Real-time adaptive qubit readout via time-dependent photon detection count thresholds

Abstract

A result of a qubit reading operation is determined by obtaining a photon detection count for a time step of the qubit reading operation performed on a qubit; based at least in part on the photon detection count for the time step, determining whether a bright threshold criteria is satisfied and / or determining whether a dark threshold criteria is satisfied. Responsive to determining that the bright threshold criteria is satisfied, and indication that the qubit is in a bright state is stored. Responsive to determining that the dark threshold criteria is satisfied, an indication that the qubit is in a dark state is stored. Responsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, it is determined that a state of the qubit is undetermined.

Description

REAL-TIME ADAPTIVE QUBIT READOUT VIATIME-DEPENDENT PHOTON DETECTION COUNT THRESHOLDSCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Application No. 19 / 075,201, filed March 10, 2025, and U.S. Application No. 63 / 637,157, filed April 22, 2024, the contents of which are incorporated herein by reference in their entireties.TECHNICAL FIELD

[0002] Various embodiments relate to apparatuses, systems, and methods relating to determining a quantum state of a qubit. For example, various embodiments relate to the use of time-dependent threshold criteria for determining the quantum state of a qubit. For example, some example embodiments relate to a reading procedure for reading the state of a qubit of a quantum charge-coupled device (QCCD)-based quantum computer.BACKGROUND

[0003] Conventional qubit reading operations for atomic qubit-based quantum computers include applying a laser beam to the qubit to be read. When the qubit is in a “bright” qubit state, the laser beam being incident on the qubit causes the qubit to fluoresce. When the qubit is in a “dark” qubit state, the laser beam being incident on the qubit does not cause the qubit to fluoresce. By counting the number of photons detected over a set length of time and comparing that number to a set threshold value, a determination of whether the qubit is in the bright qubit state or the dark qubit state is made. The set length of time needs to be long enough for the determination to be made with a selected accuracy (e.g., a selected confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). However, the longer the laser beam is on (e.g., the longer the set length of time), the more opportunity there is for the laser beam to cause cross-talk errors or for state mixing to result in a detection error (e.g., determining an incorrect qubit state for the qubit). Through applied effort, ingenuity, and innovation many deficiencies of prior qubit state determination techniques have been solved by developing solutions that are structured in accordance with the embodiments of the present invention, many examples of which are described in detail herein.BRIEF SUMMARY OF EXAMPLE EMBODIMENTS

[0004] Example embodiments provide methods, systems, apparatuses, computer program products and / or the like for performing qubit state determination of qubits using timedependent threshold criteria. For example, various embodiments provide methods, systems, apparatuses, computer program products, and / or the like for performing qubit reading operations where, at a plurality of time steps, a photon detection count indicating the number of photons detected during a respective time step is used to determine whether a bright threshold criteria corresponding to the respective time step is satisfied, whether a dark threshold criteria corresponding to the time step is satisfied, or whether neither the bright threshold criteria nor the dark threshold criteria corresponding to the respective time step is satisfied. In various embodiments, satisfaction of the bright threshold criteria causes determination that the qubit is in the bright qubit state and satisfaction of the dark threshold criteria causes determination that the qubit is in the dark qubit state. In various embodiments, once the qubit state of the qubit is determined, the qubit reading operation may be halted, even if the qubit reading operation has not been performed for the set length of time. Thus, the probability of cross-talk errors or detection errors are reduced.

[0005] According to an aspect of the present disclosure, a method for determining a result of a qubit reading operation is provided. In an example embodiment, the method is performed by a processing device of a controller, for example. In an example embodiment, the method includes obtaining, by the processing device, a photon detection count for a time step of the qubit reading operation performed on a qubit; based at least in part on the photon detection count for the time step, determining, by the processing device, at least one of whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied; responsive to determining that the bright threshold criteria is satisfied, determining, by the processing device, that the qubit is in a bright state; responsive to determining that the dark threshold criteria is satisfied, determining, by the processing device, that the qubit is in a dark state; and responsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, determining, by the processing device, that a state of the qubit is undetermined.

[0006] In an example embodiment, the time step is one of a plurality of time steps.

[0007] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied includes determining a representative photon detection count based at least in part on the photon detection count for the time step; and comparing the representative photon detection count toat least one of a bright state threshold corresponding to the time step or a dark state threshold corresponding to the time step.

[0008] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied further includes responsive to determining that the representative photon detection count is greater than the bright state threshold corresponding to the time step, determining that the qubit is in the bright state; responsive to determining that the representative photon detection count is less than or equal to the dark state threshold corresponding to the time step, determining that the qubit is in the dark state; and responsive to determining that the representative photon detection count is less than or equal to the bright state threshold corresponding to the time step and greater than the dark state threshold corresponding to the time step, determining that the state of the qubit is undetermined.

[0009] In an example embodiment, the method further includes responsive to determining that the qubit is in the dark state or to determining that the qubit is in the bright state, causing the qubit reading operation to stop being performed.

[0010] In an example embodiment, the method further includes, responsive to determining that the state of the qubit is undetermined, causing the qubit reading operation to continue being performed.

[0011] In an example embodiment, the method further includes responsive to determining that the state of the qubit is undetermined, determining whether an amount of time for which the qubit reading operation has been performed has reached a maximum reading operation duration; and responsive to determining that the amount of time for which the qubit reading operation has been performed has reached the maximum reading operation duration, causing the performance of the qubit reading operation to stop.

[0012] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored in a non-transitory memory accessible to the processing device.

[0013] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored as one or more look up tables and the processing device comprises a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) configured to determine at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied.

[0014] In an example embodiment, the bright threshold criteria and the dark threshold criteria are defined based at least in part on one or more simulations of a qubit reading operation and a selected accuracy.

[0015] In an example embodiment, the selected accuracy is a function of a reading operation duration such that at a maximum reading operation duration a bright state threshold of the bright threshold criteria is equal to a dark state threshold of the dark threshold criteria.

[0016] In an example embodiment, the method further includes accessing a bright state threshold corresponding to the time step and accessing a dark state threshold corresponding to the time step, wherein the bright state threshold corresponding to the time step is used to determine whether the bright threshold criteria are satisfied and the dark state threshold corresponding to the time step is used to determine whether the dark threshold criteria are satisfied.

[0017] According to another aspect, a controller configured to determine a result of a qubit reading operation is provided. In an example embodiment, the controller includes a processing device and a memory and the controller is configured to perform obtaining, by the processing device, a photon detection count for a time step of the qubit reading operation performed on a qubit; based at least in part on the photon detection count for the time step, determining, by the processing device, at least one of whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied; responsive to determining that the bright threshold criteria is satisfied, determining, by the processing device, that the qubit is in a bright state; responsive to determining that the dark threshold criteria is satisfied, determining, by the processing device, that the qubit is in a dark state; and responsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, determining, by the processing device, that a state of the qubit is undetermined.

[0018] In an example embodiment, the time step is one of a plurality of time steps.

[0019] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied includes determining a representative photon detection count based at least in part on the photon detection count for the time step; and comparing the representative photon detection count to at least one of a bright state threshold corresponding to the time step or a dark state threshold corresponding to the time step.

[0020] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied further includes responsive to determining that the representative photon detection count is greater than the bright state threshold corresponding to the time step, determining that the qubit is in the bright state; responsive to determining that the representative photon detection count is less than or equal to the dark state threshold corresponding to the time step, determining that thequbit is in the dark state; and responsive to determining that the representative photon detection count is less than or equal to the bright state threshold corresponding to the time step and greater than the dark state threshold corresponding to the time step, determining that the state of the qubit is undetermined.

[0021] In an example embodiment, the controller is further configured to perform, responsive to determining that the qubit is in the dark state or to determining that the qubit is in the bright state, causing the qubit reading operation to stop being performed.

[0022] In an example embodiment, the controller is further configured to perform, responsive to determining that the state of the qubit is undetermined, causing the qubit reading operation to continue being performed.

[0023] In an example embodiment, the controller is further configured to perform, responsive to determining that the state of the qubit is undetermined, determining whether an amount of time for which the qubit reading operation has been performed has reached a maximum reading operation duration; and responsive to determining that the amount of time for which the qubit reading operation has been performed has reached the maximum reading operation duration, causing the performance of the qubit reading operation to stop.

[0024] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored in a non-transitory memory accessible to the processing device.

[0025] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored as one or more look up tables and the processing device comprises a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) configured to determine at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied.

[0026] In an example embodiment, the bright threshold criteria and the dark threshold criteria are defined based at least in part on one or more simulations of a qubit reading operation and a selected accuracy.

[0027] In an example embodiment, the selected accuracy is a function of a reading operation duration such that at a maximum reading operation duration a bright state threshold of the bright threshold criteria is equal to a dark state threshold of the dark threshold criteria.

[0028] In an example embodiment, the controller is further configured to perform accessing a bright state threshold corresponding to the time step and accessing a dark state threshold corresponding to the time step, wherein the bright state threshold corresponding to the time step is used to determine whether the bright threshold criteria are satisfied and thedark state threshold corresponding to the time step is used to determine whether the dark threshold criteria are satisfied.

[0029] According to another aspect, a system is provided. In an example embodiment, the system includes a confinement apparatus configured to confine a plurality of quantum objects; a manipulation source configured to generate and provide at least one manipulation signal; an optics collection system comprising at least one photodetector configured to detect photons fluoresced by a qubit of the plurality of quantum objects, wherein the optics collection system is configured to generate a sensor signal corresponding to detection of photons by the photodetector and the sensor signal to a controller; and the controller configured to control operation of the confinement apparatus and the manipulation source and to receive one or more sensor signals generated by the optics collection system. In an example embodiment, the controller is configured to perform obtaining, by the processing device, a photon detection count for a time step of the qubit reading operation performed on a qubit; based at least in part on the photon detection count for the time step, determining, by the processing device, at least one of whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied; responsive to determining that the bright threshold criteria is satisfied, determining, by the processing device, that the qubit is in a bright state; responsive to determining that the dark threshold criteria is satisfied, determining, by the processing device, that the qubit is in a dark state; and responsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, determining, by the processing device, that a state of the qubit is undetermined.

[0030] In an example embodiment, the time step is one of a plurality of time steps.

[0031] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied includes determining a representative photon detection count based at least in part on the photon detection count for the time step; and comparing the representative photon detection count to at least one of a bright state threshold corresponding to the time step or a dark state threshold corresponding to the time step.

[0032] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied further includes responsive to determining that the representative photon detection count is greater than the bright state threshold corresponding to the time step, determining that the qubit is in the bright state; responsive to determining that the representative photon detection count is less than or equal to the dark state threshold corresponding to the time step, determining that thequbit is in the dark state; and responsive to determining that the representative photon detection count is less than or equal to the bright state threshold corresponding to the time step and greater than the dark state threshold corresponding to the time step, determining that the state of the qubit is undetermined.

[0033] In an example embodiment, the controller is further configured to perform, responsive to determining that the qubit is in the dark state or to determining that the qubit is in the bright state, causing the qubit reading operation to stop being performed.

[0034] In an example embodiment, the controller is further configured to perform, responsive to determining that the state of the qubit is undetermined, causing the qubit reading operation to continue being performed.

[0035] In an example embodiment, the controller is further configured to perform, responsive to determining that the state of the qubit is undetermined, determining whether an amount of time for which the qubit reading operation has been performed has reached a maximum reading operation duration; and responsive to determining that the amount of time for which the qubit reading operation has been performed has reached the maximum reading operation duration, causing the performance of the qubit reading operation to stop.

[0036] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored in a non-transitory memory accessible to the processing device.

[0037] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored as one or more look up tables and the processing device comprises a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) configured to determine at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied.

[0038] In an example embodiment, the bright threshold criteria and the dark threshold criteria are defined based at least in part on one or more simulations of a qubit reading operation and a selected accuracy.

[0039] In an example embodiment, the selected accuracy is a function of a reading operation duration such that at a maximum reading operation duration a bright state threshold of the bright threshold criteria is equal to a dark state threshold of the dark threshold criteria.

[0040] In an example embodiment, the controller is further configured to perform accessing a bright state threshold corresponding to the time step and accessing a dark state threshold corresponding to the time step, wherein the bright state threshold corresponding to the time step is used to determine whether the bright threshold criteria are satisfied and thedark state threshold corresponding to the time step is used to determine whether the dark threshold criteria are satisfied.

[0041] In an example embodiment, the controller is further configured to control operation of the manipulation source to cause the manipulation source to generate a reading manipulation signal and provide the reading manipulation signal such that the reading manipulation signal is incident on the qubit.

[0042] In an example embodiment, the controller is further configured to determine the photon detection count for the time step based at least in part on the one or more sensor signals.

[0043] According to another aspect, a computer program product is provided. In an example embodiment, the computer program product comprises at least one non-transitory computer-readable medium storing executable instructions. The executable instructions are configured to, when executed by a processing device of a controller, causes the controller to perform obtaining, by the processing device, a photon detection count for a time step of the qubit reading operation performed on a qubit; based at least in part on the photon detection count for the time step, determining, by the processing device, at least one of whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied; responsive to determining that the bright threshold criteria is satisfied, determining, by the processing device, that the qubit is in a bright state; responsive to determining that the dark threshold criteria is satisfied, determining, by the processing device, that the qubit is in a dark state; and responsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, determining, by the processing device, that a state of the qubit is undetermined.

[0044] In an example embodiment, the time step is one of a plurality of time steps.

[0045] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied includes determining a representative photon detection count based at least in part on the photon detection count for the time step; and comparing the representative photon detection count to at least one of a bright state threshold corresponding to the time step or a dark state threshold corresponding to the time step.

[0046] In an example embodiment, determining at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied further includes responsive to determining that the representative photon detection count is greater than the bright state threshold corresponding to the time step, determining that the qubit is in thebright state; responsive to determining that the representative photon detection count is less than or equal to the dark state threshold corresponding to the time step, determining that the qubit is in the dark state; and responsive to determining that the representative photon detection count is less than or equal to the bright state threshold corresponding to the time step and greater than the dark state threshold corresponding to the time step, determining that the state of the qubit is undetermined.

[0047] In an example embodiment, the executable instructions are further configured to, when executed by a processing device of a controller, causes the controller to perform, responsive to determining that the qubit is in the dark state or to determining that the qubit is in the bright state, causing the qubit reading operation to stop being performed.

[0048] In an example embodiment, the executable instructions are further configured to, when executed by a processing device of a controller, causes the controller to perform, responsive to determining that the state of the qubit is undetermined, causing the qubit reading operation to continue being performed.

[0049] In an example embodiment, the executable instructions are further configured to, when executed by a processing device of a controller, causes the controller to perform, responsive to determining that the state of the qubit is undetermined, determining whether an amount of time for which the qubit reading operation has been performed has reached a maximum reading operation duration; and responsive to determining that the amount of time for which the qubit reading operation has been performed has reached the maximum reading operation duration, causing the performance of the qubit reading operation to stop.

[0050] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored in a non-transitory memory accessible to the processing device.

[0051] In an example embodiment, the bright threshold criteria and the dark threshold criteria are stored as one or more look up tables.

[0052] In an example embodiment, the bright threshold criteria and the dark threshold criteria are defined based at least in part on one or more simulations of a qubit reading operation and a selected accuracy.

[0053] In an example embodiment, the selected accuracy is a function of a reading operation duration such that at a maximum reading operation duration a bright state threshold of the bright threshold criteria is equal to a dark state threshold of the dark threshold criteria.

[0054] In an example embodiment, the executable instructions are further configured to, when executed by a processing device of a controller, causes the controller to perform accessing a bright state threshold corresponding to the time step and accessing a dark statethreshold corresponding to the time step, wherein the bright state threshold corresponding to the time step is used to determine whether the bright threshold criteria are satisfied and the dark state threshold corresponding to the time step is used to determine whether the dark threshold criteria are satisfied.

[0055] In an example embodiment, the controller is further configured to control operation of the manipulation source to cause the manipulation source to generate a reading manipulation signal and provide the reading manipulation signal such that the reading manipulation signal is incident on the qubit.

[0056] In an example embodiment, the controller is further configured to determine the photon detection count for the time step based at least in part on the one or more sensor signals.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0057] Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0058] Figure 1 is a schematic diagram illustrating an example quantum computing system configured for performing a qubit reading operation of an example embodiment.

[0059] Figure 2 is a schematic diagram of some of the energy levels of an example quantum object that may be used in performing a qubit reading operation of an example embodiment.

[0060] Figure 3 is a flowchart illustrating various processes, operations, and / or procedures of generating and / or determining bright threshold criteria and dark threshold criteria, in accordance with an example embodiment.

[0061] Figure 4A provides a plot illustrating example bright threshold criteria and example dark threshold criteria, in accordance with an example embodiment.

[0062] Figure 4B provides a plot illustrating example bright threshold criteria and example dark threshold criteria, in accordance with another example embodiment.

[0063] Figure 5 is a flowchart illustrating various processes, operations, and / or procedures of performing a qubit reading operation and / or determining a qubit state of a qubit, in accordance with an example embodiment.

[0064] Figure 6 provides a schematic diagram of an example controller of a quantum computer configured to perform one or more deterministic reshaping and / or reordering functions, according to various embodiments.

[0065] Figure 7 provides a schematic diagram of an example computing entity of a quantum computer system that may be used in accordance with an example embodiment.DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

[0066] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. The term “or” (also denoted “ / ”) is used herein in both the alternative and conjunctive sense, unless otherwise indicated. The terms “illustrative” and “exemplary” are used to be examples with no indication of quality level. The terms “generally,” “substantially,” and “approximately” refer to within engineering and / or manufacturing tolerances and / or within user measurement capabilities, unless otherwise indicated. Like numbers refer to like elements throughout.

[0067] Example embodiments provide methods, systems, apparatuses, computer program products and / or the like for performing qubit state determination of qubits using timedependent threshold criteria. For example, various embodiments provide methods, systems, apparatuses, computer program products, and / or the like for performing qubit reading operations where, at a plurality of time steps, a photon detection count indicating the number of photons detected during a respective time step is used to determine whether a bright threshold criteria corresponding to the respective time step is satisfied, whether a dark threshold criteria corresponding to the time step is satisfied, or whether neither the bright threshold criteria nor the dark threshold criteria corresponding to the respective time step is satisfied. In various embodiments, satisfaction of the bright threshold criteria causes determination that the qubit is in the bright qubit state and satisfaction of the dark threshold criteria causes determination that the qubit is in the dark qubit state. In various embodiments, once the qubit state of the qubit is determined, the qubit reading operation may be halted, even if the qubit reading operation has not been performed for the set length of time. Thus, the probability of cross-talk errors or detection errors are reduced.

[0068] For example, a model of a qubit may be generated and used to determine and / or generate bright threshold criteria and dark threshold criteria. For example, the model of the qubit may be arbitrarily complex and may include a bright qubit state scattering rate, dark qubit state scattering rate, background scattering rate, state mixing rates, and / or other processes that may affect the fluorescence of a qubit being read. Selected accuracies (e.g., aconfidence level threshold, likelihood ratio threshold, or Bayesian likelihood ratio threshold) may be selected for each time step, and based thereon and the model of the qubit, bright state thresholds corresponding to a plurality of time steps of a qubit reading operation are determined and dark state thresholds corresponding to the plurality of time steps of a qubit reading operation are determined. The bright state thresholds and the dark state thresholds corresponding to the plurality of time steps may then be stored for use during in determining a qubit state of qubit during performance of a qubit reading operation on the qubit.

[0069] In various embodiments, the bright state threshold and / or the dark state threshold are time-dependent. For example, the bright state threshold and / or the dark state threshold corresponding to an ith time step of the plurality of time steps may be different from (e.g., not equal to) a respective one of the bright state threshold and / or the dark sate threshold for a jth time step of the plurality of time steps, for i j . In an example embodiment, the bright state threshold and / or dark state threshold are representative count thresholds. For example, the bright state threshold and / or the dark state threshold may be cumulative photon detection count thresholds, average photon detection count thresholds, individual time step or a sliding window sum of photon detection counts, and / or the like. In an example embodiment, a cumulative photon detection count for the ith time step Ni is the sum of the photon detection counts nk detected during each time step through the ith time step (N^ = k=onk)- Inanexample embodiment, the average photon detection count for the ith time step ntis the average photon count detection of the photon detection count nk during each time step through the ith time step (nt= fc=onk / (i + 1))-

[0070] During operation of a quantum computer (e.g., to perform a quantum circuit and / or program), a qubit reading operation may be performed on a qubit. For example, a reading manipulation signal may be caused to be incident on the qubit to determine whether or not the qubit fluoresces in response to the reading manipulation signal being incident thereon. During an ith time step of the qubit reading operation, an ith photon detection count ni corresponding to the qubit is detected by an optics collection system of the quantum computer. Based at least in part on the ith photon detection count ni, it is determined whether the bright threshold criteria or the dark threshold criteria corresponding to the ith time step is satisfied.

[0071] For example, the cumulative photon detection count Nt= fc=onk is determined based at least in part on the ith photon detection count ni. The cumulative photon detection count Ni may then be compared to a bright state threshold of the bright threshold criteriacorresponding to the ith time step. When the cumulative photon detection count Ni is greater than the bright state threshold corresponding to the ith time step, it is determined that the qubit is in the bright state. The cumulative photon detection count Ni may be compared to a dark state threshold of the dark threshold criteria corresponding to the ith time step. When the cumulative photon detection count Ni is less than or equal to the dark state threshold corresponding to the ith time step, it is determined that the qubit is in the dark state. When the cumulative photon detection count Ni is less than or equal to the bright state threshold corresponding to the ith time step and greater than the dark state threshold corresponding to the ith time step, it is determined that the state of the qubit is ambiguous.

[0072] In various embodiments, when the state of the qubit is determined to be the bright state or the dark state, the qubit reading operation may be concluded (e.g., the reading manipulation signal may stop being provided and / or applied to the qubit) even if the qubit reading operation has been performed for less than the set length of time. When the state of the qubit is determined to be ambiguous, the qubit reading operation may be continued.

[0073] During performance of the qubit reading operation, at each time step, the bright state threshold and the dark state threshold corresponding to the time step may be accessed from (local) memory (e.g., via a look-up table or other datastore) and a representative photon detection count (e.g., cumulative photon detection count, average photon detection count, individual time step photon detection count, a sliding window sum of photon detection counts, and / or the like) corresponding to the time step is compared to the bright state threshold and / or the dark state threshold corresponding to the time step. Based on the results of comparing the representative photon detection count corresponding to the time step to the bright state threshold and / or the dark state threshold corresponding to the time step, a determination of whether the state of the qubit is the bright state, the dark state, or ambiguous is made. Therefore, the computations performed in real-time during the performance of the qubit reading operation are able to be performed quickly and / or with minimal computational resources.

[0074] Conventional qubit reading operations for atomic qubit-based quantum computers include applying a laser beam to the qubit to be read. When the qubit is in a “bright” qubit state, the laser beam being incident on the qubit causes the qubit to fluoresce. When the qubit is in a “dark” qubit state, the laser beam being incident on the qubit does not cause the qubit to fluoresce. By counting the number of photons detected over a set length of time and comparing that number to a set threshold value, a determination of whether the qubit is in the bright qubit state or the dark qubit state is made. The set length of time needs to be longenough for the determination to be made with a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). However, the longer the laser beam is on (e.g., the longer the set length of time), the more opportunity there is for the laser beam to cause cross-talk errors or for state mixing to result in a detection error (e.g., determining an incorrect qubit state for the qubit).

[0075] Previous attempts to enable shorter qubit reading operation performance times (e.g., adaptive detection methods) tend to be too computationally costly to perform in realtime and / or use approximations to enable real-time use but that sacrifice the precision of the detection. Therefore, technical problems exist regarding how to reduce the amount of time that the qubit reading operation is performed without sacrificing the precision and / or the confidence level with which the qubit state is determined.

[0076] Various embodiments provide technical solutions to these technical problems. For example, in various embodiments, the time-dependent bright threshold requirement and timedependent dark threshold requirement are pre-determined to provide qubit state determination with a desired level of accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). Thus, the precision of qubit state determinations in accordance with various embodiments satisfy the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) requirements of the particular application.Moreover, for each time step, a bright state threshold and a dark state threshold corresponding to the threshold are read and the representative photon detection count corresponding to the time step is compared to one or both of the bright state threshold and the dark state threshold corresponding to the time step. Therefore, minimal computational resources are required to perform the adaptive detection in real-time during performance of the qubit reading operation.

[0077] As a result of being able to perform the adaptive detection in real-time during performance of the qubit reading operation, it is possible to determine the state of the qubit with a desired level of a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) after a time period of performing the qubit reading operation that is less than the set length of time, in various instances. Once the state of the qubit is determined with the desired level of a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), performance of the qubit reading operation may be stopped, halted, or concluded even if the qubit reading operation has not yet been performed for the set length of time. This results in the reading manipulation signal being provided and / or applied to the qubit for a shorter amount of time than the set length of time,in various instance. As such, cross-talk errors and detection errors (e.g., due to state mixing, etc.) are reduced.

[0078] Thus, various embodiments provide technical improvements to the fields of quantum computing, qubit reading operations, quantum state determination, and similar fields.Example Quantum Computing System

[0079] One example type of system in which it may be desired to determine a quantum state of a quantum particle is a quantum computer. For example, the quantum state of a qubit of the quantum computer may be determined to determine the result of a quantum computation.

[0080] Figure 1 provides a schematic diagram of an example quantum computing system 100 comprising a confinement apparatus 70 configured to confine quantum objects used as the qubits of the quantum computer, in accordance with an example embodiment. For example, the quantum computing system 100 may be a QCCD-based quantum computing system. For example, the confinement apparatus 70 may be an ion trap and the quantum objects may be ions. In another example, the confinement apparatus 70 may be an optical trap or magnetic-optical trap and the quantum objects may be neutral atoms. Various confinement apparatuses 70 and corresponding quantum objects may be used in various embodiments, as appropriate for the application.

[0081] In various embodiments, the quantum computing system 100 comprises a computing entity 10 and a quantum computer 110. In various embodiments, the quantum computer 110 comprises a controller 30, a cryostat and / or vacuum chamber 40 enclosing a confinement apparatus 70, and one or more manipulation sources 60. For example, the cryostat and / or vacuum chamber 40 may be a pressure-controlled chamber. In an example embodiment, the one or more manipulation sources 60 may comprise one or more lasers (e.g., optical lasers, microwave sources, and / or the like). In various embodiments, the one or more manipulation sources 60 are configured to manipulate and / or cause a controlled quantum state evolution of one or more quantum objects confined by the confinement apparatus. For example, the manipulation sources 60 may be configured to generate a reading manipulation signal configured for performing a qubit reading operation on one or more qubits confined by the confinement apparatus 70. For example, in an example embodiment, wherein the one or more manipulation sources 60 comprise one or more lasers, the lasers may provide one or more manipulation signals in the form of laser beams to quantum objects confined by theconfinement apparatus 70 within the cryostat and / or vacuum chamber 40. In various embodiments, the manipulation signals may be continuous or pulsed laser beams.

[0082] In various embodiments, the quantum computer 110 comprises an optics collection system 80 configured to collect and / or detect photons generated, emitted, and / or fluoresced by qubits (e.g., during qubit reading operations). The optics collection system 80 may comprise one or more optical elements (e.g., lenses, mirrors, waveguides, fiber optics cables, and / or the like) and one or more photodetectors. In various embodiments, the photodetectors may be photodiodes, photomultipliers, charge-coupled device (CCD) sensors, complementary metal oxide semiconductor (CMOS) sensors, Micro-Electro-Mechanical Systems (MEMS) sensors, and / or other photodetectors that are sensitive to light at an expected fluorescence wavelength of the qubits of the quantum computer. In various embodiments, the detectors may be in electronic communication with the controller 30 via one or more A / D converters 625 (see Figure 6) and / or the like.

[0083] In various embodiments, the quantum computer 110 comprises one or more voltage sources 50. For example, the voltage sources 50 may comprise a plurality of voltage drivers and / or voltage sources and / or at least one RF driver and / or voltage source. The voltage sources 50 may be electrically coupled to the corresponding potential generating elements (e.g., electrodes) of the confinement apparatus 70, in an example embodiment.

[0084] In various embodiments, a computing entity 10 is configured to allow a user to provide input to the quantum computer 110 (e.g., via a user interface of the computing entity 10) and receive, view, and / or the like output from the quantum computer 110. The computing entity 10 may be in communication with the controller 30 of the quantum computer 110 via one or more wired or wireless networks 20 and / or via direct wired and / or wireless communications. In an example embodiment, the computing entity 10 may translate, configure, format, and / or the like information / data, quantum computing algorithms and / or circuits, and / or the like into a computing language, executable instructions, command sets, and / or the like that the controller 30 can understand and / or implement.

[0085] In various embodiments, the controller 30 is configured to control the voltage sources 50, cryostat system and / or vacuum system controlling the temperature and pressure within the cryostat and / or vacuum chamber 40, manipulation sources 60, and / or other systems controlling various environmental conditions (e.g., temperature, pressure, and / or the like) within the cryostat and / or vacuum chamber 40 and / or configured to manipulate and / or cause a controlled evolution of quantum states of one or more quantum objects within the confinement apparatus. For example, the controller 30 may cause a controlled evolution ofquantum states of one or more quantum objects within the confinement apparatus to execute a quantum circuit and / or algorithm. For example, the controller 30 may cause a qubit reading operation to be performed that uses time-dependent photon count detection thresholds, such as the time-dependent bright state threshold and the time-dependent dark state threshold, on a qubit confined by the confinement apparatus 70. In various embodiments, the quantum objects confined within the confinement apparatus are used as qubits of the quantum computer 110.Example Qubit Reading Operation

[0086] In various embodiments, a qubit reading operation is performed by applying a reading manipulation signal to a qubit (e.g., causing the reading manipulation signal to be incident on the qubit) and determining the qubits response to the reading manipulation signal being incident thereon.

[0087] Figure 2 illustrates a portion of an energy space 200 for an example quantum object that may be used as a qubit of the quantum computing system, in an example embodiment. For example, a qubit sub-space 210 of the energy space 200 of the quantum object may be defined. In various embodiments, the qubit sub-space 210 is defined to include a first qubit state 212 and a second qubit state 214. For example, the qubit sub-space 210 may comprise a first qubit state 212 of the 1 = 0, m = 0 hyperfine state of the ground state (e.g., the S1 / 2manifold) of the quantum object, which may be referred to as the zero or off state (e.g., 10)) or the down state (e.g., |4)), in various embodiments. The qubit sub-space 210 may further comprise a second qubit state 214 of the 1 = 1, m = 0 hyperfine state of the ground state of the quantum object, which may be referred to as the one or on state (e.g., 11) or the up state (e.g., |T)), in various embodiments. In the illustrated embodiment, the first qubit state 212 is the dark qubit state and the second qubit state 214 is the bright qubit state. In other embodiments, the first qubit state 212 may be the bright state and the second qubit state 214 may be the dark state.

[0088] In various embodiments, the quantum object is an ion or atom. For example, the quantum object may be singly ionized ytterbium, singly ionized barium, and / or the like. The quantum object being used as a qubit of the quantum system is also referred to herein simply as a qubit.

[0089] In various embodiments, the two states of the qubit sub-space 210 may be separated by a qubit state separation frequency fq. In various embodiments, the qubit stateseparation frequency fqis a frequency in the range of 2 to 20 GHz. In various embodiments, the dark qubit state is first mapped to a long-lived auxiliary state that is dark to the reading manipulation signal. For example, the dark qubit state may be shelved to a long-lived auxiliary state during performance of and / or as part of performing the reading operation. In various embodiments, the long-lived auxiliary state is in the D5 / 2 or F7 / 2 excited state manifolds of trapped ions.

[0090] In various embodiments, the energy space 200 of the quantum object also includes an excited state 220. In various embodiments, the excited state 220 is a state in a P-manifold or D-manifold of the quantum object. To perform a qubit reading operation, a reading manipulation signal 230 is caused to be incident on and / or applied to the qubit (e.g., the quantum object being used as the qubit). The reading manipulation signal 230 is characterized by a reading frequency frthat corresponds to a frequency difference between the bright qubit state (e.g., the second qubit state 214 in the illustrated embodiment) and the excited state 220. For example, the reading manipulation signal 230 is configured to drive a transition from the bright qubit state (e.g., the second qubit state 214 in the illustrated embodiment) to the excited state 220. For example, the reading frequency fris resonant with the transition between the bright qubit state (e.g., the second qubit state 214 in the illustrated embodiment) and the excited state 220. In various embodiments, the excited state 220 is a short-lived state such that the qubit decays from the excited state 220 via a decay transition 232. As part of the decay transition 232, the qubit emits photons 234. The photons 234 are detected via photodetectors of the optics collection system 80.

[0091] The reading manipulation signal 230 does not drive a transition between the dark qubit state (e.g., the first qubit state 212 in the illustrated embodiment) and the excited state 220. For example, the reading frequency fris off-resonant for the transition between the dark qubit state (e.g., the first qubit state 212 in the illustrated embodiment) and the excited state 220. Thus, application of the reading manipulation signal 230 does not cause the qubit to emit photons 234.

[0092] Due to the quantum (e.g., probabilistic) nature of the decay of the quantum object, the quantum object may decay from the excited state 220 to a state of the energy space 200 that is not the bright state and possibly not within the qubit sub-space. For example, the energy space 200 may include other states having energies that are less than the excited state 220 that are not shown in Figure 2. In such embodiments, performing the qubit reading operation may further include applying one or more optical repump manipulation signals to the quantum object such that if the quantum object decays from the excited state 220 to astate of the energy space 200 other than the bright qubit state (e.g., the second qubit state 214 in the illustrated embodiment) the qubit may be repumped such that the quantum object may decay back to the bright qubit state.

[0093] Notably, the quantum (e.g., probabilistic) nature of the quantum object and the interactions therewith result in state mixing and / or the like that may result in, even when the qubit is in the dark state (e.g., the first qubit state 212 in the illustrated embodiment), the photodetectors of the optics collection system 80 may detect photons during the qubit reading operation. Therefore, determination of the state of a qubit is not as simple as determining whether the optics collection system 80 detected photons corresponding to the qubit reading operation of the qubit or not.

[0094] Figure 3 provides a flowchart illustrating various processes, procedures, operations, and / or the like for generating and providing bright threshold requirements and dark threshold requirements for use during a qubit reading operation.

[0095] Starting at step 302, the quantum object and interactions of the quantum object with the reading manipulation signal 230 and any optical repump manipulation signals is modeled. For example, the modeling of the quantum object and interactions of the quantum object with the reading manipulation signal 230 and any optical repump manipulation signals is used to determine bright threshold criteria and dark threshold criteria. In various embodiments, the modeling of the quantum object and interactions of the quantum object with the reading manipulation signal 230 and any optical repump manipulation signals is performed by a classical (e.g., semiconductor-based) computing entity 10 and / or the controller 30. For example, the computing entity 10 and / or controller may comprise means, such as processing device 605, 708 (see Figures 6 and 7), memory 610, 722, 724, and / or the like, for modeling the quantum object and interactions of the quantum object with the reading manipulation signal 230 and any optical repump manipulation signals and determining bright threshold criteria and dark threshold criteria based at least in part thereon.

[0096] In various embodiments, a model of the quantum object is used to determine bright state thresholds and dark state thresholds corresponding to a plurality of time steps. For example, the model may use and / or receive as input a bright qubit state scattering rate, a dark qubit state scattering rate, a background scattering rate, state mixing rates, and / or other information corresponding to the energy space 200 and / or transitions between various states of the energy space 200. In various embodiments, the model may use and / or receive as input information corresponding to the reading manipulation signal and any optical repump manipulation signals. The model is configured to simulate interaction of the quantum objectwith the reading manipulation signal (and possibly with one or more optical repump signals generated and / or provided by one or more manipulation sources 60) to determine photon time of arrival information for scenarios where the quantum object is in the dark qubit state (e.g., the first qubit state 212 in the embodiment illustrated in Figure 2) and for scenarios where the quantum object is in the bright qubit state (e.g., the second qubit state 214 in the embodiment illustrated in Figure 2).

[0097] Based at least in part on the photon time of arrival information for scenarios where the quantum object is in the dark qubit state and for scenarios where the quantum object is in the bright qubit state, bright state thresholds for a plurality of time steps are determined and dark state thresholds for a plurality of time steps are determined. For example, a bright state threshold for a time step delineates between representative photon detection counts (e.g., cumulative photon detection count, average photon detection count, individual time step photon detection count, a sliding window sum of photon detection counts, and / or the like) for the time step that, with a particular and / or selected level of a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), indicate that the qubit is in the bight qubit state from representative photon detection counts for the time step do not indicate that the qubit is in the bright qubit state with the particular and / or selected level of a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). In another example, a dark state threshold for a time step delineates between representative photon detection counts (e.g., cumulative photon detection count, average photon detection count, individual time step photon detection count, a sliding window sum of photon detection counts, and / or the like) for the time step that, with a particular and / or selected level of a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), indicate that the qubit is in the dark qubit state from representative photon detection counts for the time step do not indicate that the qubit is in the dark qubit state with the particular and / or selected level of a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like).

[0098] For example, the photon time of arrival information (and possibly photon capture efficiency information for the optics collection system 80, and / or the like) may be used to determine, for a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), a maximum representative photon detection count for each time step of the plurality of time steps of the qubit reading operation when the qubit is in the dark qubit state. For example, when for a respective time step of a qubit reading operation the representative photon detection count for the respective time step is less than (or less than orequal to) the maximum representative photon detection count for the respective time step, it may be determined with a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), that the qubit is in the dark qubit state. The maximum representative photon detection count for the respective time step may be selected as the dark state threshold for the respective time step. For example, the dark state threshold for the respective time step may be determined based on the maximum representative photon detection count for the respective time step.

[0099] For example, the photon time of arrival information (and possibly photon capture efficiency information for the optics collection system 80, and / or the like) may be used to determine, for a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), a minimum representative photon detection count for each time step of the plurality of time steps of the qubit reading operation when the qubit is in the bright qubit state. For example, when for a respective time step of a qubit reading operation the representative photon detection count for the respective time step is greater than or equal to (or greater than) the minimum representative photon detection count for the respective time step, it may be determined with the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like), that the qubit is in the bright qubit state. The minimum representative photon detection count for the respective time step may be selected as the bright state threshold for the respective time step. For example, the bright state threshold for the respective time step may be determined based on the minimum representative photon detection count for the respective time step.

[0100] Figure 4A provides a plot 400A that illustrates example bright state thresholds 402 for a plurality of time steps (to - tio) and example dark state thresholds 404 for the plurality of time steps. The bright state thresholds 402 and the dark state thresholds 404 separate the representative photon detection counts space into a bright detection region 410, an ambiguous detection region 420, and a dark detection region 430. When the representative photon detection count for a time step is in the bright detection region 410, it may be determined with the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) that the qubit being read is in the bright qubit state. When the representative photon detection count for a time step is in the dark detection region 430, it may be determined with the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) that the qubit being read is in the dark qubit state. When the representative photon detection count for a time step is in the ambiguous detection region 420, the qubit state of the qubit is not determinable the selected accuracy (e.g., confidencelevel, likelihood ratio, Bayesian likelihood ratio, and / or the like) that the qubit being read is in the bright qubit state. The representative photon detection counts of Figure 4A are cumulative photon detection counts.

[0101] The bright state thresholds 402 and the dark state thresholds 404 illustrated in Figure 4 A are determined using a constant a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). For example, the same a selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) is used to determine the bright state thresholds 402 and the dark state thresholds 404 at each time step. In some instances, this may result in the representative photon detection count at the final time step (e.g., tio as illustrated) being in the ambiguous detection region 420. In such an instance, a third threshold or other technique may be used to determine whether the qubit is in the bright qubit state or the dark qubit state. In some such instances, it may be determined that the result of the qubit reading operation is inconclusive (e.g., the qubit state of the qubit is not able to be determined based on the representative photon detection count).

[0102] Figure 4B provides a plot 400B that illustrates another example of bright state thresholds 402 and dark state thresholds 404. The bright state thresholds 402 and the dark state thresholds 404 are determined such that, at the final time step (e.g., tio as illustrated), the bright state threshold 402 and the dark state threshold 404 are equal to one another. In other words, at the final time step, the representative photon detection counts is either in the bright detection region (e.g., greater than the bright state threshold 402 corresponding to the final time step) or in the dark detection region (e.g., less than or equal to the dark state threshold 404 corresponding to the final time step). In an example embodiment, the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) used to determine the bright state thresholds and the dark state thresholds is different for different time steps. For example, the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) used to determine the bright state thresholds and the dark state thresholds may be lower at the final time step (e.g., tio as illustrated) than at the initial time step to. For example, the evolution of the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) used to determine the bright state thresholds and the dark state thresholds with respect to time is configured such that, at the final time step, the bright state threshold is equal to the dark state threshold.

[0103] While Figures 4A and 4B illustrate the set length of time being divided into eleven time steps to - tio, fewer or more time steps may be used in various embodiments.

[0104] Returning to Figure 3, at step 304, the computing entity 10 and / or the controller 30 provides and / or stores the dark state thresholds and the bright state thresholds for the plurality of time steps. In an example embodiment, the computing entity 10 and / or the controller 30 stores the dark state thresholds and the bright state thresholds as a look up table indexed by time step. Various datastore architectures may be used to store the dark state thresholds and the bright state thresholds for the plurality of time steps in various embodiments.

[0105] In an example embodiment where the dark state thresholds and the bright state thresholds were determined by the computing entity 10, the computing entity 10 provides (e.g., transmits) the dark state thresholds and the bright state thresholds for the plurality of time steps (possibly in the form of a look up table or other datastore architecture) such that the controller 30 receives the dark state thresholds and the bright state thresholds for the plurality of time steps. For example, the computing entity 10 may cause the controller 30 to store the dark state thresholds and the bright state thresholds for the plurality of time steps to memory local to and / or accessible to the controller 30 (e.g., memory 610).

[0106] For example, the computing entity 10 and / or the controller 30 comprise means, such as processing devices 605, 708, memories 610, 722, 724, communication interfaces 620, 720, and / or the like for causing the controller 30 to store the dark state thresholds and the bright state thresholds for the plurality of time steps as a look up table or in another datastore architecture.

[0107] Figure 5 provides a flowchart illustrating various processes, procedures, and / or the like for performing a qubit reading operation and / or for determining a quantum state of a quantum object (e.g., the qubit state of a qubit). In various embodiments, the steps of Figure 5 are performed by a controller 30 of a system confining the quantum objects (e.g., quantum computer 110). In an example embodiment, one or more steps of Figure 5 are performed by a computing entity 10.

[0108] Starting at step 502, the controller 30 causes the quantum computer 110 to start performing a qubit reading operation on a qubit. For example, the controller 30 may cause the qubit reading operation to be performed as part of a quantum circuit and / or program being performed and / or executed by the quantum computer 110, as part of a calibration procedure, as part of a syndrome measurement, and / or the like. In various embodiments, the controller 30 controls operation of a manipulation source 60 to cause the manipulation source 60 to start to generate and / or provide a reading manipulation signal such that the reading manipulation signal is incident on the qubit to be read. For example, the qubit on which the qubit readingoperation is to be performed may be confined at a target location defined at least in part by the confinement apparatus 70. The controller 30 may control operation of the manipulation source 60 and / or one or more active components of a respective beam path system 66 to cause the reading manipulation signal to be incident on the qubit at the target location. For example, the controller 30 comprises means, such as processing device 605, memory 610, driver controller elements 615, and / or the like, to cause the quantum computer 110 to start performing a qubit reading operation on a qubit.

[0109] At step 504, the controller obtains a photon detection count for a time step of the qubit reading operation. For example, one or more photodetectors of the optics collection system 80 provide sensor signals for receipt by the controller 30. The one or more sensor signals encode and / or indicate the number of photons detected by the respective photodetector. For example, the controller 30 extracts the photon detection count for a time step from the one or more sensor signals received by the controller 30. For example, the controller 30 may count the number of photons detected during a sampling time corresponding to the time step as indicated by the one or more sensor signals to determine a photon detection count for the time step. In various embodiments, the controller 30 comprises means, such as processing device 605, memory 610, A / D converter 625, and / or the like, for obtaining a photon detection count for a time step of the qubit reading operation.

[0110] At step 506, the controller 30 evaluates dark threshold criteria and / or bright threshold criteria based at least in part on the photon detection count for the time step. For example, the controller 30 determines a representative photon detection count for the time step based on the photon detection count for the time step. For example, the controller 30 comprises means, such as processing device 605, memory 610, and / or the like, for evaluating the dark threshold criteria and / or the bright threshold criteria based at least in part on the photon detection count for the time step.

[0111] For example, the controller 30 may determine a representative photon detection count based at least in part on the photon detection count for the time step. In various embodiments, the representative photon detection count is a cumulative photon detection count, average photon detection count, individual time step photon detection count, a sliding window sum of photon detection counts, and / or the like. In an example embodiment, a cumulative photon detection count for the ith time step Ni is the sum of the photon detection counts nk detected during each time step through the ith time step (N^ = k=onk)- Inanexample embodiment, the average photon detection count for the ith time step ntis theaverage photon count detection of the photon detection count nk during each time step through the ith time step (nt= fc=onk / (i + 1))-

[0112] The controller 30 access and / or reads a bright state threshold and a dark state threshold corresponding to the time step (e.g., from memory 610). For example, the controller 30 may access and / or read the bright state threshold corresponding to the time step and the dark state threshold corresponding to the time step from a look up table stored in memory 610.

[0113] The controller 30 compares the representative photon detection count (determined based at least in part on the photon detection count for the time step) to the dark state threshold and / or the bright state threshold. For example, in some instances evaluating the dark threshold criteria and / or the bright threshold criteria includes comparing the representative photon detection count corresponding to the time step to the dark state threshold corresponding to the time step and / or comparing the representative photon detection count corresponding to the time step to the bright state threshold corresponding to the time step. For example, evaluating the dark threshold criteria includes determining whether the representative photon detection count corresponding to the time step is greater than, equal to, or less than the dark state threshold corresponding to the time step, in an example embodiment. For example, evaluating the bright threshold criteria includes determining whether the representative photon detection count corresponding to the time step is greater than, equal to, or less than the bright state threshold corresponding to the time step, in an example embodiment.

[0114] At step 508, the controller 30 determines whether the dark threshold criteria or the bright threshold criteria is satisfied at the time step. For example, the controller 30 determines whether the dark threshold criteria is satisfied at the time step based at least in part on the evaluation of the dark threshold criteria. For example, the controller 30 determines whether the bright threshold criteria is satisfied at the time step based at least in part on the evaluation of the bright threshold criteria. For example, the controller 30 comprises means, such as processing device 605, memory 610, and / or the like, for determining whether the dark threshold criteria or the bright threshold criteria is satisfied.

[0115] In an example embodiment, the controller 30 determines that the bright threshold criteria is satisfied when the representative photon detection count corresponding to the time step is greater than or equal to the bright state threshold corresponding to the time step. In an example embodiment, the controller 30 determines that the dark threshold criteria is satisfiedwhen the representative photon detection count corresponding to the time step is less than the dark state threshold corresponding to the time step.

[0116] In an example embodiment, the controller 30 determines that the bright threshold criteria is satisfied when the representative photon detection count corresponding to the time step is greater than the bright state threshold corresponding to the time step. In an example embodiment, the controller 30 determines that the dark threshold criteria is satisfied when the representative photon detection count corresponding to the time step is less than or equal to the dark state threshold corresponding to the time step.

[0117] When it is determined, at step 508, that the bright threshold criteria is satisfied, the process continues to step 512. At step 512, responsive to determining that the bright threshold criteria is satisfied, the controller 30 determines that the qubit is in the bright qubit state. For example, the controller 30 may determine that the representative photon detection count is located in the bright detection region 410. For example, the controller 30 may store in memory 610 an indication that the qubit was determined to be in the bright qubit state. For example, the controller 30 comprises means, such as processing device 605, memory 610, and / or the like for determining that the qubit in the bright qubit state. In an example embodiment, the controller 30 may determine that the bright threshold criteria is satisfied for at least two consecutive time steps before determining that the qubit is in the bright qubit state.

[0118] When it is determined at step 508, that the dark threshold criteria is satisfied the process continues to step 514. At step 514, responsive to determining that the dark threshold criteria is satisfied, the controller 30 determines that the qubit is in the dark qubit state. For example, the controller 30 may determine that the representative photon detection count is located in the dark detection region 430. For example, the controller 30 may store in memory 610 an indication that the qubit was determined to be in the dark qubit state. For example, the controller 30 comprises means, such as processing device 605, memory 610, and / or the like for determining that the qubit in the dark qubit state. In an example embodiment, the controller 30 may determine that the dark threshold criteria is satisfied for at least two consecutive time steps before determining that the qubit is in the dark qubit state.

[0119] When it is determined at step 508, that neither the bright threshold criteria nor the dark threshold criteria are satisfied, the process continues to step 510. For example, responsive to determining that neither the bright threshold criteria nor the dark threshold criteria are satisfied, the controller 30 may determine that a determination of the qubit state of the qubit cannot be determined at the time step. For example, the controller 30 may determinethat the representative photon detection count corresponding to the time step is located in the ambiguous detection region 420.

[0120] In an example embodiment, responsive to determining that neither the bright threshold criteria nor the dark threshold criteria are satisfied, the controller 30 may determine, whether the amount of time for which the qubit reading operation has been performed is less than a maximum reading time (e.g., the set length of time of the qubit reading operation). For example, the controller 30 comprises means, such as processing device 605, memory 610, and / or the like for determining whether the amount of time for which the qubit reading operation has been performed is less than the maximum reading time.

[0121] Responsive to determining that the amount of time for which the qubit reading operation has been performed is less than the maximum reading time, the process returns to step 504. For example, the qubit reading operation is continued and the photon detection count for the next time step is obtained.

[0122] Responsive to determining that the amount of time for which the qubit reading operation has been performed is not less than the maximum reading time (e.g., greater than or equal to the maximum reading time), the process continues to step 516.

[0123] At step 516, responsive to determining that the amount of time for which the qubit reading operation has been performed is not less than the maximum reading time and that neither the bright threshold criteria nor the dark threshold criteria is satisfied, the controller 30 determines that the outcome of the qubit reading operation is ambiguous. For example, the controller 30 may determine that the qubit state of the qubit was not determined with the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like).

[0124] For example, the controller 30 may store the photon detection count for each time step, a representative photon detection count for each time step, a representative photon detection count for the final time step, and / or the like in memory 610 for processing using another qubit state determination technique. In another example, the controller 30 may provide (e.g., transmit) the photon detection count for each time step, a representative photon detection count for each time step, a representative photon detection count for the final time step, and / or the like for receipt by a computing entity 10 for processing using another qubit state determination technique.

[0125] At step 518, responsive to determining that the qubit is in the bright qubit state, the dark qubit state, or that the outcome of the qubit reading operation is ambiguous (after performing the qubit reading operation for the maximum reading time / set length of time), thecontroller 30 causes the performance of the qubit reading operation to stop, halt, and / or be concluded. For example, the controller 30 may control operation of the manipulation source 60 and / or corresponding beam path system 66 to cause the reading manipulation signal to stop being incident on the qubit. For example, the controller 30 may control operation of the manipulation source 60 to cause the manipulation source 60 to stop generating and / or providing the reading manipulation signal. In another example, the controller 30 controls one or more active components of a beam path system 66 to cause the reading manipulation signal to stop being incident on and / or applied to the target location where the qubit is located. For example, the controller 30 comprises means, such as processing device 605, memory 610, driver controller elements 615, and / or the like, to cause the quantum computer 110 to stop, halt, and / or conclude performance of the qubit reading operation on the qubit.

[0126] As should be understood, in various scenarios, the qubit state of the qubit may be determined at an ith time step ti that is before the final time step tf (e.g., ti < tf). In these scenarios, the performance of the qubit reading operation may be stopped, halted, and / or concluded prior to the execution of the qubit reading operation for the entire set length of time. For example, the reading manipulation signal may be provided to the target location where the qubit is located for less than the set length of time. This results in reduced crosstalk errors and reduced detection errors due to state mixing and / or the like.

[0127] At step 520, the controller 30 stores and / or provides the result of performing the qubit reading operation. For example, the controller 30 may store the result of performing the qubit reading operation in memory 610. For example, the controller 30 may store an indication of whether the qubit was in the bright qubit state or the dark qubit state in memory 610. In another example, the controller 30 may provide (e.g., transmit) the result of performing the qubit reading operation for receipt by the computing entity 10. For example, the controller 30 may provide (e.g., transmit) an indication of whether the qubit was in the bright qubit state or the dark qubit state for receipt by the computing entity 10.

[0128] In various embodiments, the confinement apparatus 70 defines a plurality of target locations and confines a plurality of qubits. In such embodiments, qubit reading operations may be performed at one or more target locations in parallel and / or at least partially simultaneously (e.g., at least partially overlapping in time). For example, qubit reading operations may start being performed in multiple target locations at the same time. The qubit reading operations in each of the multiple target locations may end for each of the multiple target locations at the same time (e.g., once the qubit state of each of the qubits being read has been determined) or may be ended individually (e.g., once the qubit state of a qubit at aparticular target location is determined, the qubit reading operation may stop being performed at the particular target location).Technical Advantages

[0129] Conventional qubit reading operations for QCCD-based quantum computers include applying a laser beam to the qubit to be read. When the qubit is in a “bright” qubit state, the laser beam being incident on the qubit causes the qubit to fluoresce. When the qubit is in a “dark” qubit state, the laser beam being incident on the qubit does not cause the qubit to fluoresce. By counting the number of photons detected over a set length of time and comparing that number to a set threshold value, a determination of whether the qubit is in the bright qubit state or the dark qubit state is made. The set length of time needs to be long enough for the determination to be made with the selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). However, the longer the laser beam is on (e.g., the longer the set length of time), the more opportunity there is for the laser beam to cause cross-talk errors or for state mixing to result in a detection error (e.g., determining an incorrect qubit state for the qubit).

[0130] Previous attempts to enable shorter qubit reading operation performance times (e.g., adaptive detection methods) tend to be too computationally costly to perform in realtime and / or use approximations to enable real-time use but that sacrifice the precision of the detection. Therefore, technical problems exist regarding how to reduce the amount of time that the qubit reading operation is performed without sacrificing the precision and / or the confidence level with which the qubit state is determined.

[0131] Various embodiments provide technical solutions to these technical problems. For example, in various embodiments, the time-dependent bright threshold requirement and timedependent dark threshold requirement are pre-determined to provide qubit state determination with a desired and / or selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like). Thus, the precision of qubit state determinations in accordance with various embodiments satisfy the desired accuracy requirements of the particular application. Moreover, for each time step, a bright state threshold and a dark state threshold corresponding to the threshold are read and the representative photon detection count corresponding to the time step is compared to one or both of the bright state threshold and the dark state threshold corresponding to the time step. Therefore, minimal computational resources are required to perform the adaptive detection in real-time during performance of the qubit reading operation.

[0132] As a result of being able to perform the adaptive detection in real-time during performance of the qubit reading operation, it is possible to determine the state of the qubit with a desired and / or selected accuracy (e.g., confidence level, likelihood ratio, Bayesian likelihood ratio, and / or the like) after a time period of performing the qubit reading operation that is less than the set length of time, in various instances. Once the state of the qubit is determined with the desired level of confidence, performance of the qubit reading operation may be stopped, halted, or concluded even if the qubit reading operation has not yet been performed for the set length of time. This results int the reading manipulation signal being provided and / or applied to the qubit for a shorter amount of time than the set length of time, in various instance. As such, cross-talk errors and detection errors (e.g., due to state mixing, etc.) are reduced.

[0133] Thus, various embodiments provide technical improvements to the fields of quantum computing, qubit reading operations, quantum state determination, and similar fields.Example Controller

[0134] In various embodiments, a system, such as a quantum computer 110, is configured to determine the quantum state of a quantum object. For example, a quantum computer 110 may be configured to perform a qubit reading operation on a qubit to determine the qubit state of the qubit. In various embodiments, the system (e.g., quantum computer 110) comprises a controller 30 configured to control various components of the system and / or to determine respective quantum states of one or more quantum objects (e.g., qubit states of one or more qubits) based on sensor signals generated as part of performing a qubit reading operation.

[0135] In various embodiments, the controller 30 is configured to control various components of the system (e.g., quantum computer 110). For example, the controller 30 may be configured to control the voltage sources 50, a cryostat system and / or vacuum system controlling the temperature and pressure within the cryostat and / or vacuum chamber 40, manipulation sources 60, a cooling system, and / or other systems controlling the environmental conditions (e.g., temperature, humidity, pressure, and / or the like) within the cryostat and / or vacuum chamber 40 and / or configured to manipulate and / or cause a controlled evolution of quantum states of one or more quantum objects within the confinement apparatus. In various embodiments, the controller 30 may be configured to receive sensor signals from one or more optics collection systems 80.

[0136] As shown in Figure 6, in various embodiments, the controller 30 may comprise various controller elements including processing devices 605, memory 610, driver controller elements 615, a communication interface 620, analog-digital converter elements 625, and / or the like. For example, the processing devices 605 may comprise programmable logic devices (CPLDs), microprocessors, coprocessing entities, application-specific instruction-set processors (ASIPs), integrated circuits, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), programmable logic arrays (PLAs), hardware accelerators, other processing devices and / or circuitry, and / or the like. The term circuitry may refer to an entirely hardware embodiment or a combination of hardware and computer program products. In an example embodiment, the processing device 605 of the controller 30 comprises a clock and / or is in communication with a clock.

[0137] For example, the memory 610 may comprise non-transitory memory such as volatile and / or non-volatile memory storage such as one or more of as hard disks, ROM, PROM, EPROM, EEPROM, flash memory, MMCs, SD memory cards, Memory Sticks, CBRAM, PRAM, FeRAM, RRAM, SONOS, racetrack memory, RAM, DRAM, SRAM, FPM DRAM, EDO DRAM, SDRAM, DDR SDRAM, DDR2 SDRAM, DDR3 SDRAM, RDRAM, RIMM, DIMM, SIMM, VRAM, cache memory, register memory, and / or the like. In various embodiments, the memory 610 may store a queue of commands to be executed to cause a quantum algorithm and / or circuit to be executed (e.g., an executable queue), qubit records corresponding the qubits of quantum computer (e.g., in a qubit record data store, qubit record database, qubit record table, and / or the like), a calibration table, computer program code (e.g., in a one or more computer languages, specialized controller language(s), and / or the like), and / or the like. In an example embodiment, execution of at least a portion of the computer program code stored in the memory 610 (e.g., by a processing device 605) causes the controller 30 to perform one or more steps, operations, processes, procedures and / or the like described herein for performing a qubit reading operation and / or to determine a qubit state of a qubit based at least in part on photon detection counts for one or more time steps during performance of the qubit reading operation.

[0138] In an example embodiment, the memory 610 stores bright state thresholds and dark state thresholds corresponding to a plurality of time steps of a qubit reading operation. The bright state thresholds and dark state thresholds corresponding to the plurality of time steps may be stored as a look up table, database, and / or other architecture of datastore.

[0139] In various embodiments, the driver controller elements 615 may include one or more drivers and / or controller elements each configured to control one or more drivers. Invarious embodiments, the driver controller elements 615 may comprise drivers and / or driver controllers. For example, the driver controllers may be configured to cause one or more corresponding drivers to be operated in accordance with executable instructions, commands, and / or the like scheduled and executed by the controller 30 (e.g., by the processing device 605). For example, the driver controller elements 615 comprise one or more drivers and / or controller elements configured to control operation of a manipulation source 60 configured to generate and / or provide a reading manipulation signal. In various embodiments, the driver controller elements 615 may enable the controller 30 to operate a voltage sources 50, manipulation sources 60, cooling system, and / or the like. In various embodiments, the drivers may be laser drivers; vacuum component drivers; drivers for controlling the flow of current and / or voltage applied to electrodes used for maintaining and / or controlling the trapping potential of the confinement apparatus 70 (and / or other drivers for providing driver action sequences to potential generating elements of the confinement apparatus); cryostat and / or vacuum system component drivers; cooling system drivers, and / or the like.

[0140] In various embodiments, the controller 30 comprises means for communicating and / or receiving sensors signals from one or more optical receiver components (e.g., photodetectors of the optics collection system 80). For example, the controller 30 may comprise one or more analog-digital converter elements 625 configured to receive signals from one or more optical receiver components (e.g., a photodetector of the optics collection system 80), calibration sensors, and / or the like.

[0141] In various embodiments, the controller 30 may comprise a communication interface 620 for interfacing and / or communicating with a computing entity 10. For example, the controller 30 may comprise a communication interface 620 for receiving executable instructions, command sets, and / or the like from the computing entity 10 and providing output received from the quantum computer 110 (e.g., from an optical collection system) and / or the result of a processing the output to the computing entity 10. In various embodiments, the computing entity 10 and the controller 30 may communicate via a direct wired and / or wireless connection and / or via one or more wired and / or wireless networks 20.Exemplary Computing Entity

[0142] Figure 7 provides an illustrative schematic representative of an example computing entity 10 that can be used in conjunction with embodiments of the present invention. In various embodiments, a computing entity 10 is configured to allow a user toprovide input to the quantum computer 110 (e.g., via a user interface of the computing entity 10) and receive, display, analyze, and / or the like output from the quantum computer 110.

[0143] As shown in Figure 7, a computing entity 10 can include an antenna 712, a transmitter 704 (e.g., radio), a receiver 706 (e.g., radio), and a processing device 708 that provides signals to and receives signals from the transmitter 704 and receiver 706, respectively. The signals provided to and received from the transmitter 704 and the receiver 706, respectively, may include signaling information / data in accordance with an air interface standard of applicable wireless systems to communicate with various entities, such as a controller 30, other computing entities 10, and / or the like. In this regard, the computing entity 10 may be capable of operating with one or more air interface standards, communication protocols, modulation types, and access types. For example, the computing entity 10 may be configured to receive and / or provide communications using a wired data transmission protocol, such as fiber distributed data interface (FDDI), digital subscriber line (DSL), Ethernet, asynchronous transfer mode (ATM), frame relay, data over cable service interface specification (DOCSIS), or any other wired transmission protocol. Similarly, the computing entity 10 may be configured to communicate via wireless external communication networks using any of a variety of protocols, such as general packet radio service (GPRS), Universal Mobile Telecommunications System (UMTS), Code Division Multiple Access 2000 (CDMA2000), CDMA2000 IX (IxRTT), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA), Long Term Evolution (LTE), Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Evolution-Data Optimized (EVDO), High Speed Packet Access (HSPA), High-Speed Downlink Packet Access (HSDPA), IEEE 802.11 (Wi-Fi), Wi-Fi Direct, 802.16 (WiMAX), ultra wideband (UWB), infrared (IR) protocols, near field communication (NFC) protocols, Wibree, Bluetooth protocols, wireless universal serial bus (USB) protocols, and / or any other wireless protocol. The computing entity 10 may use such protocols and standards to communicate using Border Gateway Protocol (BGP), Dynamic Host Configuration Protocol (DHCP), Domain Name System (DNS), File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), HTTP over TLS / SSL / S ecure, Internet Message Access Protocol (IMAP), Network Time Protocol (NTP), Simple Mail Transfer Protocol (SMTP), Telnet, Transport Layer Security (TLS), Secure Sockets Layer (SSL), Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP),Datagram Congestion Control Protocol (DCCP), Stream Control Transmission Protocol (SCTP), HyperText Markup Language (HTML), and / or the like.

[0144] Via these communication standards and protocols, the computing entity 10 can communicate with various other entities using concepts such as Unstructured Supplementary Service information / data (USSD), Short Message Service (SMS), Multimedia Messaging Service (MMS), Dual-Tone Multi-Frequency Signaling (DTMF), and / or Subscriber Identity Module Dialer (SIM dialer). The computing entity 10 can also download changes, add-ons, and updates, for instance, to its firmware, software (e.g., including executable instructions, applications, program modules), and operating system.

[0145] In various embodiments, the computing entity 10 may comprise a communication interface 720 for interfacing and / or communicating with one or more other (classical and / or semiconductor-based) computing entities 10 and / or controller 30.

[0146] The computing entity 10 may also comprise a user interface device comprising one or more user input / output interfaces (e.g., a display 716 and / or speaker / speaker driver coupled to a processing device 708 and a touch screen, keyboard, mouse, and / or microphone coupled to a processing device 708). For instance, the user output interface may be configured to provide an application, browser, user interface, interface, dashboard, screen, webpage, page, and / or similar words used herein interchangeably executing on and / or accessible via the computing entity 10 to cause display or audible presentation of information / data and for interaction therewith via one or more user input interfaces. The user input interface can comprise any of a number of devices allowing the computing entity 10 to receive data, such as a keypad 718 (hard or soft), a touch display, voice / speech or motion interfaces, scanners, readers, or other input device. In embodiments including a keypad 718, the keypad 718 can include (or cause display of) the conventional numeric (0-9) and related keys (#, *), and other keys used for operating the computing entity 10 and may include a full set of alphabetic keys or set of keys that may be activated to provide a full set of alphanumeric keys. In addition to providing input, the user input interface can be used, for example, to activate or deactivate certain functions, such as screen savers and / or sleep modes. Through such inputs the computing entity 10 can collect information / data, user interaction / input, and / or the like.

[0147] The computing entity 10 can also include volatile storage or memory 722 and / or non-volatile storage or memory 724, which can be embedded and / or may be removable. For instance, the non-volatile memory may be ROM, PROM, EPROM, EEPROM, flash memory, MMCs, SD memory cards, Memory Sticks, CBRAM, PRAM,FeRAM, RRAM, SONOS, racetrack memory, and / or the like. The volatile memory may be RAM, DRAM, SRAM, FPM DRAM, EDO DRAM, SDRAM, DDR SDRAM, DDR2 SDRAM, DDR3 SDRAM, RDRAM, RIMM, DIMM, SIMM, VRAM, cache memory, register memory, and / or the like. The volatile and non-volatile storage or memory can store databases, database instances, database management system entities, data, applications, programs, program modules, scripts, source code, object code, byte code, compiled code, interpreted code, machine code, executable instructions, and / or the like to implement the functions of the computing entity 10.Conclusion

[0148] Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

CLAIMS1. A method for determining a result of a qubit reading operation, the method comprising:obtaining, by a processing device, a photon detection count for a time step of the qubit reading operation performed on a qubit; andbased at least in part on the photon detection count for the time step, determining, by the processing device, whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied, wherein:responsive to determining that the bright threshold criteria is satisfied, an indication that the qubit is in a bright state is stored;responsive to determining that the dark threshold criteria is satisfied, an indication that the qubit is in a dark state is stored; andresponsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, a state of the qubit is undetermined.

2. The method of claim 1, wherein the time step is one of a plurality of time steps.

3. The method of claim 2, wherein determining at least one of whether the bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied comprises:determining a representative photon detection count based at least in part on the photon detection count for the time step; andcomparing the representative photon detection count to at least one of a bright state threshold corresponding to the time step or a dark state threshold corresponding to the time step.

4. The method of claim 3, wherein determining at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied further comprises:responsive to determining that the representative photon detection count is greater than the bright state threshold corresponding to the time step, determining that the qubit is in the bright state;responsive to determining that the representative photon detection count is less than or equal to the dark state threshold corresponding to the time step, determining that the qubit is in the dark state; andresponsive to determining that the representative photon detection count is less than or equal to the bright state threshold corresponding to the time step and greater than the dark state threshold corresponding to the time step, determining that the state of the qubit is undetermined.

5. The method of claim 1, further comprising responsive to determining that the qubit is in the dark state or to determining that the qubit is in the bright state, causing the qubit reading operation to stop being performed.

6. The method of claim 5, further comprising, responsive to determining that the state of the qubit is undetermined, causing the qubit reading operation to continue being performed.

7. The method of claim 1, further comprising:responsive to determining that the state of the qubit is undetermined, determining whether an amount of time for which the qubit reading operation has been performed has reached a maximum reading operation duration; andresponsive to determining that the amount of time for which the qubit reading operation has been performed has reached the maximum reading operation duration, causing the performance of the qubit reading operation to stop.

8. The method of claim 1, wherein the bright threshold criteria and the dark threshold criteria are stored in a non-transitory memory accessible to the processing device.

9. The method of claim 8, wherein the bright threshold criteria and the dark threshold criteria are stored as one or more look up tables and the processing device comprises a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC) configured to determine at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied.

10. The method of claim 8, wherein the bright threshold criteria and the dark threshold criteria are defined based at least in part on one or more simulations of a qubit reading operation and a selected accuracy.

11. The method of claim 10, wherein the selected accuracy is a function of a reading operation duration such that at a maximum reading operation duration a bright state threshold of the bright threshold criteria is equal to a dark state threshold of the dark threshold criteria.

12. The method of claim 1, further comprising accessing a bright state threshold corresponding to the time step and accessing a dark state threshold corresponding to the time step, wherein the bright state threshold corresponding to the time step is used to determine whether the bright threshold criteria are satisfied and the dark state threshold corresponding to the time step is used to determine whether the dark threshold criteria are satisfied.

13. A controller comprising a processing device and a memory, the controller configured to perform at least:obtaining a photon detection count for a time step of the qubit reading operation performed on a qubit; andbased at least in part on the photon detection count for the time step, determining whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied, wherein:responsive to determining that the bright threshold criteria is satisfied, an indication that the qubit is in a bright state is stored in the memory;responsive to determining that the dark threshold criteria is satisfied, an indication that the qubit is in a dark state is stored in the memory; and responsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, a state of the qubit is undetermined.

14. The controller of claim 13, wherein the time step is one of a plurality of time steps and determining at least one of whether the bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied comprises:determining a representative photon detection count based at least in part on the photon detection count for the time step; andcomparing the representative photon detection count to at least one of a bright state threshold corresponding to the time step or a dark state threshold corresponding to the time step.

15. The controller of claim 14, wherein determining at least one of whether the bright threshold criteria is satisfied or whether the dark threshold criteria is satisfied further comprises:responsive to determining that the representative photon detection count is greater than the bright state threshold corresponding to the time step, determining that the qubit is in the bright state;responsive to determining that the representative photon detection count is less than or equal to the dark state threshold corresponding to the time step, determining that the qubit is in the dark state; andresponsive to determining that the representative photon detection count is less than or equal to the bright state threshold corresponding to the time step and greater than the dark state threshold corresponding to the time step, determining that the state of the qubit is undetermined.

16. The controller of claim 13, wherein the controller is further configured to perform, responsive to determining that the qubit is in the dark state or to determining that the qubit is in the bright state, causing the qubit reading operation to stop being performed and, responsive to determining that the state of the qubit is undetermined, causing the qubit reading operation to continue being performed.

17. The controller of claim 13, wherein the controller is further configured to perform: responsive to determining that the state of the qubit is undetermined, determining whether an amount of time for which the qubit reading operation has been performed has reached a maximum reading operation duration; andresponsive to determining that the amount of time for which the qubit reading operation has been performed has reached the maximum reading operation duration, causing the performance of the qubit reading operation to stop.

18. A system comprising:a confinement apparatus configured to confine a plurality of quantum objects;a manipulation source configured to generate and provide at least one manipulation signal;an optics collection system comprising at least one photodetector configured to detect photons fluoresced by a qubit of the plurality of quantum objects, wherein the optics collection system is configured to generate a sensor signal corresponding to detection of photons by the photodetector and provide the sensor signal to a controller; andthe controller configured to control operation of the confinement apparatus and the manipulation source and to receive one or more sensor signals generated by the optics collection system, the controller configured to perform at least:obtaining a photon detection count for a time step of the qubit reading operation performed on a qubit;based at least in part on the photon detection count for the time step, determining whether a bright threshold criteria is satisfied or whether a dark threshold criteria is satisfied, wherein:responsive to determining that the bright threshold criteria is satisfied, an indication that the qubit is in a bright state is stored;responsive to determining that the dark threshold criteria is satisfied, an indication that the qubit is in a dark state is stored; andresponsive to determining that neither the bright threshold criteria nor the dark threshold criteria is satisfied, a state of the qubit is undetermined.

19. The system of claim 18, wherein the controller is further configured to control operation of the manipulation source to cause the manipulation source to generate a reading manipulation signal and provide the reading manipulation signal such that the reading manipulation signal is incident on the qubit.

20. The system of claim 18, wherein the controller is further configured to determine the photon detection count for the time step based at least in part on the one or more sensor signals.

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