Observation and evaluation system, observation and evaluation method, and program

Abstract

The present invention provides an observation and evaluation system that makes it easier to determine whether each of the multiple atoms constituting an atomic array is a single atom or not. [Solution] The observation and evaluation system 10 is an observation and evaluation system 10 that evaluates the unity of photons in order to determine whether or not multiple atoms 201 are arranged in a two-dimensional array, and comprises a sensor 20 in which multiple pixels 21 having a multiplication function are arranged in a two-dimensional array and expose the light emitted by multiple atoms 201 all at once, a control unit 30 that controls the multiple pixels 21 to be exposed for multiple exposure periods, and an evaluation unit 40 that evaluates the unity of photons contained in the light by comparing the detection results for multiple exposure periods.

Description

Technical Field

[0001] The present disclosure relates to an observation and evaluation system, an observation and evaluation method, and a program.

Background Art

[0002] A quantum computer is a computer that performs parallel calculations using qubits in a superposition state of two values, 0 and 1. A quantum computer of a cold atom method that uses cold atoms as elements for realizing qubits is known.

[0003] Furthermore, by arraying cold atoms (that is, arranging a plurality of cold atoms in a two-dimensional array), information processing can be performed at a higher bit rate.

[0004] Patent Document 1 discloses a technique for arranging atoms in a two-dimensional array by an array trap.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to the technique disclosed in Patent Document 1 and the like, when atoms are arranged in a two-dimensional array, the atom array must be composed of single atoms. In other words, there should not be 0 or a plurality of atoms at a position where one atom should exist.

[0007] Whether an atom is a single atom can be determined by evaluating whether the light emitted from the atom consists of a single photon. However, since an atomic array is composed of multiple atoms, confirming that an atomic array is composed of single atoms is time-consuming.

[0008] This disclosure aims to provide an observation and evaluation system, an observation and evaluation method, and a program that can more easily determine whether each of the multiple atoms constituting an atomic array is a single atom or not. [Means for solving the problem]

[0009] One aspect of the observation and evaluation system according to this disclosure is an observation and evaluation system for evaluating the unity of photons in order to determine whether or not a plurality of atoms are arranged in a two-dimensional array, comprising: a sensor having a multiplication function and having a plurality of pixels arranged in a two-dimensional array that expose the light emitted by the plurality of atoms all at once; a control unit that controls the plurality of pixels to be exposed for a plurality of exposure periods; and an evaluation unit that evaluates the unity of photons contained in the light by comparing the detection results for the plurality of exposure periods.

[0010] Furthermore, one aspect of the observation and evaluation method relating to this disclosure is an observation and evaluation method for evaluating the unity of photons in order to determine whether a plurality of atoms executed by a computer are arranged in a two-dimensional array, and includes a control step of controlling a plurality of exposure periods for detecting light emitted by the plurality of atoms; a detection step of detecting the light by exposing a plurality of pixels having a multiplication function arranged in a two-dimensional array for the plurality of exposure periods; and an evaluation step of evaluating the unity of photons contained in the light by comparing the detection results for the plurality of exposure periods.

[0011] Furthermore, this disclosure can be implemented not only as the observation and evaluation method described above, but also as a program that causes a computer to execute the observation and evaluation method. Moreover, it can also be implemented as a computer-readable recording medium storing that program. [Effects of the Invention]

[0012] The observation and evaluation system, observation and evaluation method, and program described herein make it easier to determine whether each of the multiple atoms constituting an atomic array is a single atom or not. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 illustrates the properties of a single cooled atom. [Figure 2] Figure 2 illustrates an example of a method for evaluating the unity of photons. [Figure 3] Figure 3 is a diagram illustrating the overview of the observation and evaluation system according to the embodiment. [Figure 4] Figure 4 is a block diagram showing the functional configuration of the observation and evaluation system according to the embodiment. [Figure 5] Figure 5 is a flowchart illustrating the overall operation, including the observation and evaluation system according to the embodiment. [Figure 6] Figure 6 is a flowchart illustrating the operation of the observation and evaluation system according to the embodiment. [Figure 7] Figure 7 is a diagram illustrating multiple groups of pixels according to the embodiment. [Figure 8] Figure 8 is a diagram illustrating the timing of multiple exposure periods according to the embodiment. [Figure 9] Figure 9 illustrates how photons are exposed during multiple exposure periods according to the embodiment. [Figure 10] Figure 10 is a graph showing the probability that the output combination when exposed during the period when a single photon arrives according to the embodiment is (0, 1) or (1, 0). [Figure 11] Figure 11 is a graph showing the probability that the output combination when exposed during the period when two photons arrive according to the embodiment will be (0, 1) or (1, 0). [Modes for carrying out the invention]

[0014] (Embodiment) Hereinafter, embodiments of the observation evaluation system, observation evaluation method, and program according to the present disclosure will be described in detail with reference to the drawings. Note that each of the embodiments described below shows a preferred specific example of the present disclosure. Numerical values, components, arrangement positions and connection forms of components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, components not described in the independent claims are described as optional components constituting a preferred form.

[0015] Note that each figure is a schematic diagram and is not necessarily drawn precisely. Also, in each figure, substantially the same configuration is denoted by the same reference numeral, and duplicate descriptions may be omitted or simplified.

[0016] In addition, ordinal numbers such as "first" and "second" in the present disclosure do not mean the number or order of components or the like unless otherwise specified, and are used for the purpose of avoiding confusion and distinguishing between the same type of components.

[0017] [Findings obtained by the inventor] The minimum unit of information (bit) in a normal computer is a binary value of 0 and 1. In contrast, the minimum unit of information (qubit) in a quantum computer is a superposition state of 0 and 1. A quantum computer can perform parallel calculations using qubits.

[0018] There are multiple types of quantum computers according to the elements that realize qubits. For example, the superconducting type, silicon type, optical type, ion trap type, and cold atom type are known.

[0019] In these quantum computers, cold atom-based quantum computers use laser-based optical tweezers to trap electrically neutral atoms and use them for quantum calculations. Since there is virtually no interaction between atoms when they remain electrically neutral, Rydberg-state atoms are used. Rydberg-state atoms are those in which the outermost electrons are excited to orbitals with high principal quantum numbers. While Rydberg-state atoms are electrically neutral overall, they have a high electric dipole moment due to the relatively long distance between the nucleus and electrons. Therefore, Rydberg-state atoms interact with each other. Each cold atom has a superposition state of nucleus spin and electron spin, and is used as a qubit.

[0020] The advantages of cold atom quantum computers include uniform qubit quality, long coherence time, relatively easy scaling up due to the use of optical tweezers technology, the ability to fully connect qubits, and the elimination of the need for dilution refrigerators.

[0021] In the setup phase of a cold atom quantum computer (i.e., the initial setup phase), cold atoms are arrayed in order to process information at a higher bitrate. In other words, an atomic array is formed by arranging multiple cold atoms in a two-dimensional array.

[0022] Herein, for a cold atom quantum computer to operate, the atomic array must be composed of single atoms. In other words, the cold atoms must be arranged one by one in a two-dimensional array. In the atomic array, there should not be zero or more atoms where one atom should be present. In this disclosure, an atomic array composed of single atoms is referred to as a single atom array.

[0023] Generally, to confirm that a cold atom is in a single-atomic state, the unity of photons is evaluated. Figure 1 is a diagram illustrating the properties of a single cold atom. Figure 2 is a diagram illustrating an example of a method for evaluating the unity of photons.

[0024] Figure 1 shows how a single cooled atom emits light when irradiated with an excitation light pulse. Specifically, when an excitation light pulse is irradiated onto a single cooled atom in the ground state, the atom enters an excited state. The cooled atom in the excited state emits a single photon and returns to the ground state. In other words, a single cooled atom emits one photon for each cycle in which it transitions from the ground state to the excited state and then returns to the ground state.

[0025] When a single cooled atom is continuously irradiated with excitation light pulses, the single cooled atom repeats the above cycle, emitting a single photon each time it transitions from the excited state to the ground state.

[0026] In this case, the interval between single-cold atoms emitting single photons is at least equal to the lifetime T of the excited state of the single-cold atom. For example, if the single-cold atom is a rubidium atom (hereinafter also referred to as a Rb atom), the lifetime T of the excited state is approximately 20 nsec. Therefore, single photons emitted from a single-cold atom exist at least T apart from each other. This state in which photons exist discretely is called photon antibunching.

[0027] Therefore, if a single photon is observed when a cold atom is irradiated with an excitation light pulse, then the cold atom can be said to be a single atom.

[0028] In other words, by observing photon antibunching, we can evaluate single-photon properties and confirm that the cooled atom emitting the photon is a single atom.

[0029] Figure 2 shows a conventional method for evaluating single-photon properties. As shown in Figure 2, a beam of light emitted from a light source is divided into two equal parts by a beam splitter, and the divided beams are received by two photon detectors at equal distances from the beam splitter. At this time, the timing t1 at which the light is received by one photon detector is changed while repeatedly receiving the light, and the timing t2 at which the light is received by the other photon detector is changed, and the correlation of the outputs of the two photon detectors is taken at time differences τ (=t1-t2). If the light emitted from the light source consists of single photons in a photon antibunching state, the intensity correlation function is a downward-facing convex function centered at τ=0.

[0030] In this way, single-photon properties can be evaluated from the shape of the graph obtained by measuring the time correlation of light emitted from a light source.

[0031] Here, in order to confirm that a cooled atom is a single atom by evaluating its single-photon property using the method shown in Figure 2, one beam splitter and two photon detectors are required for each cooled atom. Therefore, in order to confirm that all atoms constituting an atomic array are single atoms, a beam splitter equal to the number of arrays and twice the number of photon detectors are required, which leads to the problem of large-scale and high-cost equipment.

[0032] Therefore, the inventors conceived of an observation and evaluation system that can simultaneously determine whether each of the multiple atoms constituting an atomic array is a single atom or not.

[0033] An observation and evaluation system according to one aspect of the present disclosure is an observation and evaluation system for evaluating the unity of photons in order to determine whether or not a plurality of atoms are arranged in a two-dimensional array, comprising: a sensor having a multiplication function and having a plurality of pixels arranged in a two-dimensional array that expose the light emitted by the plurality of atoms all at once; a control unit that controls the plurality of pixels to be exposed for a plurality of exposure periods; and an evaluation unit that evaluates the unity of photons contained in the light by comparing the detection results for the plurality of exposure periods.

[0034] Such an observation and evaluation system makes it easier to determine whether each of the multiple atoms constituting an atomic array is a single atom or not. Figure 3 is a diagram showing an overview of the observation and evaluation system 10 according to an embodiment. As shown in Figure 3, the observation and evaluation system 10 includes a sensor 20 that receives photons emitted by atoms 201 constituting the atomic array 200.

[0035] The left side of Figure 3 shows a schematic diagram of the atomic array 200. In the atomic array 200, multiple atoms 201 are arranged in a two-dimensional array by an optical tweezers laser. For example, the optical tweezers laser is a laser that is shone to fix atoms 201 in a desired position. The optical tweezers laser is shone from multiple directions towards the desired position where atoms 201 are fixed. When an excitation laser is shone on atoms 201 fixed by the optical tweezers laser, atoms 201 emit photons. The excitation laser is a laser that is shone on atoms 201 to cause them to emit photons.

[0036] The atomic array 200 shown in Figure 3 is composed of four atoms 201, but the number of atoms 201 may be 50 or 100, and is not particularly limited. Also, in Figure 3, the optical tweezers laser and excitation laser are shown for one atom 201, but the optical tweezers laser and excitation laser irradiated for the other atoms 201 are not shown. All atoms 201 constituting the atomic array 200 are fixed by irradiation with the optical tweezers laser and irradiated with photons by irradiation with the excitation laser.

[0037] A schematic diagram of the sensor 20 is shown on the right side of Figure 3. In the sensor 20, multiple pixels 21 are arranged in a two-dimensional array. The pixels 21 receive photons emitted by atoms 201. The sensor 20 is arranged so that it can distinguish and receive photons emitted by each of the multiple atoms 201 that make up the atomic array 200. The circles shown as dots inside the sensor 20 in Figure 3 indicate the positions where photons are received in the sensor 20.

[0038] In this way, the observation and evaluation system 10 can simultaneously observe the photons emitted by each of the multiple atoms 201 that make up the atomic array 200 using the sensor 20.

[0039] The observation and evaluation system 10 can determine whether each of the multiple atoms 201 constituting the atomic array 200 is a single atom by evaluating the singularity of each of the multiple photons observed simultaneously.

[0040] [composition] The configuration of the observation and evaluation system 10 will now be described. Figure 4 is a block diagram showing the functional configuration of the observation and evaluation system 10 according to the embodiment.

[0041] The observation and evaluation system 10 is a system that simultaneously observes photons emitted by each of the multiple atoms 201 constituting the atomic array 200 using a sensor 20, and evaluates the unity of each of the multiple photons observed simultaneously. The observation and evaluation system 10 can evaluate whether or not the atomic array 200 is composed of single atoms. Specifically, the observation and evaluation system 10 comprises a sensor 20, a control unit 30, and an evaluation unit 40.

[0042] Sensor 20 is an array sensor that simultaneously exposes light emitted by multiple atoms 201. Sensor 20 is implemented by a multiplier array sensor capable of detecting single photons. The multiplier array sensor generates multiple signal charges by multiplying the single signal charge generated when a single photon is received, and outputs a pixel signal. Sensor 20 comprises multiple pixels 21 arranged in a two-dimensional array. The multiple pixels 21, for example, have the same configuration as each other.

[0043] Pixel 21 outputs a pixel signal based on the received light. Specifically, pixel 21 converts the received light into a signal charge, generates a pixel signal based on the converted signal charge, and outputs it.

[0044] Pixel 21 is realized by a photodetector such as a VAPD (Vertical Avalanche Photo Diode). Pixel 21 includes a multiplication unit that increases the number of electrons generated by a photon. The multiplication unit rapidly increases the number of electrons by, for example, causing the electrons generated by the diode that receives the photon to collide with atoms of a semiconductor crystal using a high electric field. As a result, pixel 21 can detect weak light such as a single photon.

[0045] Pixel 21 has the characteristics of high sensitivity and a small light-receiving area. More specifically, the pixel 21 realized by VAPD is sensitive enough to detect a single photon and has a small light-receiving area sufficient to distinguish and receive photons emitted by multiple atoms 201 constituting the atomic array 200. The length of one side of the light-receiving part of pixel 21 is, for example, 6 μm. Pixel 21 has higher sensitivity compared to, for example, a PD (Photo Diode) pixel structure, and has a smaller light-receiving area compared to, for example, a SPAD (Single Photon Avalanche Diode) signal multiplication pixel structure.

[0046] Furthermore, the pixels 21 can perform continuous global shutter operation. Global shutter operation is an operation in which multiple pixels 21 are exposed at the same time and signal charge is read out. As a result, the multiple pixels 21 constituting the sensor 20 can simultaneously receive multiple photons emitted by each of the multiple atoms 201 constituting the atomic array 200. Furthermore, as a result, the multiple pixels 21 constituting the sensor 20 can repeatedly perform the operation of simultaneously receiving multiple photons.

[0047] Pixel 21 can perform exposure operations for a period shorter than the photon emission interval of antibunching. For example, if the photon-emitting atom is a rubidium atom, the photon emission interval is approximately 20 nsec. Pixel 21 performs exposure operations for, for example, an exposure period of 10 nsec.

[0048] The control unit 30 performs information processing to control the exposure of multiple pixels 21 for multiple exposure periods. For example, the control unit 30 divides at least two or more pixels 21 into multiple groups and controls each group to be exposed for a different exposure period. More specifically, the control unit 30 controls pixels 21 located in odd-numbered rows and pixels 21 located in even-numbered rows to be exposed for different exposure periods.

[0049] The evaluation unit 40 performs information processing to evaluate the unity of photons contained in light by comparing the detection results for multiple exposure periods. The evaluation unit 40 evaluates the unity of photons by comparing the outputs of multiple pixels 21 for each of the multiple exposure periods.

[0050] The control unit 30 and the evaluation unit 40 are implemented, for example, by a microcomputer. The control unit 30 and the evaluation unit 40 may also be implemented by a processor or dedicated circuitry. The functions of the control unit 30 and the evaluation unit 40 are realized by the execution of software, such as computer programs, by the hardware, such as the microcomputer or processor, that constitutes the control unit 30 and the evaluation unit 40.

[0051] The atom supply unit 210 supplies atoms 201 to be used as qubits in a cold atom quantum computer. The atoms 201 supplied by the atom supply unit 210 are, for example, rubidium atoms. Atoms 201 may also be ytterbium atoms.

[0052] The optical tweezers laser unit 220 irradiates the atoms 201 supplied by the atom supply unit 210 with an optical tweezers laser to arrange them in a two-dimensional array. For example, the optical tweezers laser unit 220 fixes the atoms 201 in place by irradiating the positions where the atoms 201 are to be placed with the optical tweezers laser from multiple directions.

[0053] The atomic array 200 is formed by arranging multiple atoms 201 in a two-dimensional array. The atomic array 200 is formed when multiple atoms 201 supplied by the atom supply unit 210 are fixed by an optical tweezers laser irradiated by the optical tweezers laser unit 220. For a cold atom quantum computer to operate, the atomic array 200 must be composed of single atoms.

[0054] The excitation laser unit 300 irradiates each of the multiple atoms 201 constituting the atomic array 200 with an excitation laser to cause them to emit photons. The excitation laser irradiated by the excitation laser unit 300 causes each of the multiple atoms 201 constituting the atomic array 200 to emit light and emit photons. The excitation laser is, for example, a pulsed laser. The pulse width of the pulsed laser used as the excitation laser may be 20 nsec or 300 msec, and the excitation laser may be continuous light.

[0055] Synchrotron radiation L1 is light irradiated from an atomic array 200 to the sensor 20, consisting of multiple photons emitted by multiple atoms 201. In synchrotron radiation L1, it is possible to identify which atom 201 emitted each of the multiple photons.

[0056] The optical system 100 controls the distribution of light irradiated from the atomic array 200 to the sensor 20. When an atom 201 is irradiated with an excitation laser, it emits photons in all directions. In other words, the light emitted from each of the atoms 201 constituting the atomic array 200 spreads out in a spherical shape centered on the atom 201. The optical system 100 guides the photons emitted by the multiple atoms 201 constituting the atomic array 200 so that they are received by the pixels 21. More specifically, the optical system 100 is formed so that each of the multiple photons emitted by the multiple atoms 201 constituting the atomic array 200 is received across multiple pixels 21. The optical system 100 is realized, for example, by lenses.

[0057] [The process of setting up a cold atom quantum computer] Next, the operation of setting up a cold-atom quantum computer will be described. The observation and evaluation system 10 according to the embodiment is a system for confirming whether or not the atomic array 200 is composed of single atoms during the setup of a cold-atom quantum computer. Figure 5 is a flowchart illustrating the overall operation, including the observation and evaluation system according to the embodiment.

[0058] First, the atom supply unit 210 supplies Rb atoms 201 (S11 in Figure 5). Specifically, the atom supply unit 210 supplies multiple Rb atoms 201 into the space forming the atom array 200.

[0059] Next, the optical tweezers laser unit 220 traps the Rb atoms 201 by irradiating them with the optical tweezers laser (S12 in Figure 5). Specifically, the optical tweezers laser unit 220 irradiates the atomic array 200 with the optical tweezers laser to position the Rb atoms 201 at the positions where they should be placed.

[0060] Next, the excitation laser unit 300 excites the Rb atoms 201 by irradiating them with the excitation laser (S13 in Figure 5). Specifically, the excitation laser unit 300 irradiates the excitation laser at the positions in the atomic array 200 where the Rb atoms 201 should be located.

[0061] The excited Rb atom 201 emits a photon. The observation and evaluation system 10 simultaneously observes the photons emitted by each of the multiple Rb atoms 201 constituting the atomic array 200 and evaluates the singularity of each of the multiple photons observed simultaneously (S14 in Figure 5). If the evaluation of the singularity of the photons determines that it is in a single-photon state, it can be confirmed that the Rb atom 201 that emitted the photon is a single atom. The observation and evaluation system 10 determines whether each of the multiple Rb atoms 201 constituting the atomic array 200 is a single atom or not. In this way, the observation and evaluation system 10 determines whether the atomic array 200 is composed of single atoms or not. The process performed in step S14 will be described in detail later.

[0062] If it is determined that the system is in a single-photon state (Yes in S15 of Figure 5), that is, if it is determined that the atomic array 200 is composed of single atoms, the process proceeds to step S16.

[0063] If it is determined that the system is not in a single-photon state (No in S15 of Figure 5), that is, if it is determined that the atomic array 200 is not composed of single atoms, the process returns to step S11. In the operation of setting up the cold atom quantum computer, the processes of steps S11 to S15 are repeated until the observation and evaluation system 10 determines that the system is in a single-photon state.

[0064] Next, in the cold atom quantum computer, the quantum entanglement state of each Rb atom 201 constituting the atomic array 200 is evaluated (S16 in Figure 5). If it is determined that the atoms are quantum entangled (Yes in S17 in Figure 5), the process proceeds to step S18. If it is determined that the atoms are not quantum entangled (No in S17 in Figure 5), the process returns to step S11. In the operation of setting up the cold atom quantum computer, the processes from steps S11 to S17 are repeated until it is determined that the atoms are quantum entangled.

[0065] Finally, the quantum computer is executed (S18 in Figure 5). The setup of the cold atom quantum computer is completed, and the quantum computer is allowed to perform the desired computational processing.

[0066] The determination in steps S15 and S17 may be performed on all Rb atoms 201 constituting the atomic array 200, or it may be performed on each of the multiple Rb atoms constituting the atomic array 200.

[0067] Following these steps, it is possible to set up and operate a cold-atom quantum computer.

[0068] [Operation to evaluate photon unity] Next, the operation of the observation and evaluation system 10 will be described. In other words, the process of step S14 in Figure 5 will be explained in detail. Figure 6 is a flowchart illustrating the operation of the observation and evaluation system 10 according to the embodiment.

[0069] First, in step S13 of Figure 5, the excitation laser unit 300 irradiates the Rb atom 201 with the excitation laser to excite the Rb atom 201, and the excited Rb atom 201 emits photons.

[0070] Pixel 21 exposes the light emitted by Rb atoms 201 over two exposure periods (S21 in Figure 6). Sensor 20 uses multiple pixels 21 to simultaneously expose the photons emitted by each of the multiple Rb atoms 201 constituting the atomic array 200. Control unit 30 controls the multiple pixels 21 constituting sensor 20 to be exposed over two exposure periods. At this time, control unit 30 divides the multiple pixels 21 into two groups and controls each group to be exposed over different exposure periods.

[0071] More specifically, the sensor 20 is positioned such that the light emitted by each of the multiple atoms 201 constituting the atomic array 200 is exposed across at least two of the multiple pixels 21. The control unit 30 divides the multiple pixels 21 into two groups and controls them to be exposed for different exposure periods for each group.

[0072] For example, the sensor 20 is positioned such that the light emitted by each of the multiple atoms 201 constituting the atomic array 200 is exposed across pixels 21 located in odd-numbered rows and pixels 21 located in even-numbered rows. The control unit 30 controls the exposure of pixels 21 located in odd-numbered rows and pixels 21 located in even-numbered rows with different exposure periods. Figure 7 is a diagram illustrating multiple groups of pixels 21 according to this embodiment.

[0073] In Figure 7, the circles indicated by dots represent regions in the sensor 20 that photons can reach. In other words, among the multiple pixels 21 that make up the sensor 20, the pixels 21 on which the circles are superimposed can receive photons emitted by the atoms 201 that make up the atomic array 200.

[0074] In Figure 7, the sensor 20 is arranged so that one photon is received by one of the four pixels 21 arranged in a 2x2 grid. The control unit 30 divides the pixels 21 arranged in even rows into one group and the pixels 21 arranged in odd rows into another group, and controls the exposure to be performed with different exposure periods for each group.

[0075] Note that the grouping of pixels 21 does not have to be limited to two groups: pixels 21 arranged in even rows and pixels 21 arranged in odd rows. The sensor 20 is positioned such that each of the multiple photons emitted by each of the multiple atoms 201 is exposed across at least two of the multiple pixels 21. As long as these at least two pixels 21 are distributed into at least two groups, the grouping of pixels is not particularly limited.

[0076] The control unit 30 controls the exposure to occur at different timings for each of the two groups into which the multiple pixels 21 are separated. Figure 8 is a diagram illustrating the timing of multiple exposure periods according to this embodiment.

[0077] In Figure 8, the horizontal axis represents time t. The upper part of the horizontal axis in Figure 8 shows how photons in an antibunching state reach sensor 20. Each of the dots represents a photon, and the dashed line shows the probability distribution of photon existence. The probability distribution of photons is a distribution that shows the probability of when a photon reaches sensor 20. The probability distribution of a single photon is an upward-convex curve, with the highest probability of the photon's existence at the peak. The probability distribution of photons follows, for example, a binomial distribution. Since the photon emission interval of Rb atom 201 is approximately 20 nsec, the period between peaks in the photon probability distribution is approximately 20 nsec.

[0078] In Figure 8, the timing of the exposure period is shown on the lower side of the horizontal axis. As shown in Figure 8, the control unit 30 controls the pixels 21 located in even-numbered rows to be exposed during the first exposure period tC, and controls the pixels 21 located in odd-numbered rows to be exposed during the second exposure period tD.

[0079] As shown in Figure 8, the exposure widths for the first exposure period tC and the second exposure period tD are the same. The exposure width is the length of time for which pixel 21 is exposed. The exposure widths for the first exposure period tC and the second exposure period tD are, for example, 10 nsec, but may also be 3 nsec or 5 nsec. The exposure widths for the first exposure period tC and the second exposure period tD are not particularly limited as long as they are shorter than the photon emission interval of atom 201.

[0080] When a pixel 21 is exposed, the control unit 30 compares the output of the pixel 21 during the two exposure periods (S22 in Figure 6). Specifically, the evaluation unit 40 compares the output of the pixels 21 located in even rows during the first exposure period tC with the output of the pixels 21 located in odd rows during the second exposure period tD. Figure 9 is a diagram illustrating how photons are exposed during multiple exposure periods according to this embodiment.

[0081] In Figure 9, each of the dots represents a photon, and the downward arrows extending from the circles indicate the timing of the photon's arrival at the sensor 20. As shown in Figure 9, there are four possible combinations of the output of a pixel 21 exposed during the first exposure period tC and the output of a pixel 21 exposed during the second exposure period tD. In each pattern, the combination of pixel 21 outputs is shown in the format (output of pixel 21 exposed during the first exposure period tC, output of pixel 21 exposed during the second exposure period tD). Here, the combination of pixel 21 outputs refers to the combination of outputs of multiple pixels 21 that expose the emission of the same atom 201.

[0082] When a photon is exposed by pixel 21, the charge is multiplied by pixel 21, and the sensor output becomes High. In this way, the output of pixel 21 when the sensor output is High is represented as "1".

[0083] If no photons are exposed by pixel 21, the sensor output remains Low. Thus, the output of pixel 21 when the sensor output is Low is represented as "0".

[0084] Pattern A is the case where the timing at which the photon reaches the sensor 20 is neither the first exposure period tC nor the second exposure period tD. In the case of Pattern A, the output combination of pixel 21 is (0, 0). Pattern B is the case where the timing at which the photon reaches the sensor 20 is the first exposure period tC but not the second exposure period tD. In the case of Pattern B, the output combination of pixel 21 is (0, 1). Pattern C is the case where the timing at which the photon reaches the sensor 20 is not the first exposure period tC but is the second exposure period tD. In the case of Pattern C, the output combination of pixel 21 is (1, 0). Pattern D is the case where the timing at which the photon reaches the sensor 20 is both the first exposure period tC and the second exposure period tD. In the case of Pattern D, the output combination of pixel 21 is (1, 1).

[0085] As shown in Figure 8, for example, when there is no common period between the first exposure period tC and the second exposure period tD, the combination of outputs of pixel 21 can take the forms of patterns A, B, and C.

[0086] As shown in the k-th frame in Figure 8, when the first exposure period tC and the second exposure period tD are at the same timing, the output combinations of pixel 21 can take the forms of pattern A and pattern D.

[0087] If there is a period common to both the first exposure period tC and the second exposure period tD, the output combination of pixel 21 can take on all patterns: pattern A, pattern B, pattern C, and pattern D.

[0088] Next, the control unit 30 determines whether or not N frames have been exposed (S23 in Figure 6). The control unit 30 controls the exposure of the pixels 21 in multiple frames. In one frame, the control unit 30 divides the multiple pixels 21 into two groups and controls the pixels 21 to be exposed for different exposure periods (i.e., a first exposure period tC and a second exposure period tD) for each group. In each of the multiple frames, the timing of the second exposure period tD is different from the timing of the first exposure period tC.

[0089] The number of frames N is the number of divisions of the exposure timing. The number of divisions of the exposure timing is the number of timings for the second exposure period tD relative to the timing of the first exposure period tC. In other words, there are N possible timings for the second exposure period tD relative to the timing of the first exposure period tC in a given frame. The number of frames N is set in advance by the user. For example, the number of frames N is 100, but it could also be 30 or 300. The number of frames N is not particularly limited as long as it is a sufficient number to evaluate the unity of photons.

[0090] Here, as shown in Figure 8, if the sensor 20 can perform continuous exposure, the length of one frame will be equal to the emission exposure interval of the atoms 201, for example, 20 nsec.

[0091] If it is determined that N frames have not yet been exposed (No in S23 of Figure 6), the control unit 30 changes the timing of the two exposure periods within the frame (S24 in Figure 6). Specifically, the control unit 30 changes the timing of the second exposure period tD relative to the timing of the first exposure period tC within the frame.

[0092] For example, the control unit 30 fixes the timing of the first exposure period tC within the frame and changes the timing of the second exposure period tD within the frame to scan the frame.

[0093] As shown in Figure 8, the timing of the first exposure period tC within the frame is fixed so that the peak position of the photon probability distribution falls within the first exposure period tC. In other words, the timing of the first exposure period tC is fixed so that the pixel 21 is exposed during the period within the frame when the probability of a photon reaching the sensor 20 is highest.

[0094] Furthermore, as shown in Figure 8, the timing of the second exposure period tD within the frame has been modified to scan within the frame.

[0095] For example, in the first frame, the timing at which the second exposure period tD begins is set to the timing at which the first frame begins. In the second frame, the timing at which the second exposure period tD begins is set to be delayed by a predetermined amount of time from the timing at which the second frame begins. In this way, the control unit 30 can change the timing of the second exposure period tD to scan within a frame by shifting the timing at which the second exposure period tD begins within a frame by a predetermined amount of time. The predetermined time is determined by the length of the frame and the number of frames N. In the k-th frame, the first exposure period tC and the second exposure period tD are set to be at the same timing, and in the nth frame, the timing at which the second exposure period tD ends is set to be at the timing at which the nth frame ends.

[0096] When the control unit 30 changes the timing of the two exposure periods within a frame, the process returns to S21, and the pixel 21 exposes the Rb atoms 201 to light emission during the two exposure periods with changed timing. In each frame, the pixel 21 may be exposed multiple times.

[0097] If it is determined that N frames of exposure have been performed (Yes in S23 of Figure 6), the evaluation unit 40 generates a graph (S25 of Figure 6). Specifically, the evaluation unit 40 generates a graph for evaluating the single-photon state based on the output results of the obtained pixels.

[0098] For example, the evaluation unit 40 generates a graph where the horizontal axis represents the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD, and the vertical axis represents the probability of output (1, 0) or (0, 1) occurring. In other words, it generates a graph showing the probability of pattern B or pattern C, as shown in Figure 9, occurring in each of multiple frames.

[0099] Once the graph is generated, the evaluation unit 40 compares the shape of the generated graph with the shape of the graph in the case of a single-photon state (S26 in Figure 6).

[0100] For example, in the case of a single-photon state, the shape of a graph with the horizontal axis representing the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD, and the vertical axis representing the probability of output (1, 0) or (0, 1) occurring, will have a single downward-convex peak. More specifically, the shape of the graph will have a downward-convex peak only at the position where the probability of the photon's existence is highest. The shape of the graph in the case of a single-photon state will be described in more detail later.

[0101] If the shapes are determined to match (Yes in S27 of Figure 6), the evaluation unit 40 evaluates it as a single-photon state (S28 of Figure 6). In other words, for example, if in step S25 of Figure 6 a graph is generated with the horizontal axis representing the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD, and the vertical axis representing the probability of output (1, 0) or (0, 1) occurring, the evaluation unit 40 evaluates it as a single-photon state if the shape of the graph has a downward-convex peak only at the position where the probability of photon existence is highest.

[0102] If the shape is determined not to match (No in S27 of Figure 6), the evaluation unit 40 evaluates that it is not a single-photon state (S29 of Figure 6).

[0103] With this operation, the observation and evaluation system 10 can determine whether each of the multiple atoms 201 constituting the atomic array 200 is a single atom by simultaneously observing the photons emitted by each of the multiple atoms 201 constituting the atomic array 200 using the sensor 20, and by evaluating the singularity of each of the multiple photons observed simultaneously. Therefore, with this operation, the observation and evaluation system 10 can more easily determine whether each of the multiple atoms constituting the atomic array is a single atom.

[0104] [Graph Shape] Here, we will explain the shape of the graph used in step S26 of Figure 6, in the case of a single-photon state.

[0105] First, let's consider the schematic probability of a single photon reaching sensor 20. The schematic probability of a photon reaching sensor 20 follows a binomial distribution.

[0106] Next, we will explain the shape of the graph when the sensor 20 is in a single-photon state, given that the photon reaches the sensor 20 with a probability that follows a binomial distribution. In other words, we will explain the shape of the graph when the sensor is in a single-photon state, as used in step S26 of Figure 6. Figure 10 is a graph showing the probability that the output combination when exposed during the period in which a single photon arrives according to the embodiment is (0, 1) or (1, 0).

[0107] Figure 10 shows a graph illustrating the probability of exposure occurring during either the first exposure period tC or the second exposure period tD. In the graph shown in Figure 10, the horizontal axis represents the frame number, i.e., the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD. Moving in the positive direction of the horizontal axis indicates that the timing of the second exposure period tD is later than the timing of the first exposure period tC. The vertical axis represents the probability that the output combination of pixel 21 is (0, 1) or (1, 0). Figure 10 shows the graph when the number of frames N is 100.

[0108] Figure 10(a) is a graph showing the probability that the output combination when exposed during the period in which a single photon arrives is (0, 1) or (1, 0), given that the timing of the first exposure period tC coincides with the peak of the photon's probability of existence. Specifically, the graph shows the case where the timing of the first exposure period tC is set to coincide with the timing of the 50th period. The shape of the graph shown in Figure 10(a) has one downward-convex peak. In the graph shown in Figure 10(a), the probability that the output combination of pixel 21 is (0, 1) or (1, 0) is lowest in frames where the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD is 0, and this probability is approximately 0.073.

[0109] Figure 10(b) is a graph showing the probability that the output combination when exposed during the period in which a single photon arrives is (0, 1) or (1, 0), when the timing of the first exposure period tC and the peak of the photon's probability of existence are slightly out of sync. Specifically, the graph shows the case where the timing of the first exposure period tC is set to coincide with the 40th period, and is set to be 10 periods out of sync with the peak of the photon's probability of existence. The shape of the graph shown in Figure 10(b) has one downward-convex peak. In the graph shown in Figure 10(b), the probability that the output combination of pixel 21 is (0, 1) or (1, 0) is lowest in a frame where the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD is 10 periods, and this probability is approximately 0.010.

[0110] Figure 10(c) is a graph showing the probability that the output combination when exposed during the period in which a single photon arrives is (0, 1) or (1, 0) when the timing of the first exposure period tC is significantly out of sync with the peak of the photon's probability of existence. Specifically, the graph shows the case where the timing of the first exposure period tC is set to coincide with the 30th period, which is 20 periods out of sync with the peak of the photon's probability of existence. The shape of the graph shown in Figure 10(c) has a single downward-convex peak. In the graph shown in Figure 10(c), the probability that the output combination of pixel 21 is (0, 1) or (1, 0) is lowest in a frame where the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD is 20 periods, and this probability is approximately 0.0000215.

[0111] As shown in Figure 10, in the case of a single-photon state, the shape of the graph showing the probability that the output combination of pixel 21 is (0, 1) or (1, 0) has a single downward-convex peak. Therefore, the evaluation unit 40 can evaluate the singleness of the photon based on whether or not the shape of the graph generated in step S25 of Figure 7 has a single downward-convex peak.

[0112] Furthermore, as shown in Figure 10, even when the first exposure period tC is set so as not to include the peak of the photon probability of existence, the shape of the graph will have one downward-convex peak. Here, the larger the time difference between the timing of the first exposure period tC and the timing of the peak of the photon probability of existence, the smaller the downward-convex change becomes, so it is necessary to adjust the range when evaluating.

[0113] Next, we will describe the shape of the graph generated when the state is not single-photon. In other words, we will describe the shape of the graph generated based on the output of the pixel 21 that can expose the photons emitted by the atoms 201 when an atom 201 is not present in the position where one atom 201 should be, or when two or more atoms 201 are present in that position.

[0114] Figure 11 is a graph showing the probability that the output combination when exposed during the period when two photons arrive according to the embodiment will be (0, 1) or (1, 0). In the graph shown in Figure 11, the horizontal axis represents the frame number, and the vertical axis represents the probability that the output combination of pixel 21 will be (0, 1) or (1, 0). In the graph shown in Figure 11, the number of frames N is 30. As shown in Figure 11, the shape of the graph has two downward-convex peaks.

[0115] Furthermore, if no photons reach the target, in other words, if atom 201 of the atomic array 200 is not present at the expected position, the output is zero and a constant graph is obtained. In other words, the shape of the graph does not have a downward-convex peak.

[0116] Based on the above, the evaluation unit 40 can evaluate the unity of photons by determining whether or not the shape of the graph has a single downward-convex peak.

[0117] In the above embodiment, the unity of photons was evaluated using a graph in which the horizontal axis represents the time difference between the timing of the first exposure period tC and the timing of the second exposure period tD, and the vertical axis represents the probability of output (1, 0) or (0, 1) occurring. However, the evaluation method is not limited to this. The evaluation unit 40 can evaluate the unity of photons by evaluating the characteristics that appear when a single-photon state is present.

[0118] [Effects, etc.] The technologies derived from the disclosures in this specification include, for example, the following. The technologies derived from the disclosures in this specification will be described below, along with the effects obtained by such technologies.

[0119] Technology 1 is an observation and evaluation system 10 for evaluating the unity of photons in order to determine whether or not multiple atoms 201 are arranged in a two-dimensional array, comprising: a sensor 20 in which multiple pixels 21 having a multiplication function are arranged in a two-dimensional array and expose the light emitted by multiple atoms 201 all at once; a control unit 30 that controls the multiple pixels 21 to be exposed for multiple exposure periods; and an evaluation unit 40 that evaluates the unity of photons contained in the light by comparing the detection results for multiple exposure periods.

[0120] Such an observation and evaluation system 10 can determine whether each of the multiple atoms 201 constituting the atomic array 200 is a single atom by simultaneously observing the photons emitted by each of the multiple atoms 201 constituting the atomic array 200 using a sensor 20, and by evaluating the singularity of each of the multiple photons observed simultaneously. Therefore, such an observation and evaluation system 10 can more easily determine whether each of the multiple atoms 201 constituting the atomic array 200 is a single atom.

[0121] Technology 2 is an observation and evaluation system 10 of Technology 1, in which the sensor 20 is arranged such that each of the lights emitted by each of the multiple atoms 201 is exposed across at least two or more of the multiple pixels 21, and the control unit 30 divides at least two or more pixels 21 into multiple groups and controls the exposure to each of the multiple groups with a different exposure period.

[0122] Such an observation and evaluation system 10 can evaluate the unity of photons based on exposure results obtained by exposing each of a single atom 201 to light using at least two pixels 21 and exposing the at least two pixels 21 for exposure periods at different timings.

[0123] Technology 3 is an observation and evaluation system 10 of Technology 1, in which the sensor 20 is arranged such that the light emitted by each of the multiple atoms 201 is exposed across pixels 21 arranged in odd rows and pixels 21 arranged in even rows of the multiple pixels 21, and the control unit 30 controls the exposure of the pixels 21 arranged in odd rows and pixels 21 arranged in even rows with different exposure periods.

[0124] Such an observation and evaluation system 10 can evaluate the unity of photons based on exposure results obtained by exposing the light emitted by each of the atoms 201 using pixels 21 arranged in odd rows and pixels 21 arranged in even rows, and exposing the pixels 21 for each of the two groups with different exposure periods at different timings.

[0125] Technology 4 is an observation and evaluation system 10 of any of Technologies 1 to 3, in which the evaluation unit 40 evaluates the unity of photons by comparing the outputs of multiple pixels 21 in each of multiple exposure periods.

[0126] Such an observation and evaluation system 10 can evaluate the unity of a photon by comparing a combination of outputs from multiple pixels 21 with a combination of outputs that would be observed in a single-photon state.

[0127] Technology 5 is the observation and evaluation system 10 of Technology 4, in which multiple exposure periods include periods that overlap with each other.

[0128] Such an observation and evaluation system 10 can obtain output combinations even when multiple pixels 21 are exposed at the same time.

[0129] Technology 6 is an observation and evaluation system 10 of any of Technologies 1 to 5, wherein the multiple exposure periods include a first exposure period tC and a second exposure period tD, and the control unit 30 controls the exposure of pixels 21 in multiple frames, and in each of the multiple frames, the timing of the second exposure period tD is different from the timing of the first exposure period tC.

[0130] Such an observation and evaluation system 10 can generate the output results for each pixel in each frame based on the results of exposures performed with different timings for exposure periods in multiple frames.

[0131] Technology 7 is an observation and evaluation system 10 of Technology 6, in which the length of the first exposure period tC and the length of the second exposure period tD are the same, and the control unit 30 exposes the pixels 21 in multiple frames, with the timing of the first exposure period tC fixed in each of the multiple frames and the timing of the second exposure period tD varying to scan the frames.

[0132] Such an observation and evaluation system 10 can generate pixel output results for each frame more efficiently by scanning within the frame.

[0133] Technology 8 is an observation and evaluation method for evaluating the unity of photons in order to determine whether a plurality of atoms 201 executed by a computer are arranged in a two-dimensional array, and includes a control step of controlling a plurality of exposure periods for detecting light emitted by a plurality of atoms 201, a detection step of detecting light by exposing a plurality of pixels 21 having a multiplication function arranged in a two-dimensional array for a plurality of exposure periods, and an evaluation step of evaluating the unity of photons contained in the light by comparing the detection results for the plurality of exposure periods.

[0134] This observation and evaluation method makes it easier to determine whether each of the multiple atoms 201 constituting the atomic array 200 is a single atom or not.

[0135] Technique 9 is a program that causes a computer to execute the observation and evaluation method of Technique 8.

[0136] Such a program can help make it easier to determine whether each of the multiple atoms 201 constituting the atomic array 200 is a single atom or not.

[0137] (Other embodiments) Although embodiments have been described above, this disclosure is not limited to the embodiments described above.

[0138] For example, in the above embodiment, the observation and evaluation system was implemented by a single device, but the observation and evaluation system may be implemented by multiple devices. When the observation and evaluation system is implemented by multiple devices, the components of the observation and evaluation system (in particular, the functional components) may be distributed among the multiple devices in any way.

[0139] Furthermore, the method of communication between devices in the above embodiment is not particularly limited. In addition, relay devices (such as gateway devices), which are not shown, may be involved in the communication between devices.

[0140] Furthermore, in the above embodiment, a process executed by a specific processing unit may be executed by another processing unit. Also, the order of multiple processes may be changed, or multiple processes may be executed in parallel.

[0141] Furthermore, in the above embodiment, each component may be realized by executing a software program suitable for each component. Each component may also be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0142] Furthermore, each component may be implemented by hardware. For example, each component may be a circuit (or integrated circuit). These circuits may form a single circuit as a whole, or they may be separate circuits. Also, each of these circuits may be a general-purpose circuit or a dedicated circuit.

[0143] Furthermore, the general or specific embodiments of this disclosure may be implemented as a system, apparatus, method, integrated circuit, computer program, or recording medium such as a computer-readable CD-ROM. They may also be implemented in any combination of systems, apparatus, methods, integrated circuits, computer programs, and recording media.

[0144] For example, this disclosure may be implemented as an observation and evaluation method of the above embodiment, or as an observation and evaluation method executed by a computer such as an observation and evaluation system (observation and evaluation device) of the above embodiment, or as a program (in other words, a computer program product) for causing a computer to execute the observation and evaluation method. Furthermore, this disclosure may be implemented as a computer-readable non-temporary recording medium on which such a program is recorded.

[0145] Furthermore, this disclosure also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art could conceive, or forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of this disclosure. [Industrial applicability]

[0146] This disclosure can be used in a device for performing the initial setup of a cold atom quantum computer. [Explanation of symbols]

[0147] 10. Observation and Evaluation System 20 sensors 21 pixels 30 Control Unit 40 Evaluation Department 100 Optical system 200 Atomic Array 201 atom (Rb atom) 210 Atomic Supply Department 220 Laser section for optical tweezers 300 Excitation laser section L1 synchrotron radiation tC 1st exposure period tD Second exposure period

Claims

1. An observation and evaluation system that evaluates the unity of photons in order to determine whether or not multiple atoms are arranged in a two-dimensional array, A sensor comprising multiple pixels arranged in a two-dimensional array, each having a multiplication function that simultaneously exposes the light emitted by the aforementioned multiple atoms, A control unit that controls the exposure of the plurality of pixels for a plurality of exposure periods, The system includes an evaluation unit that evaluates the unity of photons contained in the light by comparing the detection results over the aforementioned multiple exposure periods. Observation and evaluation system.

2. The sensor is arranged such that the light emitted by each of the plurality of atoms is exposed across at least two or more pixels among the plurality of pixels. The control unit divides the at least two pixels into a plurality of groups and controls the exposure of each of the plurality of groups with a different exposure period. The observation and evaluation system according to claim 1.

3. The sensor is arranged such that the light emitted by each of the plurality of atoms is exposed across pixels located in odd-numbered rows and pixels located in even-numbered rows of the plurality of pixels. The control unit controls the exposure of pixels located in odd-numbered rows and pixels located in even-numbered rows with different exposure periods. The observation and evaluation system according to claim 1.

4. The evaluation unit evaluates the unity of the photons by comparing the output of the plurality of pixels during each of the plurality of exposure periods. An observation and evaluation system according to any one of claims 1 to 3.

5. The plurality of exposure periods include periods that overlap with each other. The observation and evaluation system according to claim 4.

6. The plurality of exposure periods include a first exposure period and a second exposure period. The control unit controls the exposure of the pixels in multiple frames, Each of the aforementioned plurality of frames has a second exposure period timing that is different from the first exposure period timing. An observation and evaluation system according to any one of claims 1 to 3.

7. The length of the first exposure period and the length of the second exposure period are the same. The control unit exposes the pixels in the plurality of frames, such that the timing of the first exposure period in each of the plurality of frames is fixed, and the timing of the second exposure period is varied so as to scan the frames. The observation and evaluation system according to claim 6.

8. An observational evaluation method for evaluating the unity of photons in order to determine whether or not multiple atoms are arranged in a two-dimensional array, which is performed by a computer, A control step for controlling multiple exposure periods for detecting light emitted by the multiple atoms, A detection step in which light is detected by exposing a plurality of pixels having a multiplication function arranged in a two-dimensional array to the plurality of exposure periods, The evaluation step includes evaluating the unity of photons contained in the light by comparing the detection results over the multiple exposure periods, Observation and evaluation methods.

9. A program for causing a computer to execute the observation and evaluation method described in claim 8.

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