KR20160048436A - Apparatus for Detecting Single Photon and Method for the same - Google Patents

Abstract

A single photon detection device can comprise: a first amplifier which amplifies a first gating signal; a first photon detector which detects a single photon according to the amplified first gating signal; a second photon detector which detects a single photon according to a second gating signal; and a mixer which combines an output of the first photon detector with an output of the second photon detector. Also, the single photon detection device can further comprise a second amplifier which amplifies the second gating signal and delivers the amplified second gating signal to the second photon detector. The first amplifier and the second amplifier have variable amplification ratios such that a difference between background signals of the first photon detector and the second photon detector can be adjusted. According to an aspect of the present invention, a single photon detection device and a single photon detection method, which have a low after-pulse noise, high accuracy in detecting a single photon, and the same count rate as a gating frequency, can be provided.

Description

[0001] The present invention relates to a single photon detection apparatus and a single photon detection method,

Embodiments relate to an apparatus and method for detecting a single photon, and more specifically to an apparatus and method for detecting a single photon using a plurality of photon detectors.

A single photon detector capable of detecting a single photon is not only an important component of a quantum cryptography system, but is also very useful in lidar sensors, optical experiments, and the like. In general, an avalanche photodiode (APD) is used as a single photon detector, and the APD operates in a Geiger mode in which the internal gain reaches infinity to detect a single photon.

On the other hand, when the gating signal of the APD has a high frequency of about 1 GHz or more, for example, there is a technical limitation in generating a square wave having a large amplitude as a gating signal. For this reason, in the case of high-speed gating, even when photons are detected, relatively small avalanche occurs. However, since the background signal is generated when the APD operates in the Geiger mode, it is difficult to distinguish the APD from the background signal in the case of a weak avalanche, which reduces the accuracy of the photon detection.

In order to solve this problem, it is possible to increase the accuracy of photon detection by increasing the excess bias voltage. However, in this case, there is also a disadvantage that the after pulse noise of the APD also increases. In particular, the higher the frequency of the gating signal is, the shorter the gating time interval becomes, and the after-pulse noise is not sufficiently eliminated.

To solve this problem, a single photon detection apparatus having the structure shown in Fig. 1 has been proposed as a technique for reducing after-pulse noise. The single photon detector of Figure 1 allows the output signal of APD 11 to be delivered to two ports of power splitter 12 and only the output signal of one of them passes through delay line 13. [ Accordingly, the output signal of the APD 11 and the output signal of the APD 11 delayed by the gating period are input to the combiner 14, and the combiner 14 outputs the comparison result of the two input signals, Can be determined.

The single photon detector of FIG. 1 has the advantage of reducing the after-pulse noise. However, since the output signal of the APD and the delayed output signal of the same APD are compared, the avalanche count rate is reduced to half of the gating frequency .

US 2010/0111305 A1

According to an aspect of the present invention, it is possible to provide a single photon detection apparatus and method that can have a low after-pulse noise, a high accuracy of single photon detection, and a counting rate equal to the gating frequency.

A single photon detection apparatus according to an embodiment includes: a first amplifier that amplifies a first gating signal; A first photon detector for detecting a single photon in accordance with the amplified first gating signal; A second photon detector for detecting a single photon in accordance with a second gating signal; And a coupler coupling the output of the first photon detector and the output of the second photon detector.

A single photon detection method according to an embodiment includes: amplifying a first gating signal; Inputting the amplified first gating signal to a first photon detector; Inputting a second gating signal to a second photon detector; And combining the output signal of the first photon detector with the output signal of the second photon detector.

According to the single photon detection apparatus according to an aspect of the present invention, by detecting the relatively small avalanche with high accuracy, for example, even when the quantum key distribution system is operating at high speed, it can accurately detect a single photon . Also, the quantum bit error rate (QBER) can be reduced by reducing the after-pulse noise. In addition, since the counting rate of the number of single photon detections can be increased, a single photon can be detected more efficiently.

1 is a schematic diagram of a conventional single photon detection device.
2 is a diagram showing a schematic structure of a single photon detection apparatus according to an embodiment of the present invention.
3 is an exemplary graph illustrating the output of a photon detector and combiner of a single photon detection device according to an embodiment of the present invention when a single photon is detected.
4 is an exemplary graph showing the output waveforms of a photon detector and combiner of a single photon detection device according to an embodiment of the present invention when photons are detected and not detected.
5 is a diagram showing a schematic structure of a single photon detection apparatus according to another embodiment of the present invention.
6 is a diagram showing a schematic structure of a single photon detection apparatus according to another embodiment of the present invention.
7 is a flowchart illustrating a procedure of a single photon detection method according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

2 is a diagram showing a schematic structure of a single photon detection apparatus according to an embodiment of the present invention.

Referring to FIG. 2, a single photon detection apparatus 20 according to an embodiment includes a first amplifier 21 for amplifying a first gating signal, a second photon detector 21 for detecting a single photon in accordance with the amplified first gating signal, A second photon detector 23 for detecting a single photon in accordance with the second gating signal and a coupler 24 for combining the output of the first photon detector 22 and the output of the second photon detector 23, . ≪ / RTI >

The first photon detector 22 or the second photon detector 23 may be, for example, an Avalanche Photo Diode (APD). The first photon detector 22 is gated by a first gating signal amplified by the first amplifier 21 and the second gating signal gating the second photon detector 23 is gated by a gate pulse (gate pulse).

The first amplifier 21 amplifies a gating signal or a gating pulse for gating the first photon detector 22. In Figure 2, the first amplifier 21 is illustratively shown coupled to the first photon detector 22, and the first amplifier 21 may be coupled to the second photon detector 23.

The single photon detection apparatus according to the embodiments includes a plurality of photon detectors, each of which has a minute characteristic difference. Because of the difference in characteristics of these devices, each photon detector can have different background signals of different sizes. Therefore, the first amplifier 21 amplifies the gating signal input to the first photon detector 22, thereby adjusting the difference between the background signal of the first photon detector 22 and the background signal of the second photon detector 23 do. For example, the background signal of the first photon detector 22 and the background signal of the second photon detector 23 may be adjusted to be identical. At this time, the first amplifier 21 may have a variable amplification gain by including, for example, a variable resistor.

The coupler 24 receives the output signal of the first photon detector 22 and the output signal of the second photon detector 23 and combines the two signals. For example, the coupler 24 may output a signal indicative of the difference between the two signals by subtracting the signal of the second photon detector 23 from the output signal of the first photon detector 22. In this case, the combiner 24 may be a differential amplifier that outputs the difference between the two signals by differentially amplifying the two signals.

An exemplary output of a photon detector and combiner when a single photon is detected in a single photon detection apparatus according to one embodiment will now be described with reference to Fig.

In a single photon detection apparatus including a plurality of photon detectors, a photon is detected in only one of the plurality of photon detectors by a Mach-Zehnder interferometer phenomenon. That is, the avalanche signal is always generated from only one of the first photon detector and the second photon detector.

For example, when two light pulses divided by a beam splitter of a receiving part Bob of a quantum key distribution system return through a transmitting part (Alice) to a receiving part (Bob) and cause constructive interference, the first photon detector Is clicked to output the avalanche signal 31 from the first photon detector. On the other hand, the second photon detector outputs only the background signal 32 because it is not clicked. Thereafter, the coupler subtracts the output signal 31 of the first photon detector from the output signal 32 of the second photon detector and outputs a signal 33 indicative of the difference between the two signals, so that even when a weak avalanche occurs It is possible to output a peak. Therefore, the coupler outputs, for example, a negative peak as an output signal, so that even a weak avalanche can be detected.

On the other hand, in the case of destructive interference, the first photon detector is not clicked to output only the background signal 34, and the clicked second photon detector outputs the avalanche signal 35. Thus, the combiner outputs a signal 36 having a positive peak by subtracting the output signal 34 of the first photon detector from the output signal 35 of the second photon detector, for example.

Referring again to FIG. 2, the single photon detection apparatus 20 according to an embodiment may further include a comparator 25 connected to the coupler 24, and the specific value may be previously stored in the comparator 25 . The comparator 25 can compare the output signal of the combiner 24 including the avalanche signal with a specific DC value to determine whether a single photon is detected. At this time, the comparator 25 includes a first comparator 26 for comparing the output signal of the combiner 24 with a specific positive value, and a second comparator 27 for comparing the output signal of the combiner 24 with a specific negative value ).

For example, as in the output waveform of Figure 3, when the first photon detector is clicked and the coupler outputs a signal 33 having a negative peak, the second comparator compares the output signal of the coupler with a threshold level ) With a specific sound value. If the output signal of the combiner is equal to or less than the threshold level, the second comparator determines that the photon has been detected, and specifically can determine that the photon has been detected in the first photon detector.

In a similar process, the first comparator compares the output signal of the coupler with a specific amount of the threshold level, and if the output signal is above the threshold level, the photon is detected in the second photon detector.

When the single photon detection apparatus is applied to the quantum cryptography system, the comparator distinguishes between the case where the photon is detected in the first photon detector and the case in which the photon is detected in the second photon detector, and when the photon is detected in the first photon detector, And outputting 1 when a photon is detected in the second photon detector, thereby outputting bits for generating a secure key.

4 is an exemplary graph showing the output waveforms of a photon detector and combiner of a single photon detection device according to an embodiment of the present invention when photons are detected and not detected.

As shown in FIG. 4, the gate pulse 40 for gating the first photon detector and the second photon detector may be a square file of a constant period.

When no photons are detected, the plurality of photon detectors output only background signals, such as signal 41 and signal 42. The background signal appears gated to the gate pulse 40.

On the other hand, when photons are detected, the exemplary outputs of the plurality of photon detectors are as shown in signal 43 and signal 44. The output signal 43 of the first photon detector comprises a weak avalanche signal in the second illustrated period of the gate pulse 40 and a strong avalanche signal in the fourth period. That is, in the second and fourth periods, a single photon is detected in the first photon detector. On the other hand, the output signal 44 of the second photon detector includes a weak avalanche signal in the sixth illustrated period of the gate pulse 40, and a strong avalanche signal in the eighth period. That is, in the sixth and eighth periods, a single photon is detected in the second photon detector.

Looking at the output signal 45 of the combiner, it represents a negative or positive peak in all the intervals in which a single photon is detected, a low peak for a weak avalanche signal, and a high peak for a strong avalanche signal. The output signal 45 of the combiner indicates a negative peak when detected at the first photon detector and a positive peak when detected at the second photon detector so that it is possible to identify at which photon detector the photon was detected.

For example, in one embodiment, the first comparator may compare the signal 45 with a positive DC value to determine whether the signal at or above the positive DC value appears, i.e., at the sixth and eighth periods, It can be seen that a photon has been detected. Likewise, the second comparator compares the negative DC value with the signal 45 to find that photons have been detected in the first photon detector in the second, and fourth, periods when a signal below the negative DC value appears .

5 is a diagram showing a schematic structure of a single photon detection apparatus according to another embodiment of the present invention.

5, a single photon detection apparatus 500 according to another embodiment includes a first amplifier 501, a first photon detector 503, a second photon detector 504, a combiner 507, An amplifier 502 may be included.

The second amplifier 502 amplifies the second gating signal input to the second photon detector 504 so that the background signal of the first photon detector 503 and the second photon detector 503 together with the first amplifier 501 504 in the background signal. At this time, the second amplifier 502 may have a variable amplification ratio by including, for example, a variable resistor, thereby making the background signals of the plurality of photon detectors the same.

In one embodiment, the single photon detection apparatus 500 includes a third amplifier 505 for amplifying the output signal of the first photon detector 503 and a fourth amplifier (not shown) for amplifying the output signal of the second photon detector 504 506). Since the output signals of the first and second photon detectors 503 and 504 also have a small value when the magnitude of the gating signal is small, for example, about 3V, the output signal of the photon detector is amplified . At this time, the third amplifier 505 and the fourth amplifier 506 may have a variable amplification ratio, for example, by including a variable resistor.

FIG. 6 is a schematic structural view of a single photon detection apparatus according to another embodiment of the present invention, and the operation of the single photon detection apparatus will be described with reference to FIG.

A Field Programmable Gate Array (FPGA) 610 included in the single photon detection apparatus includes a pulse generator 611 that generates pulses for gating the photon detectors, and the pulse generator 611 generates different gate pulses And includes a plurality of channels. A first gating signal and a second gating signal, such as the gate pulse 40 shown in FIG. 3, for example, generated in the pulse generator 611 are transmitted to the first amplifier 601 and the second amplifier 602, respectively So that the background signals of the first photon detector 603 and the second photon detector 604 are amplified so as not to make a difference. The amplified gating signal is transmitted to a Bias Tee 614 to which a bias voltage 613 is applied and a bias tee 614 is applied to the first photon detector 603 and the second photon detector 604, .

The output signals of the first photon detector 603 and the second photon detector 604 are amplified by the third amplifier 605 and the fourth amplifier 606 to an amplitude that facilitates analysis and observation of the signal, . The combiner 607 outputs a signal indicative of a peak at a different portion of the two signals, a first comparator 608 for comparing the output signal of the combiner 607 with a positive value, and a second comparator 609). The outputs of the comparators 608 and 609 indicating the occurrence of the avalanche signal are input to the FPGA 610 including the counter 612.

6, the single photon detection apparatus according to an embodiment may further include a counter 612 for counting the number of times of detection of a single photon in accordance with the output signal of the comparators 608 and 609. At this time, the counter 612 includes a first counter 609 and a second comparator 609 for counting the peaks included in the output signal of the first comparator 608 to identify how many photons are detected in any photon detectors. And a second counter for counting the peak included in the output signal of the second comparator.

7 is a flowchart illustrating a procedure of a single photon detection method according to an embodiment of the present invention.

Referring to FIG. 7, the single photon detection method 700 includes amplifying (701) a first gating signal; Inputting (702) the amplified first gating signal to a first photon detector; Inputting a second gating signal to a second photon detector (703); And combining (704) the output signal of the first photon detector and the output signal of the second photon detector.

At this time, the step 701 of amplifying the first gating signal adjusts the difference between the background signal of the first photon detector and the background signal of the second photon detector by amplifying the first gating signal with a variable amplification ratio .

In one embodiment, inputting (703) a second gating signal to a second photon detector comprises: amplifying the second gating signal; And inputting the amplified second gating signal to the second photon detector, wherein inputting the second gating signal to the second photon detector may include inputting the second gating signal included in step (703) The step of amplifying may comprise adjusting the difference between the background signal of the first photon detector and the background signal of the second photon detector by amplifying the second gating signal with a variable amplification ratio.

Further, in one embodiment, combining (704) the output signal of the first photon detector and the output signal of the second photon detector further comprises combining the output signal of the first photon detector and the output signal of the second photon detector And outputting the difference between the first and second signals.

According to another embodiment, a single photon detection method includes: amplifying an output signal of the first photon detector; And amplifying the output signal of the second photon detector.

The method of detecting a single photon according to another embodiment may further include comparing a signal obtained by combining an output signal of the first photon detector and an output signal of the second photon detector with a specific value. Wherein comparing the combined signal of the output signal of the first photon detector and the output signal of the second photon detector to a particular value comprises comparing the combined signal to a specific amount of value, And comparing the signal to a value of a particular tone.

The single photon detection method according to another embodiment may further include a step of counting a single photon detection number according to a result of comparison between the combined signal and a specific value. The step of counting the number of single photon detections may include counting the number of single photon detections according to a result of comparing the combined signal with a specific amount value and comparing the combined signal with a specific sound value And counting the number of single photon detections.

While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. However, it should be understood that such modifications are within the technical scope of the present invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

20: single photon detection device 21: first amplifier
22: First photon detector 23: Second photon detector
24: combiner 25: comparator
26: first comparator 27: second comparator

Claims (20)

A first amplifier for amplifying a first gating signal;
A first photon detector for detecting a single photon in accordance with the amplified first gating signal;
A second photon detector for detecting a single photon in accordance with a second gating signal; And
A combiner coupling an output of the first photon detector and an output of the second photon detector;
And a photodetector coupled to the photodetector. The method according to claim 1,
Wherein the first photon detector or the second photon detector is an avalanche photodiode (APD). The method according to claim 1,
Wherein the first amplifier adjusts a difference between a background signal of the first photon detector and a background signal of the second photon detector. The method according to claim 1,
Wherein the amplification ratio of the first amplifier is variable. The method according to claim 1,
And a second amplifier amplifying the second gating signal and transmitting the amplified second gating signal to the second photon detector. 6. The method of claim 5,
And the amplification ratio of the second amplifier is variable. The method according to claim 1,
A third amplifier for amplifying an output signal of the first photon detector and a fourth amplifier for amplifying an output signal of the second photon detector,
Wherein amplification ratios of the third amplifier and the fourth amplifier are variable. The method according to claim 1,
Wherein the coupler is a differential amplifier that outputs a difference between an output signal of the first photon detector and an output signal of the second photon detector. The method according to claim 1,
A first comparator for comparing an output signal of the combiner with a specific amount of a value, and a second comparator for comparing an output signal of the combiner with a value of a specific tone. 10. The method of claim 9,
And a counter for counting the number of times of detection of a single photon in accordance with an output signal of the first comparator and the second comparator. 11. The method of claim 10,
Wherein the counter comprises a first counter for counting the peak included in the output signal of the first comparator and a second counter for counting the peak included in the output signal of the second comparator. Amplifying a first gating signal;
Inputting the amplified first gating signal to a first photon detector;
Inputting a second gating signal to a second photon detector; And
And combining the output signal of the first photon detector with the output signal of the second photon detector. 13. The method of claim 12,
Wherein the step of amplifying the first gating signal comprises:
And adjusting a difference between a background signal of the first photon detector and a background signal of the second photon detector by amplifying the first gating signal with a variable amplification ratio. 13. The method of claim 12,
Wherein the step of inputting the second gating signal to the second photon detector comprises:
Amplifying the second gating signal; And
And inputting the amplified second gating signal to the second photon detector. 15. The method of claim 14,
Wherein the step of amplifying the second gating signal included in the step of inputting the second gating signal to the second photon detector comprises:
And adjusting the difference between the background signal of the first photon detector and the background signal of the second photon detector by amplifying the second gating signal with a variable amplification ratio. 13. The method of claim 12,
Amplifying an output signal of the first photon detector; And
Further comprising amplifying the output signal of the second photon detector. 13. The method of claim 12,
Wherein combining the output signal of the first photon detector and the output signal of the second photon detector comprises:
And outputting a difference between an output signal of the first photon detector and an output signal of the second photon detector. 13. The method of claim 12,
Comparing the output signal of the first photon detector with the output signal of the second photon detector with a specific amount of the value and comparing the combined signal with a value of a specific tone / RTI > 19. The method of claim 18,
And counting the number of single photon detections according to the comparison result of the combined signal and the specific value. 20. The method of claim 19,
Wherein the step of counting the single photon detection number comprises:
Counting the number of single photon detection times according to a result of comparing the combined signal with a specific amount value and counting a single photon detection number according to a result of comparing the combined signal with a specific sound value / RTI >

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