CN111307282B - Single photon source preparation system and method - Google Patents
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Abstract
The invention relates to a single photon source preparation system and a method, wherein the system comprises an optical pulse signal generator, an attenuation module, a first beam splitting module and a monitoring module, wherein the first beam splitting module is used for receiving an optical pulse signal output by the attenuation module, dividing the optical pulse signal into two paths, outputting one path of optical pulse signal to the monitoring module, and directly outputting the other path of optical pulse signal as a single photon pulse signal of the system; the monitoring module is used for receiving one path of optical pulse signals output by the first beam splitting module, performing coincidence counting on the optical pulse signals to obtain a coincidence counting result, and mapping the coincidence counting result and the average photon number of the single optical pulse signals by utilizing a mapping relation between a pre-calibrated coincidence counting result and the average photon number of the single optical pulse signals to obtain and output average photon number information of the single optical pulse signals; the invention realizes the real-time monitoring of the output single photon pulse signal through the monitoring module, and solves the problem that the prior art can not carry out accurate real-time monitoring on the output state of a single photon source.
Description
Technical Field
The invention relates to the technical field of optics, in particular to a single photon source preparation system and a single photon source preparation method.
Background
With the continuous breakthrough of quantum technology in theory and experiment, leading-edge technologies such as quantum communication and quantum detection are receiving more and more attention, and the preparation of a single photon signal source only containing a single photon is an indispensable important link. In order to realize the controllable output of single photon pulse signals, the conventional methods comprise a quantum dot single photon source and an attenuation single photon source, the quantum dot single photon source technology has a good technical prospect, but the technology is not mature, the large-scale application cannot be realized, and the attenuation single photon source still is a more reliable single photon source preparation scheme at present. However, due to the limitation of the precision of the laser and the attenuation device, the preparation of the attenuation single photon source still has many defects, such as low single photon output efficiency, limited precision of the attenuation device and the light energy measuring equipment, incapability of directly measuring and monitoring the output state of the single photon source after attenuation in real time, incapability of obtaining stable single photon source output, and the like, and cannot meet strict scientific research and application requirements.
Disclosure of Invention
The invention provides a single photon source preparation system, which solves the problem that the state of a single photon pulse signal output by a single photon source cannot be monitored in real time.
The invention is realized by the following technical scheme:
the invention provides a single photon source preparation system, which comprises an optical pulse signal generator and an attenuation module, wherein the optical pulse signal generator outputs an optical pulse signal, and the optical pulse signal is attenuated and then output by the attenuation module;
the first beam splitting module is used for receiving the optical pulse signals output by the attenuation module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the monitoring module, and directly outputting the other path of optical pulse signals as single photon pulse signals of the system;
the monitoring module is used for receiving one path of optical pulse signals output by the first beam splitting module, performing coincidence counting on the optical pulse signals to obtain a coincidence counting result, and mapping the coincidence counting result and the average photon number of the single optical pulse signals by utilizing a mapping relation between a pre-calibrated coincidence counting result and the average photon number of the single optical pulse signals to obtain and output average photon number information of the single optical pulse signals;
in the technical scheme, an optical pulse signal generator outputs an initial optical pulse signal by adopting a pulse laser, the initial optical pulse signal is attenuated by an attenuation module, the energy of the optical pulse signal is attenuated to a single photon magnitude order to meet the requirement of single photon preparation, then the optical pulse signal subjected to attenuation processing is output to a first beam splitting module, the first beam splitting module is a first beam splitter and is used for splitting the input optical pulse signal into two paths according to equal proportion, one path of optical pulse signal is output to a monitoring module, and the monitoring module is an HBT experimental system; taking the other path of optical pulse signal as the output end of the single photon source to output a single photon pulse signal; after receiving the optical pulse signals output by the first beam splitting module, the monitoring module performs coincidence counting operation on the optical pulse signals, and mapping the coincidence counting result and the average photon number of the optical pulse signals by using a mapping relation of a pre-calibrated coincidence counting result and the average photon number of the optical pulse signals to obtain the average photon number information of the single photon pulse signals; because the first beam splitter divides the optical pulse signals into two paths according to an equal proportion, and the two paths of optical pulse signals are equivalent to each other, according to the result output by the monitoring module, the state of the single photon pulse signal output by the other path can be represented, and the real-time monitoring of the output state of the single photon source preparation system is completed.
As a further improvement of the present invention, the monitoring module includes a fourth beam splitting module, a first single-photon detector, a second single-photon detector and a data processing unit;
the fourth beam splitting module is used for receiving the optical pulse signals output by the first beam splitting module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the first single-photon detector, and outputting the other path of optical pulse signals to the second single-photon detector;
the first single-photon detector and the second single-photon detector are used for receiving the optical pulse signals output by the fourth beam splitting module, carrying out photon counting detection on the photon number in each received optical pulse signal and outputting the counting result to the data processing unit;
the data processing unit is used for receiving a first photon counting result output by the first single-photon detector and a second photon counting result output by the second single-photon detector, performing coincidence counting on the first photon counting result and the second photon counting result to obtain a coincidence counting result, and mapping to obtain and output average photon number information of the single-photon pulse signal by using a mapping relation between the coincidence counting result and the average photon number of the single-photon pulse signal, which is calibrated in advance;
in the technical scheme, the fourth beam splitting module is a fourth beam splitter; after receiving the optical pulse signal output by the first beam splitter, the fourth beam splitter further divides the optical pulse signal into two paths according to the equal proportion, outputs one path of optical pulse signal to the first single-photon detector, outputs the other path of optical pulse signal to the second single-photon detector, counts and detects the photon number in the optical pulse signal through the first single-photon detector and the second single-photon detector, outputs a photon counting result to the data processing unit, performs coincidence counting operation on the counting results of the two single-photon detectors through the data processing unit, and maps and obtains and outputs the average photon number information of the single-photon pulse signal by using the mapping relation between the pre-calibrated coincidence counting result and the average photon number of the single-photon signal through the nondetachability of photons; by adopting the structure of the monitoring module in the technical scheme, the average photon number in the output single photon pulse signal can be accurately monitored on the photon magnitude, so that the real-time monitoring of the state of the single photon source output single photon pulse signal is completed.
Further, the single photon source preparation system also comprises a polarization module; the polarization module comprises a light path selection module, a second beam splitting module, a polarization control module and a polarization measurement module;
the optical path selection module is used for receiving the optical pulse signal output by the optical pulse signal generator and selectively outputting the optical pulse signal to the polarization control module or selectively outputting the optical pulse signal to the attenuation module;
the polarization control module is used for receiving the optical pulse signal output by the optical path selection module, controlling the optical pulse signal to reach a specific polarization state, and outputting the optical pulse signal with the specific polarization state to the second beam splitting module;
the second beam splitting module is used for receiving the optical pulse signal output by the polarization control module, dividing the optical pulse signal into two paths, outputting one path of optical pulse signal to the polarization measurement module, and outputting the other path of optical pulse signal to the attenuation module;
the polarization measurement module receives the optical pulse signal output by the second beam splitting module, measures the optical pulse signal to obtain polarization state information of the optical pulse signal, and outputs the polarization state measurement information to the monitoring module;
in the technical scheme, the optical path selection module is an optical switch, the optical switch receives an initial optical pulse signal output by a pulse laser, and the optical pulse signal is selectively output to the polarization control module or directly output to the attenuation module, so that the whole system can selectively generate a single-photon pulse signal in a polarization state or generate a single-photon pulse signal in a non-polarization state to meet the actual diversified output requirements; when the polarization control module receives the optical pulse signal output by the optical switch and controls the optical pulse signal to reach any required polarization state, the optical pulse signal with the polarization state is output to a second beam splitting module, the second beam splitting module is a second beam splitter, the second beam splitter divides the optical pulse signal into two paths according to the proportion of 10:90, 10% of the optical pulse signal is output to the polarization measurement module, and 90% of the optical pulse signal is output to the attenuation module; the polarization measurement module receives the optical pulse signal output by the second beam splitter, measures the polarization state of the optical pulse signal, and outputs the polarization state measurement information to the data processing unit in the monitoring module, the data processing unit judges whether the angle of the polarization state in the optical pulse signal is too large or too small according to the polarization state measurement information, if the angle of the polarization state in the optical pulse signal is too large, the polarization control module is subjected to polarization feedback control to reduce the angle of the polarization state, if the angle of the polarization state is too small, the polarization control module is subjected to polarization feedback control to increase the angle of the polarization state, and therefore the polarization state in the optical pulse signal is adjusted, and the control of the polarization state is more accurate and stable.
Further, the attenuation module comprises a variable attenuation module, a third beam splitting module, an optical energy measuring module and a fixed attenuation module;
the variable attenuation module is used for receiving the optical pulse signal output by the optical path selection module and receiving the other optical pulse signal output by the second beam splitting module, performing variable attenuation processing on the optical pulse signal, and outputting the processed optical pulse signal to the third beam splitting module;
the third beam splitting module is used for receiving the optical pulse signals processed by the variable attenuation module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the optical energy measuring module, and outputting the other path of optical pulse signals to the fixed attenuation module;
the optical energy measuring module is used for receiving one path of optical pulse signals output by the third beam splitting module, measuring the optical energy value of the optical pulse signals and outputting the optical energy value measuring result to the monitoring module;
the fixed attenuation module is used for receiving the other path of optical pulse signal output by the third beam splitting module, performing fixed attenuation processing on the optical pulse signal and outputting the processed optical pulse signal to the first beam splitting module;
in the technical scheme, after the optical pulse signal enters the variable attenuation module through the second beam splitter or enters the variable attenuation module through the optical switch, the variable attenuation module performs variable attenuation on the energy of the optical pulse signal, so that the flexible control on the energy of the output optical pulse signal is realized; after the optical pulse signal enters a third beam splitting module through the variable attenuation module, the third beam splitting module is a third beam splitter, the third beam splitter divides the optical pulse signal into two paths according to the proportion of 99:1, 99% of the optical pulse signal is output to the optical energy measuring module, and 1% of the optical pulse signal is output to the fixed attenuation module; after the optical energy measuring module receives the optical pulse signal output by the third beam splitter, measuring the energy in the optical pulse signal, and outputting the optical energy value measuring result in the optical pulse signal to a data processing unit in the monitoring module; when the fixed attenuation module receives the optical pulse signal output by the third beam splitter, the fixed attenuation module accurately attenuates the optical pulse signal, so that the energy of the attenuated optical pulse signal reaches the single photon magnitude and is output to the first beam splitter; according to the technical scheme, after attenuation processing of the optical pulse signal is completed, the single photon magnitude optical pulse signal is obtained, photon energy is measured in proportion through the optical energy measuring module, the optical energy value measuring result is input into the data processing unit of the monitoring module, and the data processing unit performs feedback control on the variable attenuation module.
The monitoring module is further used for receiving polarization state measurement information output by the polarization measurement module and an optical energy value measurement result output by the optical energy measurement module, performing feedback control on the polarization control module according to the polarization state measurement information, and performing feedback control on the variable attenuation module according to the coincidence counting result and the optical energy value measurement result;
in the technical scheme, a data processing unit in a monitoring module judges whether the angle of the polarization state in the optical pulse signal is too large or too small according to the measurement information of the polarization state, if so, the polarization control module is subjected to polarization feedback control to adjust the polarization state angle to be small, if the polarization state angle is too small, the polarization control module is subjected to polarization feedback control to adjust the polarization state angle to be large, thereby adjusting the angle of the polarization state in the optical pulse signal, ensuring the control of the polarization state to be more accurate and stable, and the data processing unit in the monitoring module calculates the output energy of the optical pulse signal according to a certain proportion according to the measurement result of the optical energy value, and simultaneously combines the coincidence counting result of the optical pulse signal input into the monitoring module, and performing energy feedback control on the variable attenuation module, adjusting the multiple of energy attenuation of the optical pulse signal, and ensuring the stability of single photon pulse signal output.
Further, a single photon source preparation method is provided, the single photon source preparation system is adopted for preparation, the method comprises the steps of optical pulse signal monitoring and output, and the steps are as follows:
and according to the coincidence counting result, mapping relation between the preset calibrated coincidence counting result and the average photon number of the single-photon optical pulse signal is utilized to map and obtain the average photon number information of the single-photon optical pulse signal and output.
Further, before the step of monitoring and outputting the optical pulse signal, the method also comprises an optical pulse signal attenuation step, wherein the step specifically comprises the step of performing variable attenuation processing on the received optical pulse signal by adopting a variable attenuation module; a third beam splitting module is adopted to divide the optical pulse signals after variable attenuation processing into two paths for output; the optical energy measuring module is used for measuring the optical energy value of one path of optical pulse signals output by the third beam splitting module, and the optical energy value measuring result is output to the monitoring module; and the fixed attenuation module is adopted to perform fixed multiple attenuation processing on the other path of optical pulse signal output by the third beam splitting module and then output the optical pulse signal to the first beam splitting module.
Further, before the optical pulse signal attenuation step, the method further comprises the following steps:
s101: the optical pulse signal output by the optical pulse signal generator is output to the optical path selection module, and the optical pulse signal is selectively output to the polarization control module or the attenuation module;
s102: when the optical pulse signal is selected to be output to the polarization control module, the polarization control module controls the optical pulse signal to reach a specific polarization state; and the second beam splitting module is also adopted to divide the optical pulse signal with the polarization state output by the polarization control module into two paths, the polarization measurement module is adopted to measure the polarization information of one path of optical pulse signal, the polarization measurement information is output to the monitoring module, and the other path of optical pulse signal is directly transmitted to the variable attenuation module.
Further, after the polarization measurement information is output to the monitoring module, the monitoring module performs feedback control on the polarization control module according to the polarization measurement information;
and after the optical energy value measurement result is output to the monitoring module, the monitoring module performs feedback control on the variable attenuation module according to the optical energy value measurement result and the coincidence counting result.
Further, the calibration method according with the mapping relationship between the counting result and the average photon number of the single-light pulse signal, which is calibrated in advance, comprises the following steps:
s201: the number of photons contained in each single photon pulse signal approximately follows a Poisson random process, that is, when the average number of photons contained in the output single photon pulse signal is mu, the probability of outputting the single photon pulse signal containing n photons is shown as formula (1):
wherein N is 1,2,3, …, N; n is the maximum value of the number of photons contained in the photon pulse;
s202: supposing that the single-photon pulse signal is divided into two paths after passing through a beam splitter with the beam splitting ratio of S1: S2, the two paths of single-photon pulse signal light respectively enter a first single-photon detector and a second single-photon detector, and meanwhile, the response efficiency of the first single-photon detector and the response efficiency of the second single-photon detector to the single-photon pulse signal containing n photons are eta respectively1nAnd η2nThe dark counting rates of the two single photon detectors are respectively R1darkAnd R2darkIn the case where the gating frequency is R, the probability of occurrence of dark count noise every time the door is opened is as shown in equation (2):
s203: suppose the probability of the back pulse of the first single-photon detector and the probability of the back pulse of the second single-photon detector are respectively P1spAnd P2spThe noise probability of the first single-photon detector and the noise probability of the second single-photon detector are respectively P1noiseAnd P2noiseAccording to the counting working characteristics of the single-photon detector, the following can be obtained:
wherein, mu 'and mu' are the average photon numbers of single-photon pulse signals entering the first single-photon detector and the second single-photon detector respectively;
s204: according to the coincidence counting principle, the photon counting results output by the first single-photon detector and the second single-photon detector are coincidently counted to obtain a second-order autocorrelation function output expected value of the single-photon pulse signal:
where N is 1,2,3, …, N is the maximum value of photon number contained in photon pulse, P is1 nThe probability of coincidence with the count output 1 when the photon pulse contains n photons;
and
are respectively:
outputting an expected value g according to the second-order autocorrelation function obtained in step S2042And (mu) mapping with the single photon pulse signal average photon number mu to obtain a mapping relation which accords with the counting result and the single photon pulse signal average photon number.
In the technical scheme, according to the principle of coincidence counting, if and only if two detectors have counting pulse signals to output, the coincidence counting outputs a value 1, and the other condition outputs 0; meanwhile, the working characteristics of the single-photon detector are analyzed, and the counting pulse output by the single-photon detector can be divided into three conditions, namely a photon counting pulse generated after responding to an input single-photon pulse signal, a back pulse caused by previous response and a dark counting pulse randomly generated by the single-photon detector; the first type is an effective pulse to be measured, and the second type and the third type are counting pulses generated due to the self characteristics of the single-photon detector, namely noise generated by the single-photon detector; using P1noiseAnd P2noiseThe noise generated by the two single photon detectors is measured, and meanwhile, under the condition of no external photon input, the probability of outputting counting pulses by the detectors within one-time door opening time mainly comprises dark counting noise and rear pulse noise, so that a formula (3) can be obtained; when the single photon pulse signal input into the monitoring module, namely the HBT system, only contains 0 photon, the output of the detector is only influenced by thermal noise and rear pulse, and the probability of coincidence counting output 1 is shown in a formula (5); when the single photon pulse signal input into the HBT system only contains 1 photon, the photon only enters one of the two single photon detectors, and the probability of the coincidence counting output 1 is shown in a formula (6); when the single photon pulse signal input to the HBT system contains only 2 photons, there are three cases: 2 photons all enter a first single photon detector; 1 photon enters a first single photon detector, and the other 1 photon enters a second single photon detector; 2 photons all enter a second single photon detector; therefore, the probability of coincidence with count output 1 is as shown in equation (7); from equations (5), (6) and (7), equation (8) can be derived; according to the coincidence counting principle, the photon counting results output by the first single-photon detector and the second single-photon detector are coincidently counted to obtain a second-order autocorrelation function output expected value g of the single-photon pulse signal2(mu), i.e. the sheet obtained by coincidence counting by the monitoring moduleTherefore, the relation between the average photon number mu of the single photon pulse signal and the output expected value of the second-order autocorrelation function of the single photon pulse signal can be obtained through the formula (4), the average photon number mu of the single photon pulse signal can be correspondingly obtained through the output expected value of the second-order autocorrelation function of the single photon pulse signal, the coincidence counting result and the average photon number of the single photon pulse signal are mapped, and the mapping relation between the coincidence counting result and the average photon number of the single photon pulse signal is obtained.
In conclusion, the beneficial effects of the invention are as follows:
the monitoring module of the single photon source preparation system realizes real-time monitoring on the output state of the single photon source from the photon magnitude, and utilizes the monitoring result and the pulse energy measuring result of the monitoring module to perform feedback control on the attenuation process of the optical pulse signal, thereby improving the attenuation control precision of the single photon source and stabilizing the output of the single photon source; the single photon pulse signal can reach a specific polarization state or can not reach the specific polarization state through the optical switch, and the control precision of the photon polarization state is improved according to the polarization state feedback control process. The method solves the problems that the state of the single photon pulse signal output by the single photon source cannot be monitored in real time in the prior art, and the single photon source output single photon pulse signal is unstable due to the working instability of the optical pulse signal generator and the low attenuation precision of the attenuation device.
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The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a system block diagram of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1:
as shown in fig. 1, the invention provides a single photon source preparation system, which comprises an optical pulse signal generator and an attenuation module, wherein the optical pulse signal generator outputs an optical pulse signal, and the optical pulse signal is attenuated by the attenuation module and then output;
the first beam splitting module is used for receiving the optical pulse signals output by the attenuation module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the monitoring module, and directly outputting the other path of optical pulse signals as single photon pulse signals of the system;
the monitoring module is used for receiving one path of optical pulse signals output by the first beam splitting module, performing coincidence counting on the optical pulse signals to obtain a coincidence counting result, and mapping the coincidence counting result and the average photon number of the single optical pulse signals by utilizing a mapping relation between the coincidence counting result calibrated in advance and the average photon number of the single optical pulse signals to obtain and output the average photon number information of the single optical pulse signals.
The monitoring module comprises a fourth beam splitting module, a first single-photon detector, a second single-photon detector and a data processing unit;
the fourth beam splitting module is used for receiving the optical pulse signals output by the first beam splitting module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the first single-photon detector, and outputting the other path of optical pulse signals to the second single-photon detector;
the first single-photon detector and the second single-photon detector are used for receiving the optical pulse signals output by the fourth beam splitting module, carrying out photon counting detection on the photon number in each received optical pulse signal and outputting the counting result to the data processing unit;
the data processing unit is used for receiving a first photon counting result output by the first single photon detector and a second photon counting result output by the second single photon detector, performing coincidence counting on the first photon counting result and the second photon counting result to obtain a coincidence counting result, and mapping to obtain and output average photon number information of the single photon pulse signal by using a mapping relation between the coincidence counting result and the average photon number of the single photon pulse signal, wherein the mapping relation is calibrated in advance.
The single photon source preparation system also comprises a polarization module; the polarization module comprises a light path selection module, a second beam splitting module, a polarization control module and a polarization measurement module;
the optical path selection module is used for receiving the optical pulse signal output by the optical pulse signal generator and selectively outputting the optical pulse signal to the polarization control module or selectively outputting the optical pulse signal to the attenuation module;
the polarization control module is used for receiving the optical pulse signal output by the optical path selection module, controlling the optical pulse signal to reach a specific polarization state, and outputting the optical pulse signal with the specific polarization state to the second beam splitting module;
the second beam splitting module is used for receiving the optical pulse signal output by the polarization control module, dividing the optical pulse signal into two paths, outputting one path of optical pulse signal to the polarization measurement module, and outputting the other path of optical pulse signal to the attenuation module;
the polarization measurement module receives the optical pulse signal output by the second beam splitting module, measures the optical pulse signal to obtain polarization state information of the optical pulse signal, and outputs the polarization state measurement information to the monitoring module.
The attenuation module comprises a variable attenuation module, a third beam splitting module, a light energy measuring module and a fixed attenuation module;
the variable attenuation module is used for receiving the optical pulse signal output by the optical path selection module and receiving the other optical pulse signal output by the second beam splitting module, performing variable attenuation processing on the optical pulse signal, and outputting the processed optical pulse signal to the third beam splitting module;
the third beam splitting module is used for receiving the optical pulse signals processed by the variable attenuation module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the optical energy measuring module, and outputting the other path of optical pulse signals to the fixed attenuation module;
the optical energy measuring module is used for receiving one path of optical pulse signals output by the third beam splitting module, measuring the optical energy value of the optical pulse signals and outputting the optical energy value measuring result to the monitoring module;
the fixed attenuation module is used for receiving the other path of optical pulse signal output by the third beam splitting module, performing fixed attenuation processing on the optical pulse signal, and outputting the processed optical pulse signal to the first beam splitting module.
The monitoring module is also used for receiving the polarization state measurement information output by the polarization measurement module and the light energy value measurement result output by the light energy measurement module, performing feedback control on the polarization control module according to the polarization state measurement information, and performing feedback control on the variable attenuation module according to the coincidence counting result and the light energy value measurement result.
The optical pulse signal generator adopts a pulse laser to output an initial optical pulse signal, the optical path selection module is an optical switch, the optical switch receives the initial optical pulse signal output by the pulse laser, and selectively outputs the optical pulse signal to the polarization control module or directly outputs the optical pulse signal to the attenuation module, so that the whole system can selectively generate a single-photon pulse signal with a polarization state or generate a single-photon pulse signal without the polarization state to meet the actual diversified output requirements; when the polarization control module receives the optical pulse signal output by the optical switch and controls the optical pulse signal to reach any required polarization state, the optical pulse signal with the polarization state is output to a second beam splitting module, the second beam splitting module is a second beam splitter, the second beam splitter divides the optical pulse signal into two paths according to the proportion of 10:90, 10% of the optical pulse signal is output to the polarization measurement module, and 90% of the optical pulse signal is output to the attenuation module; the polarization measurement module receives the optical pulse signal output by the second beam splitter, measures the polarization state of the optical pulse signal, and outputs the polarization state measurement information to the data processing unit in the monitoring module, the data processing unit judges whether the angle of the polarization state in the optical pulse signal is too large or too small according to the polarization state measurement information, if the angle of the polarization state in the optical pulse signal is too large, the polarization control module is subjected to polarization feedback control to reduce the angle of the polarization state, if the angle of the polarization state is too small, the polarization control module is subjected to polarization feedback control to increase the angle of the polarization state, and therefore the polarization state in the optical pulse signal is adjusted, and the control of the polarization state is more accurate and stable.
When the optical pulse signal enters the variable attenuation module through the second beam splitter or enters the variable attenuation module through the optical switch, the variable attenuation module performs variable attenuation on the energy of the optical pulse signal, so that the flexible control on the energy of the output optical pulse signal is realized; after the optical pulse signal enters a third beam splitting module through the variable attenuation module, the third beam splitting module is a third beam splitter, the third beam splitter divides the optical pulse signal into two paths according to the proportion of 99:1, 99% of the optical pulse signal is output to the optical energy measuring module, and 1% of the optical pulse signal is output to the fixed attenuation module; after the optical energy measuring module receives the optical pulse signal output by the third beam splitter, measuring the energy in the optical pulse signal, and outputting the optical energy value measuring result in the optical pulse signal to a data processing unit in the monitoring module; when the fixed attenuation module receives the optical pulse signal output by the third beam splitter, the fixed attenuation module accurately attenuates the optical pulse signal, so that the energy of the attenuated optical pulse signal reaches the single photon magnitude and is output to the first beam splitter; according to the technical scheme, after attenuation processing of the optical pulse signal is completed, the single photon magnitude optical pulse signal is obtained, photon energy is measured in proportion through the optical energy measuring module, the optical energy value measuring result is input into the data processing unit of the monitoring module, and the data processing unit performs feedback control on the variable attenuation module.
The first beam splitting module is a first beam splitter and is used for splitting an input photon pulse signal into two paths according to an equal proportion, one path of the light pulse signal is output to the monitoring module, and the monitoring module is an HBT experimental system; and taking the other path of optical pulse signal as an output end of the single photon source to output a single photon pulse signal.
The fourth beam splitting module is a fourth beam splitter; and after receiving the optical pulse signal output by the first beam splitter, the fourth beam splitter further divides the optical pulse signal into two paths according to the equal proportion, outputs one path of the optical pulse signal to the first single-photon detector, outputs the other path of the optical pulse signal to the second single-photon detector, counts and detects the photon number in the optical pulse signal through the first single-photon detector and the second single-photon detector, outputs a photon counting result to the data processing unit, performs coincidence counting operation on the counting results of the two single-photon detectors by the data processing unit, and maps and obtains and outputs the average photon number information of the single-photon pulse signal by using the mapping relation between the pre-calibrated coincidence counting result and the average photon number of the single-photon signal by using the nondetachability of photons.
Because the first beam splitter divides the optical pulse signals into two paths according to equal proportion, and the two paths of optical pulse signals are equivalent to each other, the state of the single photon pulse signal output by the other path can be represented according to the result output by the monitoring module, and the real-time monitoring of the output state of the single photon source preparation system is completed.
And moreover, the data processing unit in the monitoring module judges whether the angle of the polarization state in the optical pulse signal is too large or too small according to the polarization state measurement information, if so, the polarization control module is subjected to polarization feedback control to reduce the angle of the polarization state, if not, the polarization control module is subjected to polarization feedback control to increase the angle of the polarization state, so that the angle of the polarization state in the optical pulse signal is adjusted, the control of the polarization state is more accurate and stable, the data processing unit in the monitoring module calculates the output energy of the optical pulse signal according to a certain proportion according to the measurement result of the optical energy value, and simultaneously combines the coincidence counting result of the optical pulse signal input into the monitoring module to perform energy feedback control on the variable attenuation module, adjust the energy attenuation multiple of the optical pulse signal and ensure the stability of single-photon pulse signal output.
In the above embodiment, the calibration method calibrated in advance according to the mapping relationship between the counting result and the average photon number of the single optical pulse signal includes the following steps:
s201: the number of photons contained in each single photon pulse signal approximately follows a Poisson random process, that is, when the average number of photons contained in the output single photon pulse signal is mu, the probability of outputting the single photon pulse signal containing n photons is shown as formula (1):
wherein N is 1,2,3, …, N; n is the maximum value of the number of photons contained in the photon pulse;
s202: supposing that the single-photon pulse signal is divided into two paths after passing through a beam splitter with the beam splitting ratio of S1: S2, the two paths of single-photon pulse signal light respectively enter a first single-photon detector and a second single-photon detector, and meanwhile, the response efficiency of the first single-photon detector and the response efficiency of the second single-photon detector to the single-photon pulse signal containing n photons are eta respectively1nAnd η2nThe dark counting rates of the two single photon detectors are respectively R1darkAnd R2darkIn the case where the gating frequency is R, the probability of occurrence of dark count noise every time the door is opened is as shown in equation (2):
s203: suppose the probability of the back pulse of the first single-photon detector and the probability of the back pulse of the second single-photon detector are respectively P1spAnd P2spThe noise probability of the first single-photon detector and the noise probability of the second single-photon detector are respectively P1noiseAnd P2noiseAccording to the counting working characteristics of the single-photon detector, the following can be obtained:
wherein, mu 'and mu' are the average photon numbers of single-photon pulse signals entering the first single-photon detector and the second single-photon detector respectively;
s204: according to the coincidence counting principle, the photon counting results output by the first single-photon detector and the second single-photon detector are coincidently counted to obtain a second-order autocorrelation function output expected value of the single-photon pulse signal:
where N is 1,2,3, …, N is the maximum value of photon number contained in photon pulse, P is1 nThe probability of coincidence with the count output 1 when the photon pulse contains n photons;
and
are respectively:
outputting an expected value g according to the second-order autocorrelation function obtained in step S2042(mu) mapping with the average photon number mu of the single photon pulse signal to obtain a coincidence counting result and the single photon pulse signalAnd mapping relation of average photon number.
According to the principle of coincidence counting, if and only if two detectors have counting pulse signals to output, the coincidence counting outputs a value 1, and the rest condition outputs 0; meanwhile, the working characteristics of the single-photon detector are analyzed, and the counting pulse output by the single-photon detector can be divided into three conditions, namely a photon counting pulse generated after responding to an input single-photon pulse signal, a back pulse caused by previous response and a dark counting pulse randomly generated by the single-photon detector; the first type is an effective pulse to be measured, and the second type and the third type are counting pulses generated due to the self characteristics of the single-photon detector, namely noise generated by the single-photon detector; using P1noiseAnd P2noiseThe noise generated by the two single photon detectors is measured, and meanwhile, under the condition of no external photon input, the probability of outputting counting pulses by the detectors within one-time door opening time mainly comprises dark counting noise and rear pulse noise, so that a formula (3) can be obtained; when the single photon pulse signal input into the monitoring module, namely the HBT system, only contains 0 photon, the output of the detector is only influenced by thermal noise and rear pulse, and the probability of coincidence counting output 1 is shown in a formula (5); when the single photon pulse signal input into the HBT system only contains 1 photon, the photon only enters one of the two single photon detectors, and the probability of the coincidence counting output 1 is shown in a formula (6); when the single photon pulse signal input to the HBT system contains only 2 photons, there are three cases: 2 photons all enter a first single photon detector; 1 photon enters a first single photon detector, and the other 1 photon enters a second single photon detector; 2 photons all enter a second single photon detector; therefore, the probability of coincidence with count output 1 is as shown in equation (7); from equations (5), (6) and (7), equation (8) can be derived; according to the coincidence counting principle, the photon counting results output by the first single-photon detector and the second single-photon detector are coincidently counted to obtain a second-order autocorrelation function output expected value g of the single-photon pulse signal2(mu), that is to say the monitoring module passesThe second-order correlation function value of the single photon pulse signal obtained by coincidence counting can be obtained, therefore, the relation between the average photon number mu of the single photon pulse signal and the output expected value of the second-order autocorrelation function of the single photon pulse signal can be obtained through the formula (4), the average photon number mu of the single photon pulse signal can be correspondingly obtained through the output expected value of the second-order autocorrelation function of the single photon pulse signal, the coincidence counting result and the average photon number of the single photon pulse signal can be mapped, and the mapping relation between the coincidence counting result and the average photon number of the single photon pulse signal can be obtained.
Example 2:
the embodiment provides a single photon source preparation method, which is implemented by using the single photon source preparation system, and the method includes the steps of optical pulse signal monitoring and output, and the steps specifically include:
and according to the coincidence counting result, mapping relation between the preset calibrated coincidence counting result and the average photon number of the single-photon optical pulse signal is utilized to map and obtain the average photon number information of the single-photon optical pulse signal and output.
Before the step of monitoring and outputting the optical pulse signal, the method also comprises an optical pulse signal attenuation step, wherein the step specifically comprises the step of carrying out variable attenuation processing on the received optical pulse signal by adopting a variable attenuation module; a third beam splitting module is adopted to divide the optical pulse signals after variable attenuation processing into two paths for output; the optical energy measuring module is used for measuring the optical energy value of one path of optical pulse signals output by the third beam splitting module, and the optical energy value measuring result is output to the monitoring module; and the fixed attenuation module is adopted to perform fixed multiple attenuation processing on the other path of optical pulse signal output by the third beam splitting module and then output the optical pulse signal to the first beam splitting module.
Before the optical pulse signal attenuation step, the method further comprises the following steps:
s101: the optical pulse signal output by the optical pulse signal generator is output to the optical path selection module, and the optical pulse signal is selectively output to the polarization control module or the attenuation module;
s102: when the optical pulse signal is selected to be output to the polarization control module, the polarization control module controls the optical pulse signal to reach a specific polarization state; and the second beam splitting module is also adopted to divide the optical pulse signal with the polarization state output by the polarization control module into two paths, the polarization measurement module is adopted to measure the polarization information of one path of optical pulse signal, the polarization measurement information is output to the monitoring module, and the other path of optical pulse signal is directly transmitted to the variable attenuation module.
After the polarization measurement information is output to the monitoring module, the monitoring module performs feedback control on the polarization control module according to the polarization measurement information;
and after the optical energy value measurement result is output to the monitoring module, the monitoring module performs feedback control on the variable attenuation module according to the optical energy value measurement result and the coincidence counting result.
The calibration method of the mapping relation between the pre-calibrated coincidence counting result and the average photon number of the single-light pulse signal comprises the following steps:
s201: the number of photons contained in each single photon pulse signal approximately follows a Poisson random process, that is, when the average number of photons contained in the output single photon pulse signal is mu, the probability of outputting the single photon pulse signal containing n photons is shown as formula (1):
wherein N is 1,2,3, …, N; n is the maximum value of the number of photons contained in the photon pulse;
s202: supposing that the single-photon pulse signal is divided into two paths after passing through a beam splitter with the beam splitting ratio of S1: S2, the two paths of single-photon pulse signal light respectively enter a first single-photon detector and a second single-photon detector, and meanwhile, the response efficiency of the first single-photon detector and the response efficiency of the second single-photon detector to the single-photon pulse signal containing n photons are eta respectively1nAnd η2nTwo single photon detectionThe dark count rates of the devices are R1 respectivelydarkAnd R2darkIn the case where the gating frequency is R, the probability of occurrence of dark count noise every time the door is opened is as shown in equation (2):
s203: suppose the probability of the back pulse of the first single-photon detector and the probability of the back pulse of the second single-photon detector are respectively P1spAnd P2spThe noise probability of the first single-photon detector and the noise probability of the second single-photon detector are respectively P1noiseAnd P2noiseAccording to the counting working characteristics of the single-photon detector, the following can be obtained:
wherein, mu 'and mu' are the average photon numbers of single-photon pulse signals entering the first single-photon detector and the second single-photon detector respectively;
s204: according to the coincidence counting principle, the photon counting results output by the first single-photon detector and the second single-photon detector are coincidently counted to obtain a second-order autocorrelation function output expected value of the single-photon pulse signal:
where N is 1,2,3, …, N is the maximum value of photon number contained in photon pulse, P is1 nCoincidence of counting output for photon pulse containing n photonsProbability of out of 1;
and
are respectively:
outputting an expected value g according to the second-order autocorrelation function obtained in step S2042And (mu) mapping with the single photon pulse signal average photon number mu to obtain a mapping relation which accords with the counting result and the single photon pulse signal average photon number.
According to the invention, real-time monitoring of the output state of the single photon source is realized on the photon magnitude through the monitoring module, and the monitoring result and the pulse energy measurement result of the monitoring module are utilized to perform feedback control on the attenuation process of the optical pulse signal, so that the attenuation control precision of the single photon source is improved, and the output of the single photon source is stabilized; the single photon pulse signal can reach a specific polarization state or can not reach the specific polarization state through the optical switch, and the control precision of the photon polarization state is improved according to the polarization state feedback control process. The method solves the problems that the state of the single photon pulse signal output by the single photon source cannot be monitored in real time in the prior art, and the single photon source output single photon pulse signal is unstable due to the working instability of the optical pulse signal generator and the low attenuation precision of the attenuation device.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (8)
1. A single photon source preparation system comprises an optical pulse signal generator and an attenuation module, wherein the optical pulse signal generator outputs an optical pulse signal, and the optical pulse signal is output after being attenuated by the attenuation module;
the first beam splitting module is used for receiving the optical pulse signals output by the attenuation module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the monitoring module, and directly outputting the other path of optical pulse signals as single photon pulse signals of the system;
the monitoring module is used for receiving one path of optical pulse signals output by the first beam splitting module, performing coincidence counting on the optical pulse signals to obtain a coincidence counting result, and mapping the coincidence counting result and the average photon number of the single optical pulse signals by utilizing a mapping relation between a pre-calibrated coincidence counting result and the average photon number of the single optical pulse signals to obtain and output average photon number information of the single optical pulse signals;
the monitoring module comprises a fourth beam splitting module, a first single-photon detector, a second single-photon detector and a data processing unit;
the fourth beam splitting module is used for receiving the optical pulse signals output by the first beam splitting module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the first single-photon detector, and outputting the other path of optical pulse signals to the second single-photon detector;
the first single-photon detector and the second single-photon detector are used for receiving the optical pulse signals output by the fourth beam splitting module, carrying out photon counting detection on the respective received optical pulse signals and outputting counting results to the data processing unit;
the data processing unit is used for receiving a first photon counting result output by the first single-photon detector and a second photon counting result output by the second single-photon detector, performing coincidence counting on the first photon counting result and the second photon counting result to obtain a coincidence counting result, and mapping to obtain and output average photon number information of the single-photon pulse signal by using a mapping relation between the coincidence counting result and the average photon number of the single-photon pulse signal, which is calibrated in advance;
the device also comprises a polarization module; the polarization module comprises a light path selection module, a second beam splitting module, a polarization control module and a polarization measurement module;
the optical path selection module is used for receiving the optical pulse signal output by the optical pulse signal generator and selectively outputting the optical pulse signal to the polarization control module or selectively outputting the optical pulse signal to the attenuation module;
the polarization control module is used for receiving the optical pulse signal output by the optical path selection module, controlling the optical pulse signal to reach a specific polarization state, and outputting the optical pulse signal with the specific polarization state to the second beam splitting module;
the second beam splitting module is used for receiving the optical pulse signal output by the polarization control module, dividing the optical pulse signal into two paths, outputting one path of optical pulse signal to the polarization measurement module, and outputting the other path of optical pulse signal to the attenuation module;
the polarization measurement module receives the optical pulse signal output by the second beam splitting module, measures the optical pulse signal to obtain polarization state information of the optical pulse signal, and outputs the polarization state measurement information to the monitoring module.
2. A single photon source production system as in claim 1 wherein said attenuation module comprises a variable attenuation module, a third beam splitting module, an optical energy measurement module and a fixed attenuation module;
the variable attenuation module is used for receiving the optical pulse signal output by the optical path selection module and receiving the other optical pulse signal output by the second beam splitting module, performing variable attenuation processing on the optical pulse signal, and outputting the processed optical pulse signal to the third beam splitting module;
the third beam splitting module is used for receiving the optical pulse signals processed by the variable attenuation module, dividing the optical pulse signals into two paths, outputting one path of optical pulse signals to the optical energy measuring module, and outputting the other path of optical pulse signals to the fixed attenuation module;
the optical energy measuring module is used for receiving one path of optical pulse signals output by the third beam splitting module, measuring the optical energy value of the optical pulse signals and outputting the optical energy value measuring result to the monitoring module;
the fixed attenuation module is used for receiving the other path of optical pulse signal output by the third beam splitting module, performing fixed attenuation processing on the optical pulse signal, and outputting the processed optical pulse signal to the first beam splitting module.
3. The single photon source production system as claimed in claim 2, wherein the monitoring module is further configured to receive polarization state measurement information output from the polarization measurement module and optical energy measurement results output from the optical energy measurement module, perform feedback control on the polarization control module according to the polarization state measurement information, and perform feedback control on the variable attenuation module according to the coincidence count result and the optical energy measurement results.
4. A single photon source preparation method, characterized in that the preparation is carried out by using the single photon source preparation system as claimed in any one of claims 1 to 3, the method comprises the steps of optical pulse signal monitoring and output, and the steps are as follows:
and according to the coincidence counting result, mapping relation between the preset calibrated coincidence counting result and the average photon number of the single-photon optical pulse signal is utilized to map and obtain the average photon number information of the single-photon optical pulse signal and output.
5. The method for preparing a single photon source according to claim 4, further comprising an optical pulse signal attenuation step before the optical pulse signal monitoring and outputting step, wherein the optical pulse signal attenuation step is to perform variable attenuation processing on the received optical pulse signal by using a variable attenuation module; a third beam splitting module is adopted to divide the optical pulse signals after variable attenuation processing into two paths for output; the optical energy measuring module is used for measuring the optical energy value of one path of optical pulse signals output by the third beam splitting module, and the optical energy value measuring result is output to the monitoring module; and the fixed attenuation module is adopted to perform fixed multiple attenuation processing on the other path of optical pulse signal output by the third beam splitting module and then output the optical pulse signal to the first beam splitting module.
6. A method for preparing a single photon source as in claim 5 further comprising the steps of, prior to the step of attenuating the optical pulse signal:
s101: the optical pulse signal output by the optical pulse signal generator is output to the optical path selection module, and the optical pulse signal is selectively output to the polarization control module or the attenuation module;
s102: when the optical pulse signal is selected to be output to the polarization control module, the polarization control module controls the optical pulse signal to reach a specific polarization state; and the second beam splitting module is also adopted to divide the optical pulse signal with the polarization state output by the polarization control module into two paths, the polarization measurement module is adopted to measure the polarization information of one path of optical pulse signal, the polarization measurement information is output to the monitoring module, and the other path of optical pulse signal is directly transmitted to the variable attenuation module.
7. The method as claimed in claim 6, wherein the monitoring module performs feedback control on the polarization control module according to the polarization measurement information after outputting the polarization measurement information to the monitoring module;
and after the optical energy value measurement result is output to the monitoring module, the monitoring module performs feedback control on the variable attenuation module according to the optical energy value measurement result and the coincidence counting result.
8. The method as claimed in claim 6, wherein the calibration method based on the mapping relationship between the counting result and the average photon number of the single-light-pulse signal, which is calibrated in advance, comprises the following steps:
s201: the number of photons contained in each single photon pulse signal approximately follows a Poisson random process, that is, when the average number of photons contained in the output single photon pulse signal is mu, the probability of outputting the single photon pulse signal containing n photons is shown as formula (1):
wherein N is 1,2, 3.., N; n is the maximum value of the number of photons contained in the photon pulse;
s202: supposing that the single-photon pulse signal is divided into two paths after passing through a beam splitter with the beam splitting ratio of S1: S2, the two paths of single-photon pulse signal light respectively enter a first single-photon detector and a second single-photon detector, and meanwhile, the response efficiency of the first single-photon detector and the response efficiency of the second single-photon detector to the single-photon pulse signal containing n photons are respectively equal to that of the first single-photon detector and the second single-photon detector
And η2nThe dark counting rates of the two single photon detectors are respectively R1darkAnd R2darkIn the case where the gating frequency is R, the probability of occurrence of dark count noise every time the door is opened is as shown in equation (2):
s203: suppose the probability of the back pulse of the first single-photon detector and the probability of the back pulse of the second single-photon detector are respectively P1spAnd P2spThe noise probability of the first single-photon detector and the noise probability of the second single-photon detector are respectively P1noiseAnd P2noiseAccording to the counting working characteristics of the single-photon detector, the following can be obtained:
P2noise＝P2sp∑[(P(μ″，n))η2n+P2dark] (3)
wherein, mu 'and mu' are the average photon number of single-photon pulse signals entering the first single-photon detector and the second single-photon detector respectively;
s204: according to the coincidence counting principle, the photon counting results output by the first single-photon detector and the second single-photon detector are coincidently counted to obtain a second-order autocorrelation function output expected value of the single-photon pulse signal:
wherein N is 1,2,3, N is the maximum value of the number of photons contained in the photon pulse,
the probability of coincidence with the count output 1 when the photon pulse contains n photons;
and
are respectively:
outputting an expected value g according to the second-order autocorrelation function obtained in step S2042And (mu) mapping with the single photon pulse signal average photon number mu to obtain a mapping relation which accords with the counting result and the single photon pulse signal average photon number.
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