and magnetic sublevel |g〉 = |<NUM>S<NUM>/<NUM>, F = <NUM>, mF = <NUM>) that is coupled via a two-photon process involving the transitions |g〉 ↔ |e〉 ≡ |<NUM>P<NUM>/<NUM>, F = <NUM>, mF = <NUM>) (preparation beam Ωp) and |e〉 ↔ |r〉 (control beam Ωc) to the Rydberg state |r〉 = |<NUM>S<NUM>/<NUM>, mj = <NUM>/<NUM>〉 When the two-photon transition is resonant with the intermediate state (Δe = <NUM>, see <FIG>), the transmitted probe light serves for Rydberg state detection under conditions of electromagnetically induced transparency (EIT). As described above, and shown in <FIG> (left detail), if neither any particle of the ensemble <NUM> nor the atomic qubit <NUM> is in the second Rydberg state |r'〉, then the ensemble <NUM> exhibits a high (first) transmissivity of the probe beam <NUM> on EIT resonance, while, as shown in <FIG> (right detail), when the atomic qubit <NUM> is in the second Rydberg state |r'〉, then the ensemble <NUM> has a low (second) transmissivity of the probe beam <NUM>, lower than the first transmissivity. A photosensor <NUM> determines the state of the atomic qubit <NUM>. In one embodiment, as shown in <FIG>, the photosensor <NUM> is configured to measure the transmission of the probe beam <NUM>.

In another embodiment, as shown in <FIG>, the photosensor <NUM> is configured to measure fluorescence of the ensemble of particles <NUM> at the probe (first) wavelength <NUM>. For detection of fluorescent light, the collection of light is done by imaging the ensemble of particles <NUM> with a high-numerical aperture lens (NA ><NUM>) such as a microscope objective <NUM> onto a EMCCD camera <NUM>. The collected fluorescence serves as the amplified signal, since the amount of light scattered is proportional to the number of atoms in the ensemble. All detection statistics described before apply with this method.

To prepare a single atom in the Rydberg state |r'〉 ≡ |<NUM>P<NUM>/<NUM>, mj = <NUM>/<NUM>〉 inside the ensemble, the probe laser and microwave field are detuned by Δe/(2π) = δr/(2π) = <NUM> from their respective transitions, and in combination with the control field drive a three-photon transition |g〉 ↔ |e〉 ↔ |r〉 ↔ |r'〉 (see <FIG>). By changing the powers of the two optical fields within ~<NUM>µs, a process similar to stimulated Raman adiabatic passage (STIRAP) is realized. This process is chosen over direct excitation because it is less sensitive to laser noise and atom number fluctuations. The observed linewidth Γ<NUM>/(<NUM>π) = <NUM> of the three-photon transition corresponds to a blockade radius of Rr'r' ~ <NUM> µm for the preparation process, larger than the rms distance d<NUM> ≡
<MAT> 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 <FIG>, a histogram is provided of the transmitted probe photon number for state detection performed in <NUM>. Histograms <NUM> and <NUM> correspond to the presence (state |↑〉) and absence of an atom in Rydberg state |r'〉, respectively. The solid lines in <FIG>indicate a theoretical model that for the presence (absence) of an atom in |r'〉 assumes random sudden ionization of the Rydberg atom in |r'〉 (sudden decay of the slow-light polariton into a Rydberg state) at a rate <NUM>-<NUM> (<NUM>-<NUM>). The dashed line indicates the detection threshold that equalizes the errors for misidentifying the underlying two states. The control Rabi frequency is Ωc/(2π) = <NUM>, and the probabilities for collecting and detecting a transmitted probe photon are <NUM> and <NUM> respectively. <FIG> is a graph of time-resolved photon count rate during detection, where <NUM> and <NUM> correspond to the presence (state |↑〉) and absence of an atom in Rydberg state |r'〉, respectively. <FIG> is a correlation plot of number of detected-photon counts in two consecutive <NUM>µs measurements in the same run of the experiment. Gray points concentrated in the lower left (upper right) quadrant represent transmission data when preparing (not preparing) the |↑〉 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〉 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 ≈ <NUM> on EIT resonance, while in the presence of an atom in |r'〉, the transmission is reduced to T ≈ <NUM>: the presence of just one Rydberg atom in |r'〉 dramatically changes the optical absorption of the entire atomic ensemble (<FIG> and <FIG>). The transmission change is a consequence of the strong interaction between atoms in the highly excited Rydberg states |r〉 and |r'〉 that shifts the state |r〉 away from EIT resonance. This interaction at distance d is given by Vrr' = C<NUM>/d<NUM> ± C<NUM>/d<NUM> with C<NUM>/h = <NUM>· µm<NUM> and C<NUM>/h = <NUM>· µm<NUM>, corresponding to a frequency shift of the EIT transition by Vrr,/h larger than <NUM> at the rms distance d = d<NUM> between atoms in the ensemble. This shift is comparable to the observed linewidth of ΓEIT/(<NUM>π) = <NUM> for a control Rabi frequency Ωc/(<NUM>π) = <NUM>. These interactions are not unique to Rb-Rb molecular states. As an example, one could use a Cs133 atom coupled to the Rydberg state | <NUM> > with a Rb87 atom coupled to the Rydberg state <NUM>>, and thereby one can have interaction strengths of <MAT> µm<NUM> and <MAT>. 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 <MAT> to the ensemble size d<NUM>, which favors small Ωc. Fast detection, on the other hand, requires large Ωc to increase the group velocity <MAT> 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 <NUM> and <NUM> are measured, alternative differences in transmission remain suitable for qubit detection as set out herein. For example, a transmission of <NUM> or higher on EIT resonance, with a transmission of <NUM> or lower otherwise, would allow qubit state detection.

In the following, the Rydberg state |r'〉 is associated with the |↑〉 state of an effective spin <MAT> system. <FIG> shows the observed photon count histograms of the transmitted light in a <NUM>-µs detection window with (<NUM>) and without (<NUM>) an atom in |r'〉. Even in such a short time, the two distributions <NUM> and <NUM> can be clearly distinguished. The time-resolved average count rate (<FIG>) reveals that the transmission <NUM> T|↑〉 for |↑〉 increases with time, whereas the high transmission <NUM> without an atom in |r'〉 is almost constant, and decreases only slowly. The linear slope in the time-averaged transmission T|↑〉 in <FIG> can be explained by a light-induced loss process of the Rydberg atom 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 = <NUM> ± <NUM>. The detection fidelity (probability of correctly identifying the underlying state |↑〉) after removing the state preparation error is then Fd = <NUM> ± <NUM>.

<FIG> demonstrates that repeated ('non-destructive') measurements can be performed on the system, where a second <NUM>µs measurement yields good agreement with the first measurement: The average conditional probability for the second measurement to have the same outcome as the first measurement is p = <NUM> ± <NUM>. The detection system can also be viewed as a single-atom transistor for light. A gain of G = <NUM> ± <NUM> is achieved in <NUM>µs.

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 {|↑〉, |↓〉} manifold can be induced by the microwave field. After a qubit rotation, the resulting state is detected by turning on the coupling light slightly (<NUM> 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 <NUM> ns (see <FIG>). Thus, as far as the detection process is concerned, the state |↓〉 (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 <FIG>), the qubit state is identified as |↓〉 or |↑〉, respectively.

<FIG> is a set of graphs of |r'〉 population over time, with an associated energy level diagram. A microwave field at a frequency f<NUM> = <NUM> is applied to drive Rabi oscillations between |r〉 and |r'〉 at an oscillation frequency Ω/(2π) = <NUM>. Each point is an average of ~ <NUM> repetitions. The error bars are the standard deviation of the mean. The fitted contrast loss per 2π pulse is δC = (<NUM> ± <NUM>) × <NUM>-<NUM>. The relevant energy level diagrams are shown on the right.

<FIG> shows Rabi oscillations with the full sequence of state preparation, qubit rotation, and detection. Since the trapping light creates a repulsive potential for the Rydberg states, the trap is turned off during the entire sequence, which puts a constraint on the operation time. This limitation could be alleviated in the future by the use of recently developed techniques of optical trapping using ponderomotive forces. Two microwave antennas are used with adjusted relative phase and amplitude to suppress the π polarization component of the microwave field that can couple atoms on |↓〉 to the magnetic sublevel mj = <NUM>/<NUM> in the |<NUM>P<NUM>/<NUM>〉 manifold, offset by <NUM> in an applied magnetic field of <NUM>. The remaining coupling to other magnetic sublevels limits the maximum Rabi frequency on the |↑〉 ↔ |↓〉 transition to less than ~ <NUM>. The Rabi oscillations show no observable damping on the <NUM> µs timescale, corresponding to a contrast loss per <NUM>π pulse of δC = (<NUM> ± <NUM>) × <NUM>-<NUM>.

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) = C<NUM>/r<NUM> ± C<NUM>/r<NUM> between two atoms in |r'〉 and |r〉, the Rabi oscillations with two excitations would very quickly wash out on a time scale h/Vrr'(d<NUM>) ~ <NUM> ns. From the observed contrast of the Rabi oscillation it may be concluded that the probability for preparing two excitations is below <NUM>%.

A Ramsey measurement is used to characterize the coherence time of the Rydberg qubit embedded inside the atomic cloud. Two π/<NUM> pulses are applied with a temporal separation T between them, and their relative phase is scanned to obtain a Ramsey fringe at given T. <FIG> displays the contrast of the Ramsey fringes as a function of Ramsey time T. By fitting the contrast to a Gaussian decay function, the e-<NUM> dephasing time is given as (<NUM> ± <NUM>) µs. Possible dephasing mechanisms include electric-field fluctuations acting on the highly polarizable Rydberg states, magnetic field fluctuations, and interactions between the Rydberg atom and the surrounding ground state atoms.

<FIG> is a graph of contrast over time, showing Ramsey measurements consisting of two π/<NUM> pulses separated by a time τ. The phase of the second π/<NUM> pulse is scanned to obtain a Ramsey fringe. The contrast of the Ramsey fringe is plotted as a function of τ. The solid curve is a fit to a Gaussian decay function Ae-(τ/T*)<NUM>, yielding a dephasing time
<MAT> and A = <NUM> ± <NUM>. The inset shows the Ramsey fringe at τ = <NUM> ns.

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 ~ <NUM>, Rydberg molecule formation could lead to loss. Given atomic densities of 〈n〉 = <NUM> × <NUM><NUM> cm-<NUM>, reducing the ensemble size by a factor of <NUM> 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〉 = <NUM> × <NUM><NUM> cm-<NUM> 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 <NUM> is provided, an optical depth of about <NUM> to <NUM> 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 <NUM>%, 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.

<NUM>Rb 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 <NUM> (propagating along z) and <NUM> (propagating along y) with waist sizes w<NUM> = <NUM>µm and w<NUM> = <NUM>µm, respectively, providing individual trap depths of typically U<NUM>/h = <NUM> and U<NUM>/h = <NUM>. The trap vibration frequencies are ωx/(<NUM>π) = <NUM>, ωy/(<NUM>π) = <NUM> and ωz(<NUM>π) = <NUM>. The probe propagates in the xy plane at an angle of <NUM>° to the y axis. The cloud is cooled to <NUM> µK using polarization gradient cooling, resulting in root-mean-squared (RMS) sizes of x<NUM> = <NUM> µm, y<NUM> = <NUM> µm, z<NUM> = <NUM> µm for the ensemble. The rms distance between two atoms in the ensemble is then <MAT>. The total absorption on the |<NUM>S<NUM>/<NUM>, F = <NUM>, mF = <NUM>〉 → |<NUM>P<NUM>/<NUM>, F = <NUM>, mF = <NUM>) transition corresponds to N<NUM> = <NUM> atoms if the atomic cross section is assumed to be reduced by various broadening mechanisms by a factor of <NUM> from its maximum value σ<NUM> = <NUM>λ<NUM>/(<NUM>π), where λ<NUM> = <NUM> is the wavelength of the probe transition. A magnetic field of <NUM> 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.

Referring to <FIG>, optimization of Rydberg preparation is illustrated. <FIG> shows the spectrum of the <NUM>-photon resonance absorption to the |↑〉 state vs. microwave frequency relative to fp = <NUM>. Atoms are prepared in the Rydberg state |↑〉 by means of a three-photon STIRAP-like process. <FIG> shows photon counts integrated over a <NUM> window in the detection stage as a function of ΩC, the coupling of the |e〉 → |↓〉 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 <NUM>%. To avoid multiple excitations, Ωc = 2π × <NUM> was chosen, which corresponds to the beginning of the saturated transmission level.

The preparation of the atom in the Rydberg state |↑〉 ≡|<NUM>P<NUM>/<NUM>, mj = <NUM>/<NUM>〉 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. <FIG> displays the transmission of probe light during the detection stage as a function of the microwave frequency used for state preparation. fp = <NUM> was chosen, which maximizes the preparation probability.

The Rydberg blockade effect is essential for limiting the Rydberg excitation to one atom inside the ensemble. Since the blockade radius is proportional to <MAT>, 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 (<FIG>), and choosing the value Ωc = 2π × <NUM> that corresponds to the onset of saturation.

As shown in <FIG>, the rising slope of the transmitted photon count <NUM> during detection suggests a non-zero loss rate for the |r'〉 atom inside the ensemble. Referring to <FIG>, to obtain insight into the loss mechanism, three different experimental sequences are compared: keeping both the probe and control light beams on for ~ <NUM>µs (curve <NUM>); turning on the control light <NUM>µs earlier than the probe light (curve <NUM>); and turning both control and probe light on at the same time, but <NUM>µs later than case <NUM> (curve <NUM>). Points on curve <NUM> represent the data where both control and probe light are turned on for <NUM>, points on curve <NUM> represent the data when control light was on for the entire <NUM> and probe light is turned on only for the last <NUM>. Points on curve <NUM> represent the data when both control and probe light are turned on only for the last <NUM>. From the photon rate level of each sequence, one can conclude that control light has the most effect in increasing the loss of the |r'〉 state, and hence the transmission over time.

For sequences (<NUM>) and (<NUM>), 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 (<NUM>) and (<NUM>). The larger loss for situation (<NUM>) 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 (<NUM>) and (<NUM>), 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 ≈ <NUM>s-<NUM>, two orders of magnitude smaller that the observed rate constant Γtr ≈ <NUM> × <NUM><NUM>s-<NUM> 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 <NUM>-<NUM> mV/cm could provide enough admixture of the <NUM> Rydberg state to the 91P state so that the state can be coupled with the control laser to <NUM>P<NUM>/<NUM> , 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 (<FIG>).

<FIG>are histograms showing measured distributions at varying start times of probing window with an integration time of <NUM>. These distributions are fit using the theoretical model to obtain the loss rate and preparation fidelity. The inferred preparation fidelity is Fp = <NUM> ± <NUM>.

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 <FIG>, and a loss rate of <NUM> µs-<NUM> and a preparation fidelity of Fp = <NUM> ± <NUM> are found. The model also captures the average rise in transmission <NUM> that is observed, as shown in <FIG>.

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 <NUM> µs-<NUM>.

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. <FIG> plots the detection fidelity at various photon rates. A photon rate of <NUM>/µs was chosen for the measurements shown above.

<FIG> plots the fidelity of detection as a function of the detected probe photon count rate in the absence of atomic ensemble with optimized readout time for each data point (between <NUM> and <NUM>). The data have been corrected for the preparation fidelity.

Above, a readout fidelity of Fd = <NUM> ± <NUM> is provided in a <NUM>µs readout window, and for <NUM> counts as a detection threshold. Performing a second measurement in <NUM>µs with the same threshold shows a detection fidelity in this window of <NUM> ± <NUM> (≈ <MAT>). <FIG> shows the correlations between the two measurements; the results are summarized in the table below. This correlation between consecutive measurements is a signature of quantum non-demolition measurements (QND), and under ideal conditions the measurement would not be expected to induce any change in the state. The average conditional probability that the second measurement yields the same result as the first measurement is <NUM> ± <NUM>.

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 |<NUM>P<NUM>/<NUM>, mj = <NUM>/<NUM>〉 = |r'〉. Both the first and second measurements last for <NUM>µs. The error (standard deviation) for each element in the table is <NUM>.

Magnetic sublevels |r'〉 = |<NUM>P<NUM>/<NUM>, mJ = <NUM>/<NUM>〉 and |r〉 = |<NUM>S<NUM>/<NUM>, mJ = <NUM>/<NUM>〉 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 <NUM> is applied to lift the Zeeman degeneracy, which results in a Zeeman splitting between neighboring magnetic sublevels of ~ <NUM> for the |<NUM>P<NUM>/<NUM>〉 manifold, and ~ <NUM> for the |<NUM>S<NUM>/<NUM>〉 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 |<NUM>S<NUM>/<NUM>, mJ = <NUM>/<NUM>〉 ↔ |<NUM>P<NUM>/<NUM>, mJ = <NUM>/<NUM>〉. A suppression by a factor of <NUM> 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 (<FIG>) are corrected by the preparation infidelity (<NUM> - Fp) and the detection infidelity (<NUM> - Fd). The measured probability p̃(r') of detecting |r'〉 is related to the actual probability p(r') by the following relation: p̃(r') = Fp[(<NUM> - Fd) + (<NUM>Fd - <NUM>)p(r')], which is used to remove the preparation and readout error. Moreover, during the <NUM>-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.

Referring to <FIG>, Rydberg blockade during preparation is illustrated. In <FIG>, the interaction energy ΔE between two atoms in state |r'〉 is plotted as a function of separation R at θ = <NUM> calculated from exact diagonalization of the interaction Hamiltonian. The fitted van der Waals interaction coefficient is C<NUM>(θ = <NUM>) = 2π × <NUM> THz · µm<NUM>, which results in a blockade radius of rB(θ = <NUM>) = <NUM>. <FIG> is a plot of rB(θ) vs. θ. Due to the anisotropy of the atomic wave-functions involved, the resulting interaction resembles an ellipsoid with aspect ratio of <NUM>, with the semi-major axis at <NUM>° from the quantization axis. This curve was obtained by perturbatively calculating C<NUM>(θ).

Preparation Blockade: During the preparation stage, atoms are coupled to the |<NUM>P<NUM>/<NUM>, mJ = <NUM>/<NUM>〉 state. A pair of atoms in this state will experience an anisotropic van der Waals interaction Vr'r' = C<NUM>(θ)/|R|<NUM>, where R is the distance between the pair of atoms and θ is the angle between the pair of atoms and the quantization axis (<FIG>). From this interaction the effective blockade radius can be estimated as Vr'r'(rB(θ)) = ℏΓ<NUM>/<NUM> where Γ<NUM> is the full width half maximum of the <NUM>-photon resonance, Γ<NUM> = <NUM>π × <NUM>. A blockade radius of about <NUM> µm along the quantization direction (θ = <NUM>) is estimated. The resulting blockade volume has an ellipsoid shape with an aspect ratio of <NUM>, as shown on <FIG>. The average blockade radius of the ellipsoid is rB = <NUM> µm.

Detection Blockade: During the detection stage, the ground state atoms are coupled to the |<NUM>S<NUM>/<NUM>, mJ = <NUM>/<NUM>) state. Since r and r' have different parity, they are dominated at large distances by dipole-dipole interactions (~ R-<NUM>), while at small distances they are dominated by van der Waals interactions (~ R-<NUM>). The dipole-dipole interaction induces the formation of symmetric and anti-symmetric molecular states <MAT>. The blockade radius during the detection stage is defined as V±(rB±) = ℏΓEIT/<NUM>, with ΓEIT being the EIT linewidth. The estimated blockade radius for each branch are rB+ = <NUM> µm and rB- = <NUM> µm respectively. The estimated blockaded radius is therefore the average radius from both branches rB = <NUM> µm.

<FIG> plots the |rr'〉 pair state interaction energy ΔE vs. separation R at θ = <NUM> 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 (<NUM>) and anti-symmetric (<NUM>) molecular states |±〉 = <MAT>. Lines correspond to the fitted model A/R<NUM> ± B/R<NUM>, where the fit gives A = C<NUM>/h = <NUM> · µm<NUM> and B = C<NUM>/h = <NUM> · µm<NUM>.

Referring to <FIG>, various exemplary geometries are illustrated enabling readout of a plurality of qubits.

In <FIG>, an array of optical traps, each indicated by a large circle in solid line, are arranged in a rectangular grid. Each optical trap <NUM> includes an ensemble of atoms as described above. In addition, each optical trap <NUM> includes an atomic qubit <NUM>, each indicated by a small circle in solid line. The blockade radius <NUM> of the particles of each ensemble, indicated by a dashed circle, encompasses each optical trap and the qubit therein.

In <FIG>, an array of optical traps, each indicated by a large circle in solid line, are arranged in a rectangular grid. Each optical trap <NUM> includes an ensemble of atoms as described above. A second array of optical traps is provided, each optical trap of the second array includes an atomic qubit <NUM>, each indicated by a small circle in solid line. The blockade radius <NUM> of the particles of each ensemble, indicated by a dashed circle, encompasses each optical trap and exactly one adjacent qubit. It will be appreciated that in this example, two arrays of optical traps are congruent with each other.

In <FIG>, an array of optical traps, each indicated by a large circle in solid line, are arranged in a rectangular grid. Each optical trap <NUM> includes an ensemble of atoms as described above. A second array of optical traps is provided, each optical trap of the second array includes an atomic qubit <NUM>, each indicated by a small circle in solid line. The blockade radius <NUM> of the particles of each ensemble, indicated by a dashed circle, encompasses each optical trap and exactly four adjacent qubits. It will be appreciated that in this example, the two arrays of optical traps are of different sizes, the optical traps holding the qubits being spaced more closely than the optical traps holding the ensembles.

In <FIG>, an array of optical traps, each indicated by a large circle in solid line, are arranged in a rectangular grid. Each optical trap <NUM> includes an ensemble of atoms as described above. A second array of optical traps is provided, each optical trap of the second array includes an atomic qubit <NUM>, each indicated by a small circle in solid line. The blockade radius <NUM> of the particles of each ensemble, indicated by a dashed circle, encompasses each optical trap and exactly two adjacent qubits. It will be appreciated that in this example, the two arrays of optical traps are of different sizes, the optical traps holding the qubits being spaced more closely than the optical traps holding the ensembles.

It will be appreciated that the rectangular configurations of <FIG> are presented by way of example and not limitation. A variety of physical configurations may be employed to read out single qubits or groups of qubits.

An aspect of the configurations shown in <FIG> taking <FIG> as an example, is that every atom <NUM> in the single atom array needs to be within the blockade radius <NUM> of an ensemble <NUM> for detection. Given recent experimental developments, it is possible to move atoms within the single atom array. This modified configuration, shown in <FIG>, includes a detection region <NUM> where an array of ensembles of atoms <NUM> exists separate from the single atom array region <NUM> (computation region). In the computational region <NUM>, atoms <NUM> can be entangled into a collective state by means of a two-photon entanglement gate by pulse shaping the Rydberg and probing lasers' intensity, frequency and phase to optimize for state preparation. To detect the entangled state, individual atoms <NUM> are moved by generating traps with an acousto-optic deflector which enables generation of multiple diffraction orders by using multiple tones to control the trap positions in real time. This capability enables moving atoms <NUM> from the computational region <NUM> to the detection region <NUM> such that a moved atom <NUM> is within the blockade radius <NUM> of any of the ensembles <NUM>. After the move, light shines into the ensemble <NUM> and the transmission of the ensemble <NUM> is detected as described above. After detection, the individual atoms can be moved back to the computation region <NUM>.

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 <NUM>st aspect of the <NUM>st 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 <NUM>nd aspect of the <NUM>st 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 <NUM>st aspect of the <NUM>st example embodiment.

In a <NUM>rd aspect of the <NUM>st 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 <NUM>st and <NUM>nd aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>rd aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st example embodiment, each particle of the ensemble of particles is a <NUM>Rb atom. The remainder of the features and example features are as described above with respect to the <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In an <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In an <NUM>th aspect of the <NUM>st example embodiment, the ensemble of particles has a total optical depth of about <NUM>. The remainder of the features and example features are as described above with respect to the <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In an <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st 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 <NUM>st through <NUM>th aspects of the <NUM>st example embodiment.

In a <NUM>th aspect of the <NUM>st example embodiment, the second transmissivity is at most <NUM>. The remainder of the features and example features are as described above with respect to the <NUM>st aspect through <NUM>th of the <NUM>st example embodiment.

In an <NUM>th aspect of the <NUM>st example embodiment, the first transmissivity is at least <NUM>. The remainder of the features and example features are as described above with respect to the <NUM>st aspect through <NUM>th of the <NUM>st example embodiment.

In a <NUM>nd example embodiment, the present invention is a device. In a <NUM>st aspect of the <NUM>nd 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 <NUM>nd aspect of the <NUM>nd 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 <NUM>st aspect of the <NUM>nd example embodiment.

In a <NUM>rd aspect of the <NUM>nd 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 <NUM>st through <NUM>nd aspects of the <NUM>nd example embodiment.

In a <NUM>th aspect of the <NUM>nd 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 <NUM>st through <NUM>rd aspects of the <NUM>nd example embodiment.

In a <NUM>th aspect of the <NUM>nd 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 <NUM>st through <NUM>th aspects of the <NUM>nd example embodiment.

In a <NUM>th aspect of the <NUM>nd 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 <NUM>st through <NUM>th aspects of the <NUM>nd example embodiment.

In a <NUM>th aspect of the <NUM>nd 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 <NUM>st through <NUM>th aspects of the <NUM>nd example embodiment.

In a <NUM>rd example embodiment, the present invention is a method of determining a state of an atomic qubit. In a <NUM>st aspect of the <NUM>rd 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 <NUM>nd aspect of the <NUM>rd 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 <NUM>st aspect of the <NUM>rd example embodiment.

In a <NUM>rd aspect of the <NUM>rd 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 <NUM>st through <NUM>nd aspects of the <NUM>rd example embodiment.

In a <NUM>th aspect of the <NUM>rd 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 <NUM>st through <NUM>rd aspects of the <NUM>rd example embodiment.

In a <NUM>th aspect of the <NUM>rd 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.

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. 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.

Claim 1:
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.