Calibration method based on few-photon calibration system

Abstract

The invention belongs to the technical field of few-photon calibration, and relates to a calibration method based on a few-photon calibration system. The calibration system comprises a light source and a detection system. The light source comprises a laser, an attenuator, a collimator and a control circuit, the laser is used for emitting the light source, and the attenuator and the collimator are combined to adjust the intensity of the output light source; the detection system comprises a receiving system and a detector, and the receiving system is used for receiving the output light source and detecting and measuring an optical signal through the detector; the light source is connected with the detection system, and the calibration method comprises the following steps: S1, preparing a single photon source by using an attenuation pulse method; s2, setting light source emission energy; s3, evaluating the performance of the single-photon source according to the single-photon property index; and S4, evaluating the performance of the single photon source according to the isotropy of the photons. The optical system is calibrated by designing the few-photon light source and the emission system, so that the minimum energy of the few-photon light source is in a single-photon magnitude, and technical support and reference are provided for sensitive detection of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of few-photon calibration, and in particular relates to a calibration method based on a few-photon calibration system. Background Art

[0002] In the large-scale construction of high-voltage power grids, gas-insulated switchgear has been widely used in power systems due to its compact structure, flexible configuration, easy installation, long maintenance cycle and many other advantages. In recent years, with the rapid development of urbanization and the large-scale construction of high-voltage power grids, power accidents caused by gas-insulated switchgear failures have also increased, directly affecting the safety of energy transmission channels and the stability of the entire power grid system. Therefore, the calibration of the power system discharge signal of gas-insulated switchgear is of great significance.

[0003] Optical detection of discharge signals in power systems requires extremely high sensitivity, and has high requirements for the intensity range and divergence angle of the light source of the calibration system. Currently, there is a lack of calibration systems based on few photons. High-intensity light sources and large-angle divergence angles can cause specular reflections of the surrounding environment of the detection system, resulting in the detection system being unable to reflect the true status of the detection.

[0004] Therefore, a calibration system based on few-photons is urgently needed to achieve the purpose of conducting research on few-photon calibration technology for detection optical systems; by designing a few-photon light source and an emission system to calibrate the optical system, the lowest energy of the few-photon light source can be achieved at the single-photon level, providing technical support and benchmark for sensitive detection of the system. Summary of the invention

[0005] In view of this, the present invention discloses a calibration method based on a few-photon calibration system.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A calibration method based on a few-photon calibration system, the calibration system comprising a light source and a detection system; the light source comprises a laser, an attenuator and a collimator connected in sequence through a control circuit, the laser is used to emit the light source, and the attenuator and the collimator are combined to adjust the intensity of the output light source; the detection system comprises a receiving system and a detector, the receiving system is used to receive the output light source, and detect and measure the optical signal through the detector; the light source is connected to the detection system, and the calibration method comprises the following steps:

[0008] S1. Set the light source emission energy;

[0009] S1. Preparation of single photon source using attenuated pulse method;

[0010] S3. Evaluate the performance of the single photon source based on the single photon index;

[0011] S4. Evaluate the performance of the single-photon source based on the photon homogeneity.

[0012] Furthermore, in step S1, the light source emission energy is set at 10 photons / mm 2 -1000 photons / mm 2 .

[0013] Further, in step S2, the single photon source preparation method includes:

[0014] S21. The pulse laser outputs a beam of coherent light. The quantum state of the coherent light output by the pulse laser is determined by the wave function of the coherent light. The wave function of the coherent light is defined as

[0015]

[0016] Where α is the eigenvalue of the coherent state annihilation operator, |n> represents the Fock state with n photons;

[0017] S22, calculating the probability of the coherent light containing more than one photon, clarifying the distribution of the number of photons output by the pulsed laser, and then determining whether further attenuation is required, wherein the probability of the coherent light containing more than one photon is calculated by:

[0018]

[0019] Where n represents the average number of photons per unit time. The smaller the average number of photons n of coherent light is, the higher the probability of generating multiple photons P is. n＞1 The lower;

[0020] S23. Using an attenuator, the average number of photons output by the pulse laser is regulated to be close to a single photon level.

[0021] Further, in step S3, the photon number fluctuation of the output single photon source satisfies The sub-Poisson distribution of .

[0022] Further, in step S3, the single-photon property of the single-photon source is given by the second-order correlation function g (2) (τ) is determined by using the HBT experiment. The measurement process includes:

[0023] S31. Use a beam splitter to split the single photon source into two paths, place photon detectors on each path, record the time when the photons arrive, and make statistics on the time difference between the two detectors to obtain the second-order correlation function g of the photons. (2) (τ), where τ is the time difference between the two detectors;

[0024] S32, a single-photon source that satisfies the single-photon property, its second-order correlation function g (2)(τ) is 0 at τ = 0; when g (2) The value of (0) is close to 0, and the single-photon source has good single-photon properties.

[0025] Further, in step S4, the photon homogeneity of the single photon source is measured using the HOM interference experiment:

[0026] S41. A beam of single photon source is used to generate entangled photon pairs through the spontaneous parametric down-conversion process, and a beam splitter is used to separate the photon pairs into two paths; an adjustable delay line is placed on one of the paths to accurately control the time difference between the two photons arriving at the single photon detector; two single photon detectors are placed at the ends of the two paths to record the arrival of the photons;

[0027] S42, input a pair of single photons into two input ports of a beam splitter respectively; the beam splitter guides the two photons to two different paths respectively; by adjusting the delay line, the two photons are gradually approached in time until they arrive at the single photon detector almost at the same time; the single photon detector is used to record the arrival of the photons and count the coincidence count, that is, the number of events in which two photons are detected at the same time;

[0028] S43, by measuring the coincidence count, determine the similarity of the two photons in each degree of freedom. If the coincidence count is high, the two photons have a high degree of identity. Observe the change of the coincidence count with the delay time to present an interference pattern. By analyzing the interference pattern, further quantify the identity of the photons.

[0029] S44. When two photons are indistinguishable, they will show a bunching effect at the detector, that is, the two photons will tend to be output from the same output port, and the coincidence count reaches the maximum value at this time; by comparing the actually measured coincidence count with the theoretical expected value, the similarity of the two photons in each degree of freedom is evaluated, thereby judging their identicalness.

[0030] The beneficial effects of the present invention are:

[0031] To achieve low-energy calibration, by designing a few-photon light source and detection system, the lowest energy calibration at the single-photon level can be achieved, that is, the energy of a single photon can be accurately controlled and measured, thereby achieving high-sensitivity calibration. Provide technical support and benchmarks, through the design and implementation of the calibration system, it can provide technical support and benchmarks for system sensitive detection, and realize the application of weak light detection technology in the power field.

[0032] Providing a high-precision single-photon source. By using the attenuated pulse method to prepare the single-photon source, it can be ensured that the photon emission characteristics of the single-photon source are stable and meet expectations. This method can effectively control the photon emission process and avoid the situation of multiple photon emission, thereby providing a high-precision single-photon source.

[0033] To ensure the sensitive detection of the system, by setting the emission energy of the light source, it can be ensured that the system can receive sufficient photon signals during the detection process, thereby improving the sensitivity of the system. This is very important for achieving high-precision calibration and detection, because it can ensure that the system can work stably under different conditions.

[0034] Evaluate the performance of the single photon source. By judging the performance of the single photon source according to the single photon index, the performance of the calibration system can be optimized. For example, if it is found that the photon number fluctuation does not satisfy the sub-Poisson distribution, then corresponding measures can be taken to improve the photon emission characteristics of the single photon source, thereby improving the overall performance of the calibration system.

[0035] Providing technical support and benchmarks, by judging the performance of single-photon sources based on the photon homogeneity, the lowest energy of few-photon light sources can be achieved at the single-photon level, providing technical support and benchmarks for sensitive detection of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the calibration system based on few photons in the present invention. DETAILED DESCRIPTION

[0037] In order to better understand the present invention, the content of the present invention is further clearly described below in conjunction with the embodiments and the accompanying drawings, but the protection content of the present invention is not limited to the following embodiments. In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details.

[0038] Example

[0039] like Figure 1 As shown, the purpose of this embodiment is to design a calibration method based on a few-photon calibration system.

[0040] The few-photon calibration system includes a light source 1 and a detection system 2. The light source 1 includes a laser, an attenuator and a collimator connected in sequence through a control circuit, the laser is used to emit a light source, and the attenuator and the collimator are combined to adjust the intensity of the output light source. The detection system 2 includes a receiving system and a detector, the receiving system is used to receive the output light source, and the received light source is detected and measured by the detector. The light source is connected to the detection system through a cable or an optical fiber.

[0041] The calibration method comprises the following steps.

[0042] S1. Set the emission energy of the light source. By precisely controlling the emission energy of the light source, it is possible to further ensure that the number of photons emitted each time is kept at the single-photon level, thus avoiding multi-photon events and improving the purity of the single-photon source. In step S1, the emission energy of the light source is set at 10 photons / mm 2 -1000 photons / mm 2 .

[0043] S2. Prepare a single photon source using the attenuated pulse method. This step ensures that the number of photons emitted by the light source is as small as possible, reaching the single photon level. This method can control the generation of photons so that only one photon is generated each time, thereby realizing a low-photon light source.

[0044] The light source 1 involved in this application is the key and core of the implementation scheme. From a quantum point of view, a single photon is a Fock state with a photon number n=1. An ideal single photon source can generate only one single photon in any time interval, that is, on demand. Each emitted single photon is completely indistinguishable; the emission probability of a single photon is 100% and the photon number fluctuation is 0. Since there are still many difficulties and challenges in realizing an ideal single-photon source in reality, the common methods for preparing single-photon sources in experiments currently include single-atom method, quantum dot method, crystal color center method, spontaneous parametric down-conversion method, and attenuated pulse light method. Among them, the single-atom method, quantum dot method, and crystal color center method have similar principles and can all be regarded as a two-level system, using electrons to stimulate radiation to emit a photon; the spontaneous parametric down-conversion method uses ultrashort pulses to pump nonlinear crystals to produce time-domain correlated entangled photon pairs; and the attenuated pulse light method uses strong attenuation based on the statistical probability distribution of photons to achieve single-photon output, which is also the most practical single-photon source preparation method currently.

[0045] S21. The present application uses the attenuated pulse method to prepare a single photon source. The quantum state of the coherent light output by the pulse laser is determined by the wave function of the coherent light, and the wave function of the coherent light is defined as

[0046]

[0047] In the formula, α is the eigenvalue of the coherent state annihilation operator, and |n> represents the Fock state with n photons. From the above formula, we can see that the coherent state is a quantum state with an uncertain number of photons, and its photon number obeys the Poisson distribution,

[0048]

[0049] Among them, P n represents the probability of emitting n photons per unit time, Represents the average number of photons per unit time.

[0050] S22, calculating the probability of the coherent light containing more than one photon, clarifying the distribution of the number of photons output by the pulsed laser, and then determining whether further attenuation is required, wherein the probability of the coherent light containing more than one photon is calculated by:

[0051]

[0052] It can be seen from this that the smaller the average number of photons in coherent light, the lower the probability of generating multiple photons.

[0053] S23. Using an attenuator, the average number of photons output by the pulse laser is regulated to be close to a single photon level.

[0054] The present application utilizes an attenuator in step S23 to adjust the average number of photons output by the laser pulse.

[0055] However, due to the quantum nature of photons, even when the average number of photons is very low, there is no guarantee that each pulse will contain only one photon. In fact, most pulses may contain no photons, and only a few pulses may contain one or more photons. For example, there is more than 95% confidence that multi-photons are not generated, but 90% of the time no photons pass through at all. This means that when the pulse light decays to a very weak level, most pulses do not contain photons, so this results in a very low rate of single photon generation. The purpose of doing this in step S23 is to reduce the number of photons output by the laser, so that the number of photons contained in each pulse is smaller, close to the level of single photons, so as to obtain more accurate results in the experiment.

[0056] S3. Evaluate the performance of the single-photon source based on single-photon indicators. Evaluate the performance of the single-photon source based on single-photon indicators to ensure the quality of the single-photon source. These indicators include the coherence of photons, single-photon probability, etc., which can help understand whether the performance of the single-photon source meets expectations.

[0057] The most important indicator for judging the performance of a single-photon source is the single-photon property, which is determined by the second-order correlation function g (2) (τ) can be determined by HBT experiment. In the experiment, the light path is divided into two by a beam splitter, the arrival time of the photons is detected in both paths, and the time difference between the two paths is statistically calculated, and the HBT effect will occur. Since a single photon cannot be split, it is impossible to detect the photon in both paths at the same time. The statistical data will be concave at the time τ = 0, that is, g (2) (0) = 0. For coherent light and thermal light field, we have g (2) (0) = 1 and g (2) (0)=2.

[0058] In step S3, the single-photon property of the single-photon source is determined by the second-order correlation function g(2) (τ) is determined by using the HBT experiment. The measurement process includes:

[0059] S31. Use a beam splitter to split the single photon source into two paths, place photon detectors on each path, record the time when the photons arrive, and make statistics on the time difference between the two detectors to obtain the second-order correlation function g of the photons. (2) (τ), where τ is the time difference between the two detectors;

[0060] S32, a single-photon source that satisfies the single-photon property, its second-order correlation function g (2) (τ) is 0 at τ = 0; when g (2) The value of (0) is close to 0, indicating that the single-photon source has good single-photon property.

[0061] S4. Evaluate the performance of the single photon source based on photon homogeneity. Evaluate the homogeneity of photons to further confirm the performance of the single photon source. The homogeneity of photons refers to the degree of similarity of photons in all degrees of freedom, which is very important for applications such as quantum information processing and quantum computing.

[0062] Another indicator for judging the performance of a single-photon source is the photon homogeneity, which is measured using the HOM interference experiment. Two photons can interfere because the photons are indistinguishable from each other. From the output quantum state of the HOM interference experiment, it can be seen that the input two photons have a bunching effect after passing through the interferometer, that is, the situation where two photons are output from one output port respectively does not exist. The photon bunching phenomenon occurs because the two terms describing the output of two photons from one output port respectively interfere with each other. It is worth noting that the photon bunching effect can only occur when the two input photons are perfectly indistinguishable (degrees of freedom such as frequency, input time and polarization). Therefore, the coincidence count measured by the single-photon detector can determine the homogeneity of the two incident photons.

[0063] In step S4, the specific measurement process of the photon homogeneity of the single photon source using the HOM interference experiment is:

[0064] S41. A beam of single photon source is used to generate entangled photon pairs through the spontaneous parametric down-conversion process, and a beam splitter is used to separate the photon pairs into two paths; an adjustable delay line is placed on one of the paths to accurately control the time difference between the two photons arriving at the detector; two single photon detectors are placed at the ends of the two paths to record the arrival of the photons;

[0065] S42, input a pair of single photons into two input ports of a beam splitter respectively; the beam splitter guides the two photons to two different paths respectively; by adjusting the delay line, the two photons are gradually brought close in time until they arrive at the detector almost at the same time; a single photon detector is used to record the arrival of the photons and count the coincidence count, that is, the number of events in which two photons are detected at the same time;

[0066] S43. Determine the similarity of the two photons in each degree of freedom by measuring the coincidence count. If the coincidence count is high, it indicates that the two photons have a high degree of identity. Observe the change of the coincidence count with the delay time to present an interference pattern. By analyzing the interference pattern, further quantify the identity of the photons.

[0067] S44. If two photons are perfectly indistinguishable, they will show an obvious bunching effect at the detector, that is, the two photons will tend to be output from the same output port, and the coincidence count reaches a maximum value at this time; by comparing the actually measured coincidence count with the theoretical expected value, the similarity of the two photons in each degree of freedom is evaluated, thereby judging their exact identity.

[0068] For coherent light, such as laser, the number of photons per unit time satisfies the Poisson distribution, and the photon number fluctuations Light sources such as incandescent lamps, sunlight, and LEDs have photon number distributions that conform to the thermal light field distribution form, and photon number fluctuations Photons tend to gather together, and this distribution is called super-Poisson distribution, and the corresponding photons show a bunching effect; while for quantum light fields such as single-photon sources, the photon number fluctuations satisfy In such a sub-Poisson distribution, photons exhibit an anti-bunching effect, and photons tend to move away from each other.

[0069] Therefore, for the prepared single-photon source, the photon number fluctuation of the single-photon source needs to satisfy Sub-Poisson distribution, photons show anti-bunching effect, and photons tend to move away from each other. Because if the photon number fluctuation of the single photon source does not satisfy the sub-Poisson distribution, then the calibration system may have errors, because the calibration system is calibrated based on the photon emission characteristics of the single photon source. If the photon emission process is unstable or there is multiple photon emission, the result of the calibration system will be affected, thereby reducing the accuracy of the calibration system. By judging whether the photon number fluctuation of the single photon source satisfies the sub-Poisson distribution, it can be ensured that the calibration system can work stably under different conditions. This is very important for the long-term operation and maintenance of the calibration system, because it can prevent system failures caused by unstable photon emission characteristics. Moreover, by judging the photon number fluctuation of the single photon source, the performance of the calibration system can be optimized. For example, if it is found that the photon number fluctuation does not satisfy the sub-Poisson distribution, then corresponding measures can be taken to improve the photon emission characteristics of the single photon source, thereby improving the overall performance of the calibration system.

[0070] Through the above four steps, we can ensure that the minimum energy of the few-photon light source is at the single-photon level, thus providing technical support and benchmark for the sensitive detection of the system. This calibration method helps to improve the sensitivity and accuracy of quantum detection systems and promote the development of quantum information science.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A calibration method based on a few-photon calibration system, characterized in that: The calibration system includes a light source and a detection system; the light source includes a laser, an attenuator and a collimator connected in sequence through a control circuit, the laser is used to emit light, and the attenuator and collimator are combined to adjust the intensity of the output light source; the detection system includes a receiving system and a detector, the receiving system is used to receive the output light source, and detect and measure the light signal through the detector; the light source is connected to the detection system, and the calibration method includes the following steps: S1. Set the light source emission energy; S1. Preparation of single photon source using attenuated pulse method; S3. Evaluate the performance of the single photon source based on the single photon index; S4. Evaluate the performance of the single-photon source based on the photon homogeneity.

2. A calibration method based on a few-photon calibration system according to claim 1, characterized in that: In step S1, the light source emission energy is set at 10 photons / mm 2 -1000 photons / mm 2 .

3. A calibration method based on a few-photon calibration system according to claim 2, characterized in that: In step S2, the single photon source preparation method includes: S21. The pulse laser outputs a beam of coherent light. The quantum state of the coherent light output by the pulse laser is determined by the wave function of the coherent light. The wave function of the coherent light is defined as Where α is the eigenvalue of the coherent state annihilation operator, |n> represents the Fock state with n photons; S22, calculating the probability of the coherent light containing more than one photon, clarifying the distribution of the number of photons output by the pulsed laser, and then determining whether further attenuation is required, wherein the probability of the coherent light containing more than one photon is calculated by: In the formula Represents the average number of photons per unit time, the average number of photons of coherent light The smaller the probability of producing multiple photons, P n＞1 The lower; S23. Using an attenuator, the average number of photons output by the pulse laser is regulated to be close to a single photon level.

4. A calibration method based on a few-photon calibration system according to claim 3, characterized in that: In step S3, the photon number fluctuation of the output single photon source satisfies The sub-Poisson distribution of .

5. A calibration method based on a few-photon calibration system according to claim 4, characterized in that: In step S3, the single-photon property of the single-photon source is determined by the second-order correlation function g (2) (τ) is determined by using the HBT experiment. The measurement process includes: S31. Use a beam splitter to split the single photon source into two paths, place photon detectors on each path, record the time when the photons arrive, and make statistics on the time difference between the two detectors to obtain the second-order correlation function g of the photons. (2) (τ), where τ is the time difference between the two detectors; S32, a single-photon source that satisfies the single-photon property, its second-order correlation function g (2) (τ) is 0 at τ = 0; when g (2) The value of (0) is close to 0, and the single-photon source has good single-photon properties.

6. A calibration method based on a few-photon calibration system according to claim 5, characterized in that: In step S4, the photon homogeneity of the single photon source is measured using the HOM interferometer experiment: S41. A beam of single photon source is used to generate entangled photon pairs through the spontaneous parametric down-conversion process, and a beam splitter is used to separate the photon pairs into two paths; an adjustable delay line is placed on one of the paths to accurately control the time difference between the two photons arriving at the single photon detector; two single photon detectors are placed at the ends of the two paths to record the arrival of the photons; S42, input a pair of single photons into two input ports of a beam splitter respectively; the beam splitter guides the two photons to two different paths respectively; by adjusting the delay line, the two photons are gradually approached in time until they arrive at the single photon detector almost at the same time; the single photon detector is used to record the arrival of the photons and count the coincidence count, that is, the number of events in which two photons are detected at the same time; S43, by measuring the coincidence count, determine the similarity of the two photons in each degree of freedom. If the coincidence count is high, the two photons have a high degree of identity. Observe the change of the coincidence count with the delay time to present an interference pattern. By analyzing the interference pattern, further quantify the identity of the photons. S44. When two photons are indistinguishable, they will show a bunching effect at the detector, that is, the two photons will tend to be output from the same output port, and the coincidence count reaches the maximum value at this time; by comparing the actually measured coincidence count with the theoretical expected value, the similarity of the two photons in each degree of freedom is evaluated, thereby judging their identicalness.

Images