Measuring device, measuring method, and program

Abstract

This measuring device comprises: a plurality of measuring units (5a to 5c) that measure an operation value in accordance with an operation time; and delay units (4b, 4c) that delay an operation start time of each of the measuring units (5a to 5c) that operate after one of the measurement units, such that the operation of said one measurement unit starts at an input time of a synchronization signal and the operation of the next measurement unit starts when the operation value of the one measurement unit reaches a predetermined threshold (Vth). Each of the measurement units (5a to 5c) starts operating at an operation start time and stops operating when the operation value reaches the threshold or when a photon detection signal is input. Furthermore, the measuring device is provided with a control unit (7) which, when the photon detection signal is input, calculates a photon arrival time on the basis of the total value of the operation value of the measurement unit that is operating and the operation values of the measurement units that have finished operating.

Description

Measurement device, measurement method, and program

[0001] The present disclosure relates to a measurement device, a measurement method, and a program for measuring photon arrival times.

[0002] In order to achieve highly confidential communications, for example, Non-Patent Documents 1 and 2 propose a communication system using quantum key distribution (QKD) in which both the transmitter and receiver share a secret key that is difficult for others to eavesdrop on.

[0003] In QKD, the time elapsed from when a frame synchronization signal transmitted from a transmitter is received by a receiver until a photon (quantum) is detected (hereinafter referred to as "photon arrival time") is measured. As a method for measuring the photon arrival time, Non-Patent Documents 3 and 4 disclose time-correlated single photon counting (TC-SPC). As TC-SPC, a TAC-ADC method and a count-type TDC method have been proposed.

[0004] In the TAC-ADC method, current is passed from a current source to a capacitor when a synchronization signal is generated, increasing the capacitor voltage, and when a photon detection signal is detected, the current supply from the current source to the capacitor is stopped.The capacitor voltage at that time is measured, and the time from the generation of the synchronization signal to the acquisition of the photon detection signal (photon arrival time) is calculated based on this capacitor voltage.The TAC-ADC method has the advantage of being able to suppress jitter.

[0005] Furthermore, Non-Patent Document 5 discloses that an integrator is used to measure the photon arrival time in the TAC-ADC method. In addition to quantum communication, TC-SPC is also used in fluorescence / phosphorescence lifetime measurements and laser scanning microscopes.

[0006] Hiroki Takesueet al. "Quantum key distribution over a 40-dBchannel loss using superconducting single-photon detectors." Nature photonics 1.6 (2007): 343-348. Masahide Sasakiet al. "Field test of quantum key distribution in the TokyoQKD Network." Opticsexpress 19.11 (2011):10387-10409.Wolfgang Becker “The bh TCSPC Handbook”, EighthEditionWilliam R. Leo “Techniques for Nuclear and Particle PhysicsExperiments A How-toApproach”SecondRevised Edition, Springer-Verlag Berlin Heidelberg New York in 1994.Zule Xu et al. “Picosecond Resolution Time-to-Digital Converter Using Gm-C Integrator and SAR-ADC”

[0007] However, the TAC-ADC methods disclosed in Non-Patent Documents 3 and 4 have the problem that if the time between the input of a synchronization signal and the input of a photon detection signal is long, the voltage charged to the capacitor increases, resulting in increased power consumption. Furthermore, the voltage charged to the capacitor must then be discharged, requiring a discharge period. If the next synchronization signal is input during the discharge period, charging of the capacitor cannot begin. This makes it difficult to measure the photon arrival time. The count-type TDC method can measure for a longer period of time than the TAC-ADC method, but this requires a high-performance semiconductor chip.

[0008] Furthermore, the technique disclosed in Non-Patent Document 5 has a problem in that the calculation speed and the operating frequency are inversely proportional, so that the usable frequency is limited.

[0009] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a measurement device, a measurement method, and a program that are capable of measuring photon arrival times over a long period of time without being affected by available frequencies.

[0010] A measurement device of one aspect of the present disclosure is a measurement device that measures a photon arrival time from the input time of a synchronization signal to the input time of a photon detection signal, and includes a first input unit that inputs the synchronization signal, a second input unit that inputs the photon detection signal, a plurality of measurement units that measure operating values ​​according to operating time, and a delay unit that delays the operation start time of a measurement unit that operates after one measurement unit so that operation of one measurement unit starts at the input time of the synchronization signal and operation of the next measurement unit starts when the operating value of the one measurement unit reaches a predetermined threshold, each measurement unit starts operation at the operation start time and stops operation when the operating value reaches the threshold or when the photon detection signal is input, and further includes a control unit that calculates the photon arrival time based on the sum of the operating values ​​of the measurement units that are operating and the operating values ​​of the measurement units that have finished operating when the photon detection signal is input.

[0011] A measurement method according to one aspect of the present disclosure is a measurement method for measuring a photon arrival time from the input time of a synchronization signal to the input time of a photon detection signal, in which, at the input time of the synchronization signal, one of a plurality of measurement units that measure operating values ​​according to operating time starts operating, and when the operating value of the one measurement unit reaches a predetermined threshold, the operation of each measurement unit is executed so as to start operating the next measurement unit, and when the photon detection signal is input, the operation of the measurement unit currently operating is stopped, and the photon arrival time is calculated based on the sum of the operating values ​​of the measurement unit currently operating and the measurement unit that has completed its operation.

[0012] One aspect of the present disclosure is a program for causing a computer to function as the above-described measurement device.

[0013] According to the present disclosure, it is possible to measure photon arrival times over a long period of time, without being affected by available frequencies.

[0014] FIG. 1 is a block diagram showing the configuration of a measurement device according to a first embodiment. FIG. 2 is a timing chart showing the operation time periods of each measurement unit. FIG. 3 is a timing chart showing changes in the synchronization signal, detection signal, and charging voltage of each measurement unit. FIG. 4 is a circuit diagram of a timing circuit provided in each measurement unit. FIG. 5A is a first sub-diagram of a flowchart showing the processing procedure of the measurement device according to the first embodiment. FIG. 5B is a second sub-diagram of a flowchart showing the processing procedure of the measurement device according to the first embodiment. FIG. 6A is a circuit diagram of a timing circuit when there is one measurement unit. FIG. 6B is a circuit diagram of a timing circuit when there are n measurement units. FIG. 7 is a timing chart showing changes in the charging voltage of a capacitor when there is one measurement unit. FIG. 8 is a block diagram showing the configuration of a measurement device according to a second embodiment. FIG. 9 is a block diagram showing the configuration of a measurement device according to a third embodiment. FIG. 10 is a block diagram showing the configuration of a measurement device according to a fourth embodiment. FIG. 11A is a timing chart showing the synchronization signal, control signal, and charging voltage in the measurement device according to the fourth embodiment. Fig. 11B is a timing chart showing detection signals, control signals, and charging voltages in the measurement device according to the fourth embodiment Fig. 12 is a block diagram showing the hardware configuration of the embodiment.

[0015] [Description of First Embodiment] The following describes the embodiment with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a measurement device 100 according to the first embodiment. FIG. 2 is a timing chart showing the time periods during which each of the measurement units 5a to 5c (details will be described later) operates. FIG. 3 is a timing chart showing the changes in the synchronization signal s1, the detection signal s2, and the charging voltages V1 to V3 of each of the measurement units 5a to 5c. FIG. 4 is a circuit diagram of a timing circuit mounted in each of the measurement units 5a to 5c.

[0016] As shown in FIG. 1, the measurement device 100 includes a first input unit 1, a second input unit 2, a switch unit 3, delay units 4b and 4c, first to third measurement units 5a to 5c, ADC circuits 6a to 6c, and a control unit 7. Note that, in this embodiment, an example is described in which three measurement units 5a to 5c and three ADC circuits 6a to 6c are provided, but the present disclosure is not limited to this, and a configuration including two or four or more measurement units and ADC circuits is also possible. Note that, when the number of measurement units is n, the number of delay units is (n-1).

[0017] The measuring device 100 according to this embodiment measures the elapsed time (photon arrival time) from the synchronization signal s1 synchronized with the transmission time of a photon in a transmitter (not shown) that transmits a photon, until the photon detection signal s2 (hereinafter abbreviated as "detection signal s2") transmitted from the transmitter is detected by a detector (not shown).

[0018] The first input unit 1 receives a synchronization signal s1 synchronized with the transmission time of a photon in the transmitter unit.

[0019] The second input section 2 receives a detection signal s2 transmitted from the transmitter and detected by the detector.

[0020] The switch unit 3 switches the output destination of the detection signal s2 output from the second input unit 2 to one of the measurement units 5a to 5c based on a control command output from the control unit 7. Specifically, the control unit 7 switches the output destination of the detection signal s2 when a delay time (T1 and T2, described below) has elapsed, based on the time when the synchronization signal s1 is input to the first input unit 1. In other words, the switch unit 3 switches the output destination of the detection signal s2 to one of the multiple measurement units.

[0021] The delay unit 4b delays the synchronization signal s1 output from the first input unit 1 and outputs the delayed signal to the second measurement unit 5b. As shown in FIG. 2B, the delay time T1 in the delay unit 4b is set to the operating time of the first measurement unit 5a. The operating time corresponds to the time required for the charging voltage V1 to reach the threshold voltage Vth after charging of the first measurement unit 5a begins (t4 to t5 in FIG. 3C). The charging voltage is an example of an operating value.

[0022] The delay unit 4c delays the synchronization signal s1 output from the first input unit 1 and outputs the delayed signal to the third measurement unit 5c. As shown in FIG. 2C, the delay time T2 in the delay unit 4c is set to the total operating time of the first measurement unit 5a and the second measurement unit 5b. The total operating time corresponds to the sum of the time required for the charging voltage V1 to reach the threshold voltage Vth after the first measurement unit 5a starts charging and the time required for the charging voltage V2 to reach the threshold voltage Vth after the second measurement unit 5b starts charging (t9 to t11 in FIG. 3E).

[0023] That is, the delay units 4b and 4c set the charging start time (operation start time) of the measurement units (second and third measurement units 5b and 5c) that will charge (operate) after the first measurement unit 5a so that charging (operation of one measurement unit) of one measurement unit (first measurement unit 5a) starts at the input time of the synchronization signal s1, and then charging (operation) of the next measurement unit starts when the charging voltage (operation value) of the first measurement unit 5a reaches a predetermined threshold voltage Vth.

[0024] As shown in FIG. 4, each of the measuring units 5a to 5c includes a timer circuit CK in which a current source 51 and a capacitor 52 are connected in series.

[0025] The timing circuit CK of the first measuring unit 5a starts the current source 51 at the time when the synchronization signal s1 is input to the first input port 1, causing a current to flow through the capacitor 52. The timing circuit CK stops the current source 51 at the time when the detection signal s2 is input to the second input port 2, thereby terminating the charging of the capacitor 52, and then switches to discharging. Specifically, as shown in FIG. 3(c), charging starts when the synchronization signal s1 is input at time t1, and terminates when the detection signal s2 is input at time t2. Thereafter, discharging switches to complete discharging at time t3.

[0026] If the detection signal s2 is not input, the timer circuit CK of the first measurement unit 5a stops charging the capacitor 52 when the charging voltage V1 reaches the threshold voltage Vth, and then switches to discharging. Specifically, charging starts when the synchronization signal s1 is input at time t4 shown in Figure 3, and ends if the detection signal s2 is not input by time t5. Then, discharging switches to complete at time t7.

[0027] The threshold voltage Vth can be set to, for example, an upper limit voltage to which the capacitor 52 can be charged. The first measuring unit 5a shown in Fig. 1 outputs the voltage charged in the capacitor 52 to the ADC circuit 6a.

[0028] The timer circuit CK of the second measuring unit 5b starts the current source 51 at a time delayed by the delay time T1 set by the delay unit 4b after the synchronization signal s1 is input to the first input unit 1, and causes a current to flow through the capacitor 52. As described above, the delay time T1 may be set to the charging time of the first measuring unit 5a (t4 to t5 in FIG. 3(c)). The charging time is an example of the operating time.

[0029] The timer circuit CK of the second measurement unit 5b stops charging the capacitor 52 when the detection signal s2 is input to the second input unit 2, and then starts discharging. Specifically, as shown in Figure 3(d), charging starts when the delay time T1 has elapsed at time t5, and ends when the detection signal s2 is input at time t6. Thereafter, discharging starts, and the capacitor is completely discharged at time t8.

[0030] If the detection signal s2 is not input, the timer circuit CK of the second measurement unit 5b stops charging the capacitor 52 when the charging voltage V2 reaches the threshold voltage Vth, and then switches to discharging. Specifically, as shown in Figure 3(d), the synchronization signal s1 is input at time t9, charging begins when the delay time T1 has elapsed at time t10, and charging ends if the detection signal s2 is not input by time t11. Thereafter, discharging begins, and the capacitor is completely discharged at time t14. The second measurement unit 5b outputs the voltage charged in the capacitor 52 to the ADC circuit 6b.

[0031] The timer circuit CK of the third measuring unit 5c starts the current source 51 at a time delayed by the delay time T2 set by the delay unit 4c after the synchronization signal s1 is input to the first input unit 1, and causes a current to flow through the capacitor 52. As described above, the delay time T2 may be set to the sum of the charging time of the first measuring unit 5a and the charging time of the second measuring unit 5b (t9 to t11 in FIG. 3(e)).

[0032] The timer circuit CK of the third measurement unit 5c stops charging the capacitor 52 when the detection signal s2 is input to the second input unit 2, and then switches to discharging. Specifically, as shown in Figure 3(e), the synchronization signal s1 is input at time t9, charging starts at time t11 when the delay time T2 has elapsed, and charging ends when the detection signal s2 is input at time t12. Thereafter, the timer circuit CK switches to discharging, and is completely discharged at time t13.

[0033] If the detection signal s2 is not detected, the timer circuit CK of the third measurement unit 5c stops charging the capacitor 52 when the charging voltage V3 reaches the threshold voltage Vth, and then starts discharging. The third measurement unit 5c outputs the voltage charged in the capacitor 52 to the ADC circuit 6c.

[0034] That is, the measurement unit 5a starts charging when the synchronization signal s1 is input. The measurement units 5b and 5c start charging at the charging start times set by the delay units 4b and 4c. Each of the measurement units 5a to 5c operates to stop charging (operation) when the charging voltage (operating value) reaches the threshold voltage Vth or when the photon detection signal s2 is input. Each of the measurement units 5a to 5c has the function of measuring the operating value (measuring the charging voltage) according to the operating time (charging time).

[0035] Each ADC circuit 6a to 6c converts the voltage measured by each measurement unit 5a to 5c into a digital signal. Each ADC circuit 6a to 6c then converts the digitized voltage into time. That is, when current flows from current source 51, capacitor 52 of timing circuit CK shown in FIG. 4 experiences a monotonically increasing charging voltage over time. Therefore, it is possible to calculate the elapsed time based on the synchronization signal s1, based on the charging voltage of capacitor 52. Each ADC circuit 6a to 6c outputs the elapsed time data to control unit 7.

[0036] The control unit 7 controls the switch unit 3 so that the detection signal s2 input to the second input unit 2 is output to the measuring units 5a to 5c that are currently charging. Specifically, when the first measuring unit 5a is currently charging (t4 to t5 in FIG. 3C), the output of the switch unit 3 is switched to the first measuring unit 5a side. When the second measuring unit 5b is currently charging (t10 to t11 in FIG. 3D), the output of the switch unit 3 is switched to the second measuring unit 5b side. When the third measuring unit 5c is currently charging (t11 and thereafter in FIG. 3E), the output of the switch unit 3 is switched to the third measuring unit 5c side. Therefore, when the detection signal s2 is input, charging by the measuring unit that is currently charging can be immediately stopped.

[0037] Based on the elapsed time data output from each ADC circuit 6a to 6c, the control unit 7 calculates the elapsed time from when the synchronization signal s1 is input to the first input unit 1 to when the detection signal s2 is input to the second input unit 2, i.e., the photon arrival time. That is, when the photon detection signal s2 is input, the control unit 7 calculates the photon arrival time based on the sum of the charging voltage (operating value) of the measurement unit during charging (operation) and the charging voltage (operating value) of the measurement unit after charging (operation) has finished. The control unit 7 outputs the calculated photon arrival time to a downstream device.

[0038] Next, the processing procedure of the measurement device 100 according to the first embodiment will be described with reference to the flowcharts shown in Figures 5A and 5B. First, in step S11 of Figure 5A, when a synchronization signal s1 is input, the first input unit 1 outputs the synchronization signal s1 to the first measurement unit 5a and the delay units 4b and 4c.

[0039] In step S12, the first measuring unit 5a activates the current source 51 of the timer circuit CK shown in Fig. 4 to start charging the capacitor 52. At this time, the control unit 7 controls the switch unit 3 so that the output destination is the first measuring unit 5a.

[0040] In step S13, the first measuring unit 5a determines whether or not the detection signal s2 has been input. If the detection signal s2 has been input (S13; YES), the process proceeds to step S14; if not (S13; NO), the process proceeds to step S17.

[0041] In step S14, the first measuring unit 5a ends charging.

[0042] In step S15, the first measurement unit 5a outputs the charging voltage V1 of the capacitor 52 to the ADC circuit 6a. The ADC circuit 6a converts the charging voltage V1 into digital time data and outputs it to the control unit 7. The time data is, for example, data obtained by converting the time from t1 to t2 shown in FIG. 3C into a digital signal. The control unit 7 acquires the time data. As a result, it is possible to acquire the time (photon arrival time) from time t1 when the synchronization signal s1 is input to time t2 when the detection signal s2 is input.

[0043] In step S16, the first measuring unit 5a discharges the capacitor 52. As a result, the discharge ends at time t3 shown in FIG.

[0044] In step S17, the control unit 7 determines whether the charging voltage V1 of the first measuring unit 5a has reached the threshold voltage Vth. If it has reached the threshold voltage Vth (S17; YES), the process proceeds to step S18; if not, the process returns to step S13.

[0045] In step S18, the second measuring unit 5b starts charging the capacitor 52. That is, since the charging time (delay time T1) of the first measuring unit 5a has elapsed, charging by the second measuring unit 5b starts. At this time, the control unit 7 controls the output of the switch unit 3 to be connected to the second measuring unit 5b.

[0046] 5B, the second measuring unit 5b determines whether or not the detection signal s2 has been input. If the detection signal s2 has been input (S19; YES), the process proceeds to step S20. If not (S19; NO), the process proceeds to step S23.

[0047] In step S20, the second measuring unit 5b ends charging.

[0048] In step S21, the second measurement unit 5b outputs the charging voltage V2 to the ADC circuit 6b. The ADC circuit 6b converts the charging voltage V2 into digital time data and outputs it to the control unit 7. The time data is, for example, data obtained by converting the time from t5 to t6 shown in FIG. 3(d) into a digital signal. The control unit 7 acquires this time data and adds a delay time T1. As a result, it is possible to acquire the time (photon arrival time) from time t4 when the synchronization signal s1 is input to time t6 when the detection signal s2 is input.

[0049] In step S22, the second measuring unit 5b discharges the capacitor 52. As a result, the discharge ends at time t8 shown in FIG.

[0050] In step S23, the control unit 7 determines whether the charging voltage V2 of the second measuring unit 5b has reached the threshold voltage Vth. If it has reached the threshold voltage Vth (S23; YES), the process proceeds to step S24; if not, the process returns to step S19.

[0051] In step S24, the third measurement unit 5c starts charging the capacitor 52. That is, since the charging time (delay time T2) of the first and second measurement units 5a and 5b has elapsed, charging by the third measurement unit 5c starts. At this time, the control unit 7 controls the output of the switch unit 3 to be connected to the third measurement unit 5c.

[0052] In step S25, the third measuring unit 5c determines whether or not the detection signal s2 has been input. If the detection signal s2 has been input (S25; YES), the process proceeds to step S26.

[0053] In step S26, the third measuring unit 5c ends the charging.

[0054] In step S27, the third measurement unit 5c outputs the charging voltage V3 to the ADC circuit 6c. The ADC circuit 6c converts the charging voltage V3 into digital time data and outputs it to the control unit 7. The time data is, for example, data obtained by converting the time from t11 to t12 shown in FIG. 3(e) into a digital signal. The control unit 7 acquires this time data and adds a delay time T2. As a result, it is possible to acquire the time (photon arrival time) from time t9 when the synchronization signal s1 is input to time t12 when the detection signal s2 is input.

[0055] In step S28, the third measuring unit 5c discharges the voltage charged in the capacitor 52. As a result, the capacitor 52 is completely discharged at time t13 shown in FIG.

[0056] As described above, in this embodiment, the photon arrival time from when the synchronization signal s1 is input until when the detection signal s2 is input is measured using the three measurement units 5a to 5c. This allows the capacitance of the capacitor 52 provided in the timing circuit of each of the measurement units 5a to 5c to be reduced, thereby reducing power consumption.

[0057] The following describes how power consumption can be reduced by installing multiple measuring units (three in this embodiment).

[0058] Fig. 6A shows a circuit diagram for one measurement unit equipped with one timing circuit, and Fig. 6B shows a circuit diagram for n measurement units equipped with one timing circuit. In the circuit shown in Fig. 6A, if the current of the current source 51 is I, the voltage applied to the timing circuit is V, and the capacitance of the capacitor 52 is C, then the charge Q stored in the capacitor 52 is "Q = CV", the current I is "I = dQ / dt", the power consumption W is "W = VI", and the electrostatic energy E of the capacitor 52 is "E = (1 / 2) CV ２ It is shown as follows.

[0059] 6B, when n measuring units are used, the capacitance C and voltage V can be reduced by 1 / n. Therefore, the electrostatic energy E is reduced to 1 / n, and the overall power consumption is reduced to 1 / n. ２ It is understood that the amount of heat can be reduced by a factor of 2.

[0060] As described above, the measurement device 100 according to this embodiment is a measurement device that measures the photon arrival time from the input time of the synchronization signal s1 to the input time of the photon detection signal s2, and includes a first input unit 1 that inputs the synchronization signal s1, a second input unit 2 that inputs the photon detection signal s2, and a plurality of measurement units (first to third measurement units 5a to 5c) that measure operating values ​​(charge voltages) according to operating times (charging times), and when the operation (charging) of one measurement unit (first measurement unit 5a) starts at the input time of the synchronization signal s1 and the operating value (charge voltage) of one measurement unit reaches a predetermined threshold voltage Vth, and delay units 4b, 4c that set the operation start time of a measurement unit that will operate (charge) after one measurement unit so that the operation (charging) of the next measurement unit will begin, and each measurement unit starts operation at the operation start time and stops operation (charging) when the operating value (charging voltage) reaches a threshold voltage Vth or when a photon detection signal s2 is input, and further includes a control unit 7 that calculates the photon arrival time when the photon detection signal s2 is input based on the sum of the operating value (charging voltage) of the measurement unit that is operating (charging) and the operating value (charging voltage) of the measurement unit that has finished operating (charging).

[0061] In the measurement device 100 according to this embodiment, the photon arrival time is measured using multiple measurement units (first to third measurement units 5a to 5c), which makes it possible to reduce the power consumption of each measurement unit and to measure the photon arrival time without being affected by the available frequencies.

[0062] In the measuring device 100 according to this embodiment, the capacitance of the capacitor 52 in the timer circuit CK mounted in each measuring unit can be reduced, thereby shortening the time required for discharge and reducing the dead time. Hereinafter, this will be described with reference to FIG.

[0063] 7 is a timing chart showing the change in charging voltage when charging is performed using a single measurement unit. As shown in Figures 7(a) to 7(c), when a voltage corresponding to the photon arrival time is charged using a single measurement unit, if the time from the input of synchronization signal s1 to the input of detection signal s2 is short, as shown from t21 to t22 in Figure 7, the discharge time of the capacitor mounted on the measurement unit is short. Specifically, the discharge of capacitor 52 ends at time t23.

[0064] 7, if the time from the input of the synchronization signal s1 to the input of the detection signal s2 is long, the discharge time of the capacitor mounted on the measurement unit also becomes long, and the discharge ends at t27. For this reason, if the next synchronization signal s1 is input at time t26, for example, charging of the measurement unit cannot start.

[0065] In this embodiment, multiple measurement units (first to third measurement units 5a to 5c) are installed, and when the charging voltage V1 of each measurement unit 5a to 5c reaches the threshold voltage Vth, discharge begins, thereby reducing the dead time due to discharge. Therefore, it is possible to reliably start charging by the measurement units when the synchronization signal s1 is input.

[0066] In this embodiment, each of the measuring units 5a to 5c includes a timing circuit CK in which a current source 51 and a capacitor 52 are connected in series. When charging starts, the current source 51 is activated to pass current through the capacitor 52, and when charging ends, the current source 51 is stopped. The photon arrival time is then calculated based on the charging voltage of the capacitor 52. Therefore, the elapsed time from the input time of the synchronization signal s1 to the input time of the detection signal s2 can be measured using a simple method. Note that, although each of the measuring units 5a to 5c converts the signal into a voltage signal using the capacitor 52 in this embodiment, a counter may also be used to convert the signal into the time domain.

[0067] In this embodiment, the switch unit 3 switches the output destination of the photon detection signal s2 so that it is directed to the measuring unit currently being charged among the measuring units 5a to 5c. Therefore, when the photon detection signal s2 is input, the measuring unit currently being charged can be immediately stopped. This makes it possible to calculate the photon arrival time with higher accuracy.

[0068] [Description of Second Embodiment] Next, a second embodiment will be described. Fig. 8 is a block diagram showing the configuration of a measurement device 101 according to the second embodiment. As shown in Fig. 8, the measurement device 101 differs from the first embodiment in that it includes recording units 8a to 8c.

[0069] Each of the recording units 8a to 8c records charging end data (operation end data) indicating that the charging voltage of the capacitor 52 of the timer circuit CK mounted in each of the measuring units 5a to 5c has reached the threshold voltage Vth. Each of the recording units 8a to 8c outputs a charging end signal (operation end signal) indicating that the charging voltage has reached the threshold voltage Vth to the switch unit 3. Specifically, the recording unit 8a records the end of charging when the charging voltage V1 of the first measuring unit 5a reaches the threshold voltage Vth at time t5 shown in FIG. 3(c), and outputs the charging end signal to the switch unit 3. When the charging end signal from the measuring unit 5a is input, the switch unit 3 switches the output destination of the detection signal s2 to the second measuring unit 5b.

[0070] 3(d), when the charging voltage V2 of the second measuring unit 5b reaches the threshold voltage Vth, the recording unit 8b records the end of charging and outputs a charging end signal to the switch unit 3. When the charging end signal from the measuring unit 5b is input, the switch unit 3 switches the output destination of the detection signal s2 to the third measuring unit 5c.

[0071] That is, each of the recording units 8a to 8c records charging end data indicating that the charging voltage of each of the measuring units 5a to 5c has reached the threshold voltage Vth, and outputs a charging end signal to the switch unit 3. When the charging end signal is received, the switch unit 3 switches the output destination of the photon detection signal s2.

[0072] In this way, in the measuring device 101 according to the second embodiment, when the charging voltage V1 of the first measuring unit 5a reaches the threshold voltage Vth, the output destination of the switch unit 3 is switched from the first measuring unit 5a to the second measuring unit 5b. Furthermore, when the charging voltage V2 of the second measuring unit 5b reaches the threshold voltage Vth, the output destination of the switch unit 3 is switched from the second measuring unit 5b to the third measuring unit 5c. This makes it possible to switch the switch unit 3 more reliably.

[0073] That is, in the first embodiment described above, the time required to charge the capacitor 52 is set in advance, and when the time required for charging has elapsed since the input of the synchronization signal s1, the control unit 7 switches the output destination of the switch unit 3. In contrast, in the second embodiment, the switch unit 3 is switched when the charging voltage of the capacitor 52 reaches the threshold voltage Vth, so that the output destination of the switch unit 3 can be switched more reliably.

[0074] [Description of Third Embodiment] Fig. 9 is a block diagram showing the configuration of a measurement apparatus 102 according to a third embodiment. The measurement apparatus 102 shown in Fig. 9 differs from the first embodiment in that it includes a delay setting unit 9.

[0075] The delay setting unit 9 sets the delay time in the delay units 4 b and 4 c. The delay setting unit 9 acquires the time from when the charging of the capacitor 52 starts until the threshold voltage Vth is reached in the first measurement unit 5 a, for example, and sets this time to be the delay time of the delay unit 4 b.

[0076] Similarly, the delay setting unit 9 obtains the time from when charging of the capacitor 52 starts until the threshold voltage Vth is reached in the second measurement unit 5b, and sets the delay time of the delay unit 4c to be the sum of this time and the delay time of the delay unit 4b. In other words, the delay setting unit 9 sets the delay time of each measurement unit (the delay time of the delay units 4b and 4c) based on the time at which the charging voltage of each measurement unit 5a to 5c reaches the threshold voltage Vth.

[0077] The delay setting unit 9 may also be configured to include a setting input unit (not shown) for a user to set an appropriate delay time through user input.

[0078] In this way, in the measuring device 102 according to the third embodiment, the delay setting unit 9 can set the delay time of each delay unit 4b, 4c to an appropriate value, thereby enabling the switch unit 3 to be switched more reliably.

[0079] [Description of Fourth Embodiment] Next, a fourth embodiment will be described. Fig. 10 is a block diagram showing the configuration of a measuring device 103 according to the fourth embodiment. Fig. 11A is a timing chart showing changes in the synchronization signal, control signal, charging voltage V11 of the first timing circuit 5aA, and charging voltage V21 of the third timing circuit 5bA. Fig. 11B is a timing chart showing changes in the detection signal, control signal, charging voltage V12 of the second timing circuit 5aB, and charging voltage V22 of the fourth timing circuit 5bB.

[0080] As shown in Figure 10, the measuring device 103 according to the fourth embodiment differs from the first embodiment in that the first measuring unit 5a includes two timing circuits and the second measuring unit 5b includes two timing circuits. That is, the first measuring unit 5a includes a first timing circuit 5aA and a second timing circuit 5aB. The second measuring unit 5b includes a third timing circuit 5bA and a fourth timing circuit 5bB. The measuring device 103 according to the fourth embodiment also differs from the first embodiment in that the measuring unit 5a, 5b includes a control signal generating unit 10 that outputs periodically generated control signals. The fourth embodiment is configured to include only two measuring units 5a, 5b.

[0081] In the measuring device 103 according to the fourth embodiment, the control signal generating unit 10 outputs a control signal (see FIGS. 11A(b) and 11B(b)) at a constant cycle, and measures the elapsed time τ1 (see FIG. 11A(c)) from the time the control signal is output to the time the synchronization signal q1 is input. It also measures the elapsed time τ2 (see FIG. 11B(c)) from the time the control signal is output to the time the detection signal p1 is input. The first measuring unit 5a calculates the difference between the elapsed times τ2 and τ1, i.e., "τ2-τ1", as the time (photon arrival time) from the input of the synchronization signal q1 to the input of the detection signal p1.

[0082] That is, the first measuring unit 5a and the second measuring unit 5b each include two timing circuits (first to fourth timing circuits), and the first timing circuit 5aA and the third timing circuit 5bA (one of the timing circuits) measure the elapsed time τ1 (first elapsed time) from the control signal to the synchronization signal. The second timing circuit 5aB and the fourth timing circuit 5bB (the other of the timing circuits) measure the elapsed time τ2 (second elapsed time) from the control signal to the detection signal. The control unit 7 calculates the photon arrival time based on the difference (τ2-τ1) between the second elapsed time τ2 and the first elapsed time τ1.

[0083] 11A and 11B, the operation of the measuring device 103 according to the fourth embodiment will be described below. In Fig. 11A, (a) shows the input time of the synchronization signal, (b) shows the generation time of the control signal, (c) shows the charging voltage V11 of the first timing circuit 5aA, and (d) shows the charging voltage V21 of the third timing circuit 5bA.

[0084] Figure 11B (a) shows the input time of the detection signal, (b) shows the generation time of the control signal, (c) shows the charging voltage V12 of the second timing circuit 5aB, and (d) shows the charging voltage V22 of the third timing circuit 5bA.

[0085] The control signal generating unit 10 shown in Fig. 10 periodically outputs control signals at times t51, t52, ... shown in Fig. 11A(b) and Fig. 11B(b). As shown in Fig. 11A(c), the first timing circuit 5aA of the first measuring unit 5a starts charging at time t51 and stops charging when the synchronization signal q1 is input. Therefore, it is possible to measure the elapsed time τ1 shown in Fig. 11A(c) (the time from time t51 to when the synchronization signal q1 is input).

[0086] 11B(c) and (d), the second timing circuit 5aB of the first measuring unit 5a starts charging at time t51, and the fourth timing circuit 5bB of the second measuring unit 5b starts charging at time t52. Furthermore, as shown in FIG. 11B(c), the second timing circuit 5aB starts charging again at time t53 and stops charging when the detection signal p1 is input. Therefore, the elapsed time τ2 shown in FIG. 11B (the time from time t51 to when the detection signal p1 is input) can be measured.

[0087] Therefore, the control unit 7 shown in FIG. 10 can calculate the time (photon arrival time) from when the synchronization signal q1 shown in FIG. 11A is input until when the detection signal p1 shown in FIG. 11B is input by subtracting the first elapsed time τ1 from the second elapsed time τ2.

[0088] Similarly, based on the difference between the time from the control signal generated at time t52 shown in FIG. 11A to the synchronization signal q2 and the time from time t52 shown in FIG. 11B to the detection signal p2, the time (photon arrival time) from the input of the synchronization signal q2 shown in FIG. 11A to the input of the detection signal p2 shown in FIG. 11B can be calculated.

[0089] In this way, the measuring device 103 according to the fourth embodiment measures the elapsed time τ1 (first elapsed time) until the synchronization signal is input using the periodically generated control signal as a reference, and further measures the elapsed time τ2 (second elapsed time) until the detection signal is input using the control signal as a reference. Then, based on the difference between these two values, "τ2 - τ1," the elapsed time (photon arrival time) from the input of the synchronization signal to the input of the detection signal is calculated.

[0090] Therefore, it is possible to measure the photon arrival time with higher accuracy, even when the time between the input of the synchronization signal and the input of the detection signal is extremely short.

[0091] 10 shows an example in which the measuring device 103 includes two ADC circuits 6a and 6b, but each timing circuit may include its own ADC circuit. That is, the first timing circuit 5aA, the second timing circuit 5aB, the third timing circuit 5bA, and the fourth timing circuit 5bB may each include an ADC circuit.

[0092] The measuring devices 100 to 103 of the present embodiment described above can be implemented as a general-purpose computer system including, for example, a CPU (Central Processing Unit, processor) 901, memory 902, storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), communication device 904, input device 905, and output device 906, as shown in Figure 12. The memory 902 and storage 903 are storage devices. In this computer system, the CPU 901 executes a predetermined program loaded onto the memory 902, thereby realizing the functions of the measuring devices 100 to 103.

[0093] The measurement devices 100 to 103 may be implemented on a single computer or on multiple computers. Also, the measurement devices 100 to 103 may be virtual machines implemented on a computer.

[0094] The programs for the measuring devices 100 to 103 can be stored on a computer-readable recording medium such as a HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), or DVD (Digital Versatile Disc), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0095] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure. The present disclosure may be applied to measurement of photon arrival times in quantum communication, measurement of fluorescence / phosphorescence lifetimes of materials, laser scanning microscopes, etc.

[0096] REFERENCE SIGNS LIST 1 First input section 2 Second input section 3 Switch section 4b, 4c Delay section 5a First measurement section 5b Second measurement section 5c Third measurement section 5aA First timekeeping circuit 5aB Second timekeeping circuit 5bA Third timekeeping circuit 5bB Fourth timekeeping circuit 6a, 6b, 6c ADC circuit 7 Control section 8a, 8b, 8c Recording section 9 Delay setting section 10 Control signal generating section 51 Current source 52 Capacitor 100, 101, 102, 103 Measuring device CK Timekeeping circuit s1 Synchronization signal s2 Detection signal (light detection signal)

Claims

1. A measurement device that measures a photon arrival time from the input time of a synchronization signal to the input time of a photon detection signal, comprising: a first input unit that inputs the synchronization signal; a second input unit that inputs the photon detection signal; a plurality of measurement units that measure operating values ​​according to operating time; and a delay unit that delays the operation start time of a measurement unit that operates after one measurement unit so that operation of one measurement unit starts at the input time of the synchronization signal and operation of the next measurement unit starts when the operating value of the first measurement unit reaches a predetermined threshold, each measurement unit starts operation at the operation start time and stops operation when the operating value reaches the threshold or when the photon detection signal is input; and a control unit that calculates the photon arrival time based on the sum of the operating values ​​of the measurement units in operation and the operating values ​​of the measurement units that have finished operating when the photon detection signal is input.

2. The measuring device according to claim 1, wherein the measuring unit includes a timing circuit having a current source and a capacitor connected in series, the current source is started at the start of operation to pass a current through the capacitor, and the current source is stopped when charging of the capacitor is completed, and the control unit calculates the photon arrival time based on the charging voltage of the capacitor.

3. The measurement device according to claim 1, further comprising a switch section which switches the output destination of the photon detection signal to any one of the plurality of measurement sections.

4. The measurement device of claim 3, further comprising a recording unit which records operation end data indicating that the operation value of the measurement unit has reached the threshold value and outputs an operation end signal to the switch unit, wherein the switch unit switches the output destination of the photon detection signal when the operation end signal is received.

5. The measurement device according to claim 3, further comprising a delay setting unit which sets a delay time for each measurement unit based on the time when the operating value of the measurement unit reaches the threshold value, and the switch unit switches the output destination of the photon detection signal based on the lapse of the delay time set by the delay setting unit.

6. The measurement device according to claim 1, further comprising a control signal generating unit which outputs a control signal which is periodically generated to each measurement unit, each measurement unit comprising two timing circuits, one of the timing circuits measuring a first elapsed time from the control signal to the synchronization signal, and the other of the timing circuits measuring a second elapsed time from the control signal to the photon detection signal, and the control unit calculating the photon arrival time based on the difference between the second elapsed time and the first elapsed time.

7. A measurement method for measuring a photon arrival time from the input time of a synchronization signal to the input time of a photon detection signal, comprising the steps of: starting operation of one of a plurality of measurement units which measure an operating value according to an operating time at the input time of the synchronization signal; executing the operation of each measurement unit so that, when the operating value of the one measurement unit reaches a predetermined threshold, the operation of the measurement unit currently operating is stopped when the photon detection signal is input; and calculating the photon arrival time based on the sum of the operating value of the measurement unit currently operating and the operating value of the measurement unit which has completed operation.

8. A program for causing a computer to function as the measuring device according to any one of claims 1 to 6.

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