JP4245956B2 - Single photon detection probability setting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a single photon detection probability setting method for setting a single photon detection probability for a single photon detection device that detects a single photon emitted by a single photon generation source using an avalanche photodiode. Is.
[0002]
[Prior art]
  As a single photon detection device of this type, a single photon detection device 1 shown in FIG. 2 is conventionally known. The single photon detection device 1 includes an avalanche photodiode (hereinafter also referred to as “APD”) 11 for detecting a single photon (hereinafter also referred to as “photon”) Ph emitted from a single photon generation source 2. And a DC (direct current) bias power supply 12 that applies a bias voltage Vb to the APD 11 and a pulse that outputs the pulse voltage Vp to the APD 11 in synchronization with the trigger signal St output together with the emission of the photon Ph by the single photon generation source 2. A generator 13 and a counter 14 that detects the presence or absence of incidence of a photon Ph based on a pulse signal (output signal) Sp output from the APD 11 and counts the number of incidence of the photon Ph are provided. In this case, the APD 11 is connected to the single photon generation source 2 via the optical cable OC. As an example, the APD 11 has an anode terminal grounded via a resistor and a cathode terminal connected to the DC bias power source 12 and the pulse generator 13. The counter 14 has a comparator function, inputs the trigger signal St output by the single photon generation source 2, and within a predetermined period thereafter, the pulse signal Sp having an output level exceeding a set threshold value Is detected by the APD 11 or not.
[0003]
  When counting (detecting) photons Ph using this single photon detection device 1, first, a positive polarity lower than the breakdown voltage (voltage V1 shown in FIG. 3) is applied to the cathode terminal of the APD 11 by the DC bias power source 12. A bias voltage Vb is applied. Next, the photon Ph is emitted to the single photon generation source 2. At this time, the single photon generation source 2 outputs a trigger signal St and emits a photon Ph in synchronization with the output of the trigger signal St. In response to this, the pulse generator 13 generates a pulse voltage Vp having a pulse width of 1 ns to 2 ns as an example in synchronization with the trigger signal St, and applies the generated pulse voltage Vp to the cathode terminal of the APD 11. Specifically, the pulse generator 13 inputs a trigger signal St so that a pulse voltage Vp can be applied to the APD 11 in accordance with the incidence timing of the photon Ph to the APD 11, and then a preset delay time Td has elapsed. At this time, a pulse voltage Vp is generated and applied to the APD 11. As a result, as shown in FIG. 3, the pulse voltage Vp output from the pulse generator 13 is combined with the bias voltage Vb applied by the DC bias power supply 12, so that a voltage exceeding the breakdown voltage V1 is applied to the APD 11. Applied to the cathode terminal. In this state, the photons Ph emitted from the single photon generation source 2 are incident on the APD 11, whereby the carriers generated in the APD 11 are amplified and output as a pulse signal Sp as shown in FIG.
[0004]
  On the other hand, the counter 14 receives the trigger signal St output from the single photon generation source 2, and detects whether or not the pulse signal Sp having an output level exceeding a predetermined threshold is output by the APD 11. Start processing. In this process, when the pulse signal Sp exceeding the threshold value is output, one count is made assuming that the photon Ph is incident. Next, when the output of the pulse voltage Vp by the pulse generator 13 is stopped, the voltage applied to the cathode terminal falls below the breakdown voltage V1. As described above, in the single photon detection device 1, the APD 11 is avalanche breakdown only when the trigger signal St is output (a short period in which the incidence of the photon Ph is expected). The output of the dark pulse (pulse signal Sp output exceeding the threshold due to a cause other than the incidence of the photon Ph) due to the APD 11 due to noise or the like is reduced. In addition, by applying a pulse voltage Vp having a narrow pulse width to the APD 11 in synchronization with the trigger signal St output from the single photon generation source 2, the avalanche breakdown time of the APD 11 is shortened, so that a dark pulse is generated. It is further reduced. Therefore, according to the single photon detection apparatus 1, the number of incident photons Ph can be accurately measured to some extent by counting the number of pulse signals Sp by reducing the generation of dark pulses. It has become.
[0005]
  Such a single photon detection device 1 is applied to a receiver for quantum cryptography communication in an information security communication device as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-234265.
[0006]
  In this type of information security communication apparatus, data communication is performed by expressing information (“0” or “1”) using the polarization state of a single photon. Specifically, on the transmission side, the single photon generator (1) generates a single photon in synchronization with the input trigger signal. The polarization modulation element (2) controls and encodes the polarization state of the input single photon based on the setting content by the encoding device (3). The polarization modulation element (2) outputs the polarized single photon to the optical cable as the transfer means (6). In this case, on the transmission side, a trigger signal is also output in synchronization with a single photon. On the other hand, on the receiving side, the polarization separation element (9, 10) selects the optical path according to the polarization state of the single photon, so that the single photon detection devices (11, 12, 13,. A single photon is incident on 14). Each single photon detection apparatus (11-14) detects the single photon output from the transmission side using a photon detection element. Furthermore, on the receiving side, the ellipsometer (15), the time slot identification means (16), and the decoding device (17) are connected to each single photon detector (11-14) based on the detection results of the single photon detectors (11-14). Decode information encoded in photons. At this time, like the single photon detection device 1, a single photon detection device using an APD as a light detection element is used as each single photon detection device (11-14).
[0007]
  By the way, in the single photon detection apparatus 1 using the APD, the pulse voltage Vp is generated based on the input timing of the trigger signal St and the APD 11 is shifted to the avalanche breakdown state. The detection probability of the photon Ph (probability of generation of the pulse signal Sp) depends on at which timing within the applied period the photon Ph is incident and what value the threshold value set in the counter 14 is set to. Changes significantly. For example, when the single photon detection device 1 using the APD 11 is applied to the information security communication device described above, the distance between the reception side and the transmission side changes for each installation location of the information security communication device. As a result, the length of the optical cable OC through which the photon Ph passes changes, and as a result, the input timing of the trigger signal St and the photon Ph to the single photon detection device 1 changes. For this reason, in the single photon detection device 1, first, the setting of the incident timing of the photon Ph to the APD 11 during the period in which the pulse voltage Vp is applied, that is, from the input of the trigger signal St to the pulse generator 13 to the application of the pulse voltage Vp. The delay probability Td is set first, and then the threshold value is set for the counter 14, thereby setting the detection probability of the photon Ph.
[0008]
  Conventionally, when setting the detection probability for the photon Ph for the single photon detection device 1, the photon Ph and the trigger signal St are output to the single photon detection device 1 using a tester including the single photon generation source 2. However, by sequentially changing the delay time Td and the threshold value and measuring the pulse height distribution indicating the threshold value dependency on the detection probability of the photon Ph for each changed delay time Td, FIG. The delay time dependency data for the wave height distribution as shown in FIG. On the other hand, when the information security communication apparatus is installed, a desired wave height distribution is determined with reference to the delay time dependency data regarding the wave height distribution, and the delay time Td in the pulse generator 13 is adjusted so as to be the wave height distribution. By doing this, the incident timing of the photon Ph to the APD 11 during the period in which the pulse voltage Vp is applied is set. Specifically, an example of setting the wave height distribution (hereinafter also referred to as “wave height distribution A”) indicated by reference numeral A in FIG. 4 will be described. First, the threshold value of the counter 14 is fixed to a constant value (for example, 20 mV), and in this state, processing for measuring the detection probability of the photon Ph in the APD 11 is performed. Next, it is determined whether or not the measured detection probability is an occurrence probability on the wave height distribution A (in this case, 4%). If not, the detection probability is measured (measured). The delay time is changed until the detected probability coincides with the occurrence probability corresponding to the threshold value in the wave height distribution A (in this example, 4%). When the measured detection probability coincides with the occurrence probability corresponding to the threshold value in the wave height distribution A, the adjustment of the delay time Td for the pulse generator 13 is finished. Thereafter, referring to the set wave height distribution (wave height distribution A), a threshold value at which the detection probability of the photon Ph with respect to the single photon detection device 1 becomes a desired value is obtained, and the obtained threshold value is set in the counter 14. To do. Thereby, the setting of the detection probability of the photon Ph for the single photon detection apparatus 1 is completed.
[0009]
[Patent Document 1]
  Japanese Patent Laid-Open No. 11-234265 (page 8, FIG. 1)
[0010]
[Problems to be solved by the invention]
  However, the conventional single photon detection probability setting method for the single photon detector 1 has the following problems to be solved. That is, in the conventional single photon detection probability setting method, when the delay time Td in the pulse generator 13 is set, the delay time Td in the pulse generator 13 is set in a state where the threshold value for the counter 14 is fixed to a constant value. The detection probability of the photon Ph at this fixed threshold (the generation probability of the pulse signal Sp) is set so as to be positioned on the desired wave height distribution determined with reference to the delay time dependency data. Yes. However, as shown in FIG. 4, each of the wave height distributions for each delay time Td is in the range above the threshold value (about 6 mV) where the occurrence rate of dark pulses is at a low level that does not cause a practical problem. Since the waveform intersects with the wave height distribution at one point, the delay time Td setting method based on one threshold value has a problem that it may be erroneously set to another wave height distribution. For example, even when the delay time Td is adjusted by fixing the threshold value to 20 mV so as to be the wave height distribution A, the wave height distribution of the code B (hereinafter referred to as “wave height distribution”) at the point where the threshold value is 20 mV. May also be set to the wave height distribution B by mistake.
[0011]
  The present invention has been made in view of such problems, and a main object of the present invention is to provide a single photon detection probability setting method capable of accurately setting the detection probability of a single photon.
[0012]
[Means for Solving the Problems]
  In order to achieve the above object, a single photon detection probability setting method according to the present invention includes an avalanche photodiode to which a single photon emitted from a single photon generation source is incident, and a breakdown voltage applied to the avalanche photodiode. A combined voltage of the DC bias power source for applying a predetermined voltage and the predetermined voltage when a preset delay time has elapsed from the input of the trigger signal output together with the emission of the single photon by the single photon generation source Generates a pulse voltage exceeding the breakdown voltage and applies the pulse voltage to the avalanche photodiode, and an output level of an output signal output by the avalanche photodiode in a state where the pulse voltage is applied is a predetermined threshold. A sensor that detects the incidence of the single photon when the value is exceeded. A single-photon detection probability setting method for setting a single-photon detection probability for a single-photon detection device comprising a counter, the delay time for the pulse generator and the threshold value for the counter Delay time dependence of the pulse height distribution created by measuring the pulse height distribution indicating the threshold dependence on the detection probability of the incidence of the single photon by the counter in turn for each of the changed delay times. A first detection probability corresponding to a threshold of an arbitrary value in the predetermined wave height distribution in the sex data, andA detection probability measured when a threshold value of an arbitrary value is set for the counter matches a second threshold value corresponding to a threshold value of another arbitrary value in the predetermined wave height distribution. Finding the delay time at which the detection probability matches the detection probability measured when the threshold value of the other arbitrary value is set for the counter while changing the delay time for the pulse generator, Set the delay time when the coincidence for the pulse generator,Thereafter, the single photon detection probability is set by setting the threshold for the counter to an arbitrary value.
[0013]
  Also, the single photon detection probability setting method according to claim 2 is the single photon detection probability setting method according to claim 1, wherein the threshold value for the counter is set to the threshold value of the arbitrary value. In the state where the detection probability by the counter is measured and the measured detection probability and the first detection probability are compared with each other, and the threshold value for the counter is set to the other arbitrary value The process of measuring the detection probability by the counter and comparing the measured detection probability and the second detection probability with each other, the measured detection probability corresponding to the threshold of the arbitrary value is the first The pulse generator until the measured detection probability corresponding to the detection probability of 1 and corresponding to the threshold value of the other arbitrary value matches the second detection probability. Run while changing the delay time for data.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
  DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a single photon detection probability setting method according to the present invention will be described with reference to FIGS. It is assumed that the delay time dependency data on the wave height distribution in the single photon detection device 1 shown in FIG. 4 is measured in advance. Hereinafter, the same components as those of the single photon detection device 1 described above are denoted by the same reference numerals, and redundant description is omitted.
[0015]
  When setting the single photon detection probability, first, in the single photon detection apparatus 1 shown in FIG. 2, the relative incident timing of the photon Ph with respect to the APD 11 during the period in which the pulse voltage Vp is applied is set. Specifically, as shown in FIG. 1, first, with reference to the delay time dependency data for the wave height distribution shown in FIG. 4, a desired (predetermined) delay time Td in the delay time dependency data is set. The corresponding wave height distribution is determined (step 20). For example, it is assumed that the wave height distribution A in FIG. 4 is determined.
[0016]
  Next, the threshold value for the counter 14 is set to an arbitrary value Vth1 (step 21). Subsequently, the detection probability Pd of the photon Ph in the counter 14 is measured (step 22). The measured detection probability Pd and the first detection probability Pa1 corresponding to the threshold value (value Vth1) in the determined wave height distribution A Are compared (step 23). At this time, when the detection probabilities Pd and Pa1 do not match, the delay time Td for the pulse generator 13 is changed (step 24), and the steps 22 and 23 are repeatedly executed to detect the detection probability Pd as the first detection. It is made to coincide with the probability Pa1. For example, as shown in FIG. 4, when the threshold value is set to the value Vth1 (20 mV), the detection probability Pd of the counter 14 is 4% because the first detection probability Pa1 in the wave height distribution A is 4%. The delay time Td is changed as follows.
[0017]
  After completing the above processing, the threshold value for the counter 14 is set to another arbitrary value Vth2 (step 25). Next, the detection probability Pd of the photon Ph in the counter 14 is measured (step 26), and the measured detection probability Pd and the second detection probability Pa2 corresponding to the threshold value (value Vth2) in the determined wave height distribution A are obtained. Compare (step 27). At this time, when the detection probabilities Pd and Pa2 do not match, the delay time Td for the pulse generator 13 is changed (step 28), and the steps 26 and 27 are repeatedly executed to obtain the detection probability Pd as the second detection probability. It is made to coincide with the probability Pa2. When the delay time Td is changed in step 27 when the detection probabilities Pd and Pa2 do not match, the threshold value Vth2 is set to a voltage lower than the value Vth1 (for example, 8 mV) as shown in FIG. When the measured detection probability Pd is larger than the second detection probability Pa2 (6%) in the wave height distribution A, the detection probability Pd approaches the second detection probability Pa2 by increasing the delay time Td. When the detection probability Pd is smaller than the second detection probability Pa2, the detection probability Pd tends to approach the second detection probability Pa2 by decreasing the delay time Td. Conversely, when the threshold value Vth2 is set to a voltage higher than the value Vth1, the tendency is opposite to the above tendency. Therefore, when changing the delay time Td, the detection probability Pd can be easily matched with the second detection probability Pa2 by changing based on this tendency.
[0018]
  Next, the detection probabilities Pd when the threshold values are set to the values Vth1 and Vth2 are measured again (step 29), and the measured detection probabilities Pd are compared with the corresponding detection probabilities Pa1 and Pa2 (step 29). 30). When at least one of the detection probabilities Pd does not match the corresponding detection probability (Pa1 or Pa2), the above steps 21 to 30 are repeatedly executed until the detection probabilities Pd and the corresponding detection probabilities Pa1 and Pa2 match. . On the other hand, in step 30, when the detected detection probabilities Pd and the corresponding detection probabilities Pa1 and Pa2 coincide with each other, the detection probabilities for the photons Ph with respect to the threshold value have the characteristics shown in the wave height distribution A. Then, it is determined that the delay time Td (that is, the incidence timing of the photon Ph with respect to the APD 11 during the period in which the pulse voltage Vp is applied) is set for the pulse generator 13, and the process proceeds to the next process.
[0019]
  Subsequently, with reference to the wave height distribution A shown in FIG. 4, a threshold value at which the detection probability for the photon Ph by the single photon detection device 1 becomes a desired value is obtained, and the obtained threshold value is given to the pulse generator 13. Set (step 31). Thereby, the setting of the detection probability Pd for the photon Ph for the single photon detection device 1 is completed.
[0020]
  Thus, according to this single photon detection probability setting method, the delay time Td is set when the incident timing of the photon Ph to the APD 11 of the single photon detection device 1 is set during the period in which the pulse voltage Vp is applied. The detection probabilities Pa1 and Pa2 for the thresholds of two different values Vth1 and Vth2 in the wave height distribution determined by referring to the delay time dependency data for the wave height distribution shown in FIG. 4 and two different values A delay time Td that matches each detection probability Pd measured when Vth1 and Vth2 are set as threshold values in the counter 14 is obtained, and the obtained delay time Td is set in the pulse generator 13 as the delay time Td. Thus, the detection probability of the photon Ph with respect to the threshold value is set (adjusted) reliably and accurately so as to be the characteristic of the determined wave height distribution It can be. Therefore, by subsequently setting the threshold value based on the determined wave height distribution, the detection probability of the photon Ph in the single photon detection device 1 can be reliably set to a desired value.
[0021]
  The present invention is not limited to the configuration shown in the above-described embodiment of the present invention. For example, the delay time Td (that is, the pulse voltage Vp) is applied to the pulse generator 13 so that the detection probability for the photon Ph with respect to the threshold value has the characteristics indicated by the wave height distribution A (desired wave height distribution). It is also possible to configure the single photon detection device to automatically perform the operation of setting the photon Ph incidence timing on the APD 11 in the period. As shown in FIG. 5, the single photon detection device 1 </ b> A includes a memory 41, an input unit 42, and a control unit 43 in addition to the configuration of the single photon detection device 1. In this case, the memory 41 prestores delay time dependency data on the wave height distribution for each delay time Td shown in FIG. The input unit 42 includes, for example, an operation panel and a keyboard, and is configured to be able to input specific data Ds indicating a desired wave height distribution and threshold values Vth (Vth1, Vth2) for the counter 14 to the control unit 43. Yes. The control unit 43 is configured by a CPU or the like, and has a function of setting the threshold value Vth input from the input unit 42 in the counter 14 and measuring the detection probability Pd of the photon Ph in the counter 14. Further, the control unit 43 has a function of adjusting the delay time Td of the pulse generator 13. Further, when the specific data Ds is input from the input unit 42, the control unit 43 determines the wave height distribution specified by the input specific data Ds among the plurality of wave height distributions stored in the memory 41 as a desired wave height. A function of calculating the detection probabilities Pa1 and Pa2 of the photons Ph corresponding to the input threshold value Vth in the determined wave height distribution by determining the distribution and referring to the delay time dependency data on the determined wave height distribution I have.
[0022]
  In the single photon detection apparatus 1A configured as described above, the control unit 43 that receives the specific data Ds and the threshold values Vth1 and Vth2 from the input unit 42 executes Steps 20 to 30 shown in FIG. As a result, the delay time Td is automatically set for the pulse generator 13 so that the detection probability for the photons Ph with respect to the threshold values Vth1 and Vth2 has the characteristic indicated by the desired wave height distribution. As an example, when the specific data Ds indicating the wave height distribution A is input from the input unit 42, the control unit 43 refers to the memory 41 to change the wave height distribution specified by the specific data Ds to a desired wave height distribution (an example) As a wave height distribution A) (step 20). Next, the control unit 43 sets the threshold value Vth1 input from the input unit 42 in the counter 14, thereby setting the threshold value of the counter 14.Setting(Fixed)(Step 21). Next, in this state, the control unit 43 measures the detection probability Pd of the photon Ph in the counter 14 (step 22), and corresponds to the measured detection probability Pd and the threshold value Vth1 calculated with reference to the memory 41. In comparison with the first detection probability Pa1 to be performed (step 23), the delay time Td of the pulse generator 13 is changed (step 24), thereby matching the detection probability Pd by the counter 14 with the first detection probability Pa1. Execute the process.
[0023]
  Next, the control unit 43 sets the threshold value of the counter 14 by setting the threshold value Vth2 input from the input unit 42 in the counter 14.Setting(Fixed)(Step 25). Next, in this state, the control unit 43 measures the detection probability Pd of the photon Ph in the counter 14 (step 26), and corresponds to the measured detection probability Pd and the threshold value Vth2 calculated with reference to the memory 41. By comparing the second detection probability Pa2 (step 27) and changing the delay time Td of the pulse generator 13 (step 28), the detection probability Pd by the counter 14 is made to coincide with the second detection probability Pa2. Execute the process. Next, the control unit 43 sequentially sets the threshold values Vth1 and Vth2 for the counter 14 and measures the detection probabilities Pd at the threshold values Vth1 and Vth2 (step 29). It is determined whether or not the detection probabilities Pd at the values Vth1 and Vth2 coincide with the detection probabilities Pa1 and Pa2 (step 30). In step 30, the control unit 43 repeatedly executes steps 21 to 30 until the detection probabilities Pd at the measured threshold values Vth1 and Vth2 coincide with the first detection probabilities Pa1 and Pa2. Thus, the control unit 43 automatically sets the delay time Td for the pulse generator 13 so that the detection probability Pd for the photon Ph for each threshold value has the characteristics shown in the wave height distribution A. Thereafter, the control unit 43 sets the threshold value Vth input from the input unit 42 in the counter 14. Thereby, the setting of the detection probability of the photon Ph for the single photon detection device 1A is completed.
[0024]
  Thus, according to this single photon detection apparatus 1A, the control unit 43 detects the photon Ph with respect to the threshold value Vth based on the specific data Ds input from the input unit 42 and the threshold values Vth1 and Vth2. By automatically setting the delay time Td for the pulse generator 13 so that the probability Pd has a characteristic indicated by a desired wave height distribution specified by the specific data Ds, the detection probability of the photon Ph with respect to the threshold is determined. It can be set (adjusted) quickly, easily, reliably and accurately so as to match the characteristics of the wave height distribution. Therefore, by subsequently setting a threshold value based on the determined wave height distribution, the detection probability of the photon Ph in the single photon detection apparatus 1A can be quickly and easily set to a desired value. it can.
[0025]
  The present invention is not limited to the configuration shown in the above-described embodiment of the present invention. For example, the single photon detection devices 1 and 1A can be applied not only to the reception device of quantum cryptography communication in the information security communication device but also to any other device. Furthermore, in the embodiment of the present invention, the configuration in which the counter 14 is provided with a comparator function and the threshold value is set has been described as an example. However, instead of this configuration, a comparator is provided between the APD 11 and the counter 14. It is also possible to employ a configuration in which a threshold value is set for this comparator.
[0026]
【The invention's effect】
  As described above, according to the single photon detection probability setting method according to the present invention, the first detection corresponding to the threshold value of an arbitrary value in the predetermined wave height distribution in the delay time dependency data regarding the wave height distribution. probabilityAnd thisValue thresholdSet for the counter (Fixed)didThe second detection probability corresponding to the threshold value of any other value in the predetermined wave height distribution and the threshold value of this other arbitrary value are matched with the counter. The delay time that matches the detection probability measured when setting is set while changing the delay time for the pulse generator. MeThus, the delay time for the pulse generator can be set reliably and accurately so that the characteristic of the detection probability of a single photon with respect to the threshold value matches the characteristic indicated by the determined pulse height distribution. Therefore, by setting the threshold value based on the determined wave height distribution, the single photon detection probability in the single photon detection device can be reliably set to a desired value.
[Brief description of the drawings]
FIG. 1 is a flowchart for explaining a single photon detection probability setting method according to an embodiment of the present invention;
FIG. 2 is a configuration diagram of a single photon detection apparatus 1;
3 shows the timing of input of a trigger signal St to the pulse generator 13, the timing of incidence of the photon Ph to the APD 11, and the timing of applying the pulse voltage Vp to the APD 11 when detecting the single photon by the single photon detection device 1. FIG. It is a timing chart which shows a relationship.
FIG. 4 is a characteristic diagram showing delay time dependency data for a pulse height distribution of the single photon detection apparatus 1;
FIG. 5 is a configuration diagram of a single photon detection apparatus 1A.
[Explanation of symbols]
      1,1A single photon detector
      2 Single photon source
    11 Avalanche photodiode
    12 DC bias power supply
    13 Pulse generator
    14 counter
    41 memory
    42 Input section
    43 Control unit
    Ds specific data
    OC optical cable
    Pd detection probability
    Ph photon
    Sp pulse signal
    St trigger signal
    Vb bias voltage
    Vp pulse voltage
  Vth threshold
    Td delay time

Claims (2)

An avalanche photodiode to which a single photon emitted by a single photon generation source is incident, a DC bias power source that applies a predetermined voltage lower than a breakdown voltage to the avalanche photodiode, and the single photon generation source When a preset delay time elapses from the input of a trigger signal output together with the emission of one photon, a pulse voltage whose combined voltage with the predetermined voltage exceeds the breakdown voltage is generated and applied to the avalanche photodiode And a counter that detects the incidence of the single photon when the output level of the output signal output by the avalanche photodiode exceeds a predetermined threshold value when the pulse voltage is applied. The single photon detection accuracy of the single photon detector A single photon detection probability setting method for setting a
The delay time for the pulse generator and the threshold value for the counter are sequentially changed to change the pulse height distribution indicating the threshold dependence of the detection probability of the incidence of the single photon by the counter. A first detection probability corresponding to a threshold value of an arbitrary value in the predetermined wave height distribution in the delay time-dependent data for the wave height distribution created by measuring each and a threshold value of the arbitrary value The second detection probability corresponding to the threshold value of any other value in the predetermined wave height distribution and the other arbitrary The delay time corresponding to the detection probability measured when setting a threshold value of the value for the counter is the delay time for the pulse generator Asked while changing between,
Set the delay time when the coincidence for the pulse generator,
Thereafter, the single photon detection probability setting method of setting the detection probability of the single photon by setting the threshold value for the counter to an arbitrary value. A process of measuring the detection probability by the counter in a state in which the threshold value for the counter is set to the threshold value of the arbitrary value, and comparing the measured detection probability and the first detection probability with each other; ,
A process of measuring the detection probability by the counter in a state where the threshold value for the counter is set to the other arbitrary value and comparing the measured detection probability and the second detection probability with each other;
The measured detection probability corresponding to the threshold of the arbitrary value matches the first detection probability, and the measured detection probability corresponding to the threshold of the other arbitrary value is the second The single-photon detection probability setting method according to claim 1, wherein the method is executed while changing the delay time for the pulse generator until the detection probability coincides with the detection probability.

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