Single photon source with photon flux self-calibration function

Abstract

The invention belongs to the technical field of quantum optics, and particularly relates to a single photon source with a photon flux self-calibration function, which comprises a probabilistic single photon source, an attenuator, a coincidence counter and a controller, is internally provided with a quantum benchmark, and accurately calibrates the absolute quantum efficiency of a detector through coincidence measurement by utilizing associated photon pairs generated by spontaneous parametric down-conversion. Therefore, the photon flux is calibrated with high precision, online calibration is supported, and calibration can be completed without shutdown.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of quantum optics, and particularly relates to a single photon source with a photon flux self-calibration function. BACKGROUND

[0002] A probabilistic single photon source is a device that randomly generates single photons through specific quantum optical processes (such as spontaneous parametric down conversion, quantum dot excitation, etc.). The stability and accuracy of the core parameter, photon flux, affect the smooth application of the single photon source. Application scenarios of single photons, such as quantum key distribution (QKD), linear optical quantum computing, quantum-enhanced precision measurement, biological photon microscopy, and deep space optical communication, usually require good short-term stability and small long-term drift error of the photon flux of the single photon source.

[0003] The mainstream technical implementation scheme of the single photon source at present is the spontaneous parametric down conversion (SPDC) scheme. The physical principle is that the pump laser passes through a nonlinear crystal (such as BBO, PPKTP), and generates entangled photon pairs (signal light and idler light) through spontaneous parametric down conversion. The existence of the signal photon is triggered by detecting the idler photon, and a “predictive” single photon source is realized. The probabilistic single photon source may have stability problems due to the following reasons. (1) Crystal temperature sensitivity: temperature fluctuations cause phase matching conditions to deviate, significantly affecting conversion efficiency and photon flux. (2) Pump laser noise transmission: laser intensity fluctuations directly translate into fluctuations in photon pair generation rate. (3) Lack of dynamic compensation: unable to correct flux drift caused by environmental disturbances in real time. SUMMARY

[0004] Based on the above problems, the application integrates an online self-calibration module, which corrects the output photon flux in real time, and feeds back control of the attenuator to compensate for the output flux in real time, thereby reducing the output drift. The technical scheme is as follows:

[0005] A single photon source with a photon flux self-calibration function, comprising a probabilistic single photon source, an attenuator, a coincidence counter, and a controller. The probabilistic single photon source generates two light signals, one of which passes through attenuator one and beam splitter one in sequence into single photon detector one, and the other of which passes through attenuator two and beam splitter two in sequence into single photon detector two. The single photon detector one and the single photon detector two generate electrical pulse signals, and the coincidence counter receives the electrical pulse signals to obtain two single photon rates (photon fluxes) and a double coincidence counting rate (correlated photon pair flux) in combination with the measurement time and the detection efficiency of the detector. The controller receives the photon flux value of the coincidence counter, controls the attenuator one and the attenuator two, and adjusts the attenuation value to reach the set photon flux through a PID algorithm.

[0006] The detection efficiencies of the single-photon detector one and the single-photon detector two are η1 and η2 respectively, and the photon counts are and The generated electric pulse counts are respectively:

[0007] The electric pulse counts generated by the single-photon detector one and the single-photon detector two are respectively.

[0008] Preferably, based on the absolute calibration principle of the detection efficiency of the single-photon detector, the detection efficiency of the single-photon detector is defined as follows:

[0009]

[0010] Wherein, C is the coincidence count value obtained by the coincidence counter for time-intensity correlation analysis of the two electric pulse signals.

[0011] Preferably, for the detector of one of the light paths, even if the quantum efficiency is unknown, the absolute quantum efficiency of the detector of the light path can be obtained through the count and coincidence count of the other light path, without the need for external standard transmission.

[0012] Preferably, the attenuator adopts a MEMS adjustable optical attenuator, and the adjustment frequency is usually above 100 Hz, so as to ensure the output stability.

[0013] Preferably, after the detection efficiency calibration of the two detectors is completed, the photon fluxes of the two light paths can be inversely calculated through the formula N E =N L .

[0014] Preferably, the principle of the probabilistic single-photon source is generally that a pump laser passes through a second-order nonlinear crystal to generate entangled photon pairs through spontaneous parametric down-conversion, and the photon pairs are respectively output from two paths.

[0015] Preferably, two 99:1 beam splitters one and two are respectively arranged on the two light paths; 99% of the photons are transmitted and output, and 1% of the photons are reflected to the single-photon detector one and the single-photon detector two.

[0016] Compared with the prior art, the application has the following beneficial effects:

[0017] (1) The application integrates an online measurement and control module, which can correct the output photon flux in real time in the working mode, so as to reduce the output drift.

[0018] (2) The application supports online calibration, and the calibration can be completed without stopping.

[0019] (3) Using the correlated photon pairs generated by spontaneous parametric down conversion, the absolute quantum efficiency of the detector is accurately calibrated by coincidence measurement, and then the photon flux is calibrated with high precision. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The accompanying drawings illustrate the present application;

[0021] 1-probabilistic single photon source, 201-attenuator one, 202-attenuator two, 301-beam splitter one, 302-beam splitter two, 401-single photon detector one, 402-single photon detector two, 5-coincidence counter, 6-controller. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be described in detail below through specific embodiments and drawings. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations of the technical solutions of the present application, and the specific technical features can be combined with each other.

[0023] A single photon source with a photon flux self-calibration function, comprising a probabilistic single photon source 1, an attenuator one 201, an attenuator two 202, a coincidence counter 5 and a controller 6; the probabilistic single photon source 1 generates two optical signals, one of which passes through the attenuator one 201, the beam splitter one 301 into the single photon detector one 401 in turn; the other optical signal passes through the attenuator two 202, the beam splitter two 302 into the single photon detector two 402 in turn; the single photon detector one 401, the single photon detector two 402 generate electric pulse signals, the coincidence counter 5 receives the electric pulse signals, and the photon rate of the two optical signals, that is, the photon flux, is obtained by combining the measurement time; the controller receives the photon flux value of the coincidence counter 5, controls the attenuator one 201 and the attenuator two 202, and adjusts the attenuation value to reach the set photon flux through the PID algorithm.

[0024] The principle of the probabilistic single photon source 1 is generally that the pump laser passes through a nonlinear crystal (such as BBO, PPKTP), and generates entangled photon pairs (signal light and idle light) through spontaneous parametric down conversion, which are respectively output from the 1 light path and the 2 light path.

[0025] Two beamsplitters, 201 and 202, with a 99:1 beam splitter ratio, are placed on the two optical paths respectively. 99% of the photons are transmitted and output, while 1% are reflected to single-photon detectors 401 and 402. Single-photon detectors 401 and 402 receive photons and generate electrical pulse signals. A coincidence counter 5 receives these electrical pulse signals, and the photon rate (i.e., photon flux) of the two paths is obtained by combining the measured time. Controller 6 receives the photon flux value from the coincidence counter and controls attenuators 201 and 202 (both electronically controlled attenuators). A PID algorithm adjusts the attenuation value to achieve the set photon flux, forming a closed-loop feedback control function to achieve stable photon transmission control in online operating mode.

[0026] Single-photon detectors do not respond to photons with 100% efficiency and possess a certain detection efficiency. Assume the detection efficiencies of single-photon detector 1 (401) and single-photon detector 2 (402) are η1 and η2 respectively, and the photon counts are respectively... and The number of electrical pulses generated is:

[0027]

[0028] Accurately calibrating the detection efficiency of the two detectors is crucial to the accuracy of the output photon flux.

[0029] This invention employs a photon counting detection calibration principle based on parametric down-conversion to complete detector calibration. This principle can be achieved by reusing single-photon detector one, single-photon detector two, and coincidence counter 5 in online operating mode. The detection efficiencies of single-photon detector one and single-photon detector two are:

[0030]

[0031] Where C is the coincidence count value obtained by the coincidence counter from the time correlation characteristic analysis of the two electrical pulse signals.

[0032] As the formula shows, for a single-path detector, even if its quantum efficiency is unknown, the absolute quantum efficiency of a two-path detector can be obtained through counting and coincidence in the single-path detector without the need for external standard quantity transmission. Similarly, if the roles of the single-path and two-path detectors are interchanged, mutual calibration can be achieved, completing single-photon source calibration and providing calibration mode functionality.

[0033] In particular, the attenuator adopts a MEMS tunable attenuator, and the adjustment frequency is usually above 100Hz to ensure output stability;

[0034] Specifically, after completing the detection efficiency calibration of the two detectors, it can be obtained through formula N. E =N L *η calculates the photon flux of the two optical paths.

[0035] In particular, in order to ensure high-precision calibration of the detection efficiency of the single-photon detector, the correlation model of coincidence counting rate and single-photon statistics, dead-time compensation algorithm and optical loss need to be considered.

[0036] In particular, the calibration period is programmable, and the detector efficiency parameter is updated to the controller after calibration.

[0037] The patent proposes a single-photon source with a photon flux self-calibration function, and the purposes of the invention are as follows:

[0038] (1) Integrated online self-calibration module, real-time correction of output photon flux;

[0039] (2) Compensate for the output flux by real-time feedback control attenuator to reduce the output drift;

[0040] (3) Support online calibration, which can be completed without stopping;

[0041] Built-in quantum reference, using the correlated photon pairs generated by spontaneous parametric down-conversion, accurately calibrating the absolute quantum efficiency of the detector through coincidence measurement, and then high-precision calibration of the photon flux.

[0042] The above is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled persons in the technical field, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should be considered as the protection scope of the present application.

Claims

1. A single-photon source with photon flux self-calibration function, characterized in that, The system includes a probabilistic single-photon source, attenuators, a coincidence counter, and a controller. The probabilistic single-photon source generates two optical signals. One optical signal passes through attenuator one and beam splitter one sequentially before entering single-photon detector one. The other optical signal passes through attenuator two and beam splitter two sequentially before entering single-photon detector two. Single-photon detector one and single-photon detector two generate electrical pulse signals. The coincidence counter receives the electrical pulse signals and, by combining the measurement time and the detector's detection efficiency, obtains two single-path photon rates and a dual-path coincidence counting rate. The controller receives the photon flux value from the coincidence counter and controls attenuators one and two, adjusting the attenuation value through a PID algorithm to achieve a set photon flux.

2. The single-photon source with photon flux self-calibration function according to claim 1, characterized in that, Assume the detection efficiencies of single-photon detector 1 and single-photon detector 2 are η1 and η2, respectively, and the photon counts are respectively... and The number of electrical pulses generated are as follows: The counts are the electrical pulses generated by single-photon detector one and single-photon detector two, respectively.

3. The single-photon source with photon flux self-calibration function according to claim 2, characterized in that, The detection efficiency of a single-photon detector is defined as follows: Where C is the coincidence count value obtained by the coincidence counter from the time correlation characteristic analysis of the two electrical pulse signals.

4. The single-photon source with photon flux self-calibration function according to claim 2, characterized in that, Even if the quantum efficiency of a detector in one of the optical paths is unknown, the absolute quantum efficiency of that detector can be obtained by counting and coincidence counting in the other optical path.

5. The single-photon source with photon flux self-calibration function according to claim 1, characterized in that, The attenuator is a MEMS tunable attenuator, with an adjustment frequency typically above 100Hz to ensure output stability.

6. The single-photon source with photon flux self-calibration function according to claim 3, characterized in that, After completing the detection efficiency calibration of the two detectors, it can be obtained by using formula N. E =N L *η calculates the photon flux of the two optical paths.

7. The single-photon source with photon flux self-calibration function according to claim 1, characterized in that, The principle of a probabilistic single-photon source is generally that the pump laser passes through a nonlinear crystal, and entangled photon pairs are generated through spontaneous parametric downconversion, which are then output from two separate paths.

8. The single-photon source with photon flux self-calibration function according to claim 1, characterized in that, Two beam splitters, 99:1, are placed on the two optical paths respectively; 99% of the photons are transmitted and output, and 1% of the photons are reflected to single-photon detectors 1 and 2.

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