Dynamic target positioning method based on quantum entanglement light correlation characteristics

Abstract

The invention provides a dynamic target positioning method based on quantum entanglement light correlation characteristics. The method comprises the following steps: firstly, generating pump light by using a semiconductor laser, irradiating the pump light to a periodically poled potassium titanyl phosphate crystal, and obtaining reference light and signal light with entanglement characteristics through a spontaneous parametric down-conversion process; then, the reference light is directly detected by a local single-photon detector, the signal light is sent to a to-be-detected area through a rotary table at different angles, the other single-photon detector is used for receiving echo photons to achieve target detection, and then a hypothesis test model is established to estimate the angle of a dynamic target; secondly, recording arrival time information of the reference light and the signal light by using a high-speed acquisition circuit, constructing a corresponding echo photon time label sequence, and performing coincidence counting on the reference light time label sequence and the signal light echo photon time label sequence by using a sliding window to obtain an entangled light second-order correlation function; taking the delay corresponding to the peak value as the flight time difference of the signal light and the reference light, calculating the distance from the light source to the target, and judging whether the target echo end photon appears or not by using the absolute median difference of the distance; and finally, obtaining an included angle between the light source and the target by using the turntable, and realizing dynamic target positioning by combining the target distance.

Description

Technical Field

[0001] The present invention belongs to the field of quantum precision measurement, and specifically relates to a method of using the correlation characteristics of quantum entangled light to achieve high-precision positioning of dynamic targets. Background Art

[0002] With the development of electronic technology, positioning systems have been widely used in all aspects of the national economy. Common positioning systems include satellite positioning systems, cellular base station positioning systems, inertial navigation positioning systems, etc., which have played an important role in the fields of smart transportation, emergency rescue, geological monitoring, etc. At present, the positioning system based on quantum entangled light is easily interfered by environmental noise, which makes it difficult to capture the target, and the number of collected echo photons is small due to the movement of the target, which leads to a decrease in positioning accuracy. In response to the above problems, the dynamic target positioning method based on the correlation characteristics of entangled light quanta proposed in the present invention will utilize the quantum fluctuation characteristics of the light field to extract entangled light quantum information with time and space correlation characteristics, thereby achieving high-precision positioning of dynamic targets. Summary of the invention

[0003] The present invention specifically comprises the following steps:

[0004] Step 1: Use a semiconductor laser with a wavelength of 405nm to generate pump light, and modulate the pump light through a 1 / 2 wave plate and a 1 / 4 wave plate to obtain linearly polarized light.

[0005] Step 2: The linearly polarized light is divided into clockwise and counterclockwise light paths through DPBS to form a Sagnac loop, and simultaneously irradiated to the PPKTP crystal to undergo spontaneous parametric down-conversion to obtain entangled light.

[0006] Step 3: The entangled light is passed through a high-pass total reflection mirror with a reflection wavelength of 405nm to reflect the excess unconverted pump light to obtain high-quality entangled light.

[0007] Step 4: Use a polarization beam splitter with a wavelength of 810nm to separate the entangled light into reference light and signal light.

[0008] Step 5: The reference light and the signal light are respectively passed through the photon coupler, that is, the reference light is directly detected by the local single-photon detector 1; the signal light is sent to the detection area at different angles through the turntable, and is detected by the single-photon detector 2 after being reflected by the target.

[0009] Step 6: Record the arrival time information of the reference light and the signal light respectively through the high-speed acquisition circuit and set different channel flags CH1 and CH2. The arrival time information of the reference light and the signal light is respectively recorded in the time tag sequence T1={t 11 ,…,t 1i ,…,t 1n} and T2={t21 ,…,t 2i ,…,t 2n}, where t ji (j=1,2; i=1,…,n) represents the i-th time tag of the j-th channel.

[0010] Step seven: perform coincidence counting on the time tag values ​​in T1 and T2, that is, take T2 as the basic sequence, and add a delay τ0 to each time tag in T1. At this time, when there is a pair of time tags belonging to T1 and T2 respectively and located within the same coincidence gate width δ0, the coincidence count value is increased by 1, so as to obtain the coarse coincidence count value n0(τ0) under the delay τ0.

[0011] Step 8: Take n0(τ0) as the input of the constant false alarm detection model, and calculate the probability P(x|H0) of the count value that matches the state H0 without a target in the detection area and the probability P(x|H1) of the count value that matches the state H1 with a target.

[0012] Step 9: Set the system's false alarm probability P fa =a, where a is a constant, and the decision threshold V of the matching count value is calculated using formula (1). T : Then, the decision threshold is: According to formula (2), when When , it is defined that there is a target in the area to be detected, and the process continues to step 10; otherwise, it is defined that there is no target in the area to be detected, and the process returns to step 5.

[0013] Step 10: When there is a target, the turntable stops rotating and uses the sliding window method to calculate the exact value of the coincidence count to obtain the accurate echo photon flight time. At the same time, it is determined whether the last photon appears in the echo photon. If so, return to step 5; otherwise, continue to step 11.

[0014] Step 11: Obtain the angle between the light source and the target according to the position where the turntable stops rotating, and realize dynamic target positioning in combination with the target distance.

[0015] The step eight comprises the following steps:

[0016] Step 8 (a): Calculate the matching result by τ j The unit is divided into M windows, and the coincidence count value in each window is recorded. The window with the maximum coincidence count value is used as the detection unit, the two adjacent windows on the left and right are used as protection units, and the other windows are used as reference units. The coincidence count values ​​of all reference units are first summed and then averaged to obtain the estimated value of the noise.

[0017] Step 8 (ii): When there is no target on the detection path, the state where only noise exists is H0. Calculate the probability that the receiving end noise and the reference photon produce a coincidence count: P I,N =exp(-N d T d ) 2 [1-exp(-ρ n τ j / T d )][1-exp(-N I )] (3) Among them, N d is the number of photons generated by the dark current of the single-photon detector, T d is the dead time of the single photon detector, N I is the number of photons received by single-photon detector 2, and N I =η q N / 2, N is the number of photon pairs emitted by the signal source, ρ n is the arrival rate of ambient noise; When there is a target on the detection path, calculate the probability of the receiving end photon and the reference photon producing a coincidence count in the H0 state: Among them, N S The light signal received by the single-photon detector 1 in the time Δt is transformed from the energy representation to the photon number representation, N n is the effective noise photon number of the whole system.

[0018] Step 8 (iii): For states H0 and H1, calculate the probability density function of the test statistic x:

[0019] The step ten comprises the following steps:

[0020] Step 10 (a): The single photon detector continuously collects data at the current angle, the window size is W, the signal light path and the reference light path are intercepted by the window size to calculate the coincidence count, and the window sliding step is s.

[0021] Step 10 (ii): Count the coincidences of the CH1 and CH2 sequences in each window. Under the condition of time delay τ, when the coincidence gate width δ is much smaller than the coherence time τ of the light field, c , that is, satisfying δ<<τ c When the count value n(τ) is consistent with the ideal second-order correlation function g (2) (τ) satisfies the following relationship: Where T is the total sampling time, δ is the coincidence gate width, R1 and R2 are the photon counting rates of single photon detectors 1 and 2, respectively, and γ1 and γ2 are the sum of the dark counting rate and the counting rate caused by the environmental noise of single photon detectors 1 and 2, respectively. i >>γ i When (i=1,2), the relationship between the normalized second-order correlation function and the coincidence count value can be simplified to:

[0022] Step 10 (III): Use the least squares method to find the discrete points (τ, g (2) (τ)) to perform curve fitting, and the horizontal coordinate τ corresponding to the peak value of the fitted curve * It is defined as the time difference between the reference light and the signal light (i.e. the echo photon flight time). At this time, the distance l from the light source to the target is:

[0023] Step 10 (IV): Calculate the distance sequence L from the light source to the target corresponding to m consecutive sliding windows = {l1,…,l m}, and construct its absolute difference sequence Y = {|l1-M L |,…,|l m -M L |}, where M L is the median of the elements in L, and also defines the median of the elements in Y M Y is the absolute median difference.

[0024] Step 10 (V): For normal distribution data, the absolute median difference divided by 0.6745 is used as the estimate of the standard deviation. For the i-th (=1,…,m) sliding window, determine whether formula (6) is satisfied. If so, it is considered that the last photon appears in the echo photon, and the target has left the current detection area, and return to step 5; otherwise, continue to step 11. Where i=1,…,m, and threshold is the defined threshold.

[0025] The step eleven comprises the following steps:

[0026] Step 11 (i): Obtain the angle θ between the light source and the target according to the position where the turntable stops rotating.

[0027] Step 11 (2): Assume that the position coordinates of the target to be located and the local access point are (x, y) and (x1, y1) respectively, and establish the following positioning equations: Solving the above equations, we can get the estimated position (x, y) of the target to be located: BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The system flow chart of the present invention is

[0029] Figure 2 The optical path structure diagram of the present invention is

[0030] Figure 3 The schematic diagram of the working timing of the high-speed acquisition circuit of the present invention is DETAILED DESCRIPTION

[0031] The implementation process of the present invention is further described in detail with reference to the accompanying drawings:

[0032] Step 1: Use a semiconductor laser with a wavelength of 405nm to generate pump light, and modulate the pump light through a 1 / 2 wave plate and a 1 / 4 wave plate to obtain linearly polarized light.

[0033] Step 2: The linearly polarized light is divided into clockwise and counterclockwise light paths through DPBS to form a Sagnac loop, and simultaneously irradiated to the PPKTP crystal to undergo spontaneous parametric down-conversion to obtain entangled light.

[0034] Step 3: The entangled light is passed through a high-pass total reflection mirror with a reflection wavelength of 405nm to reflect the excess unconverted pump light to obtain high-quality entangled light.

[0035] Step 4: Use a polarization beam splitter with a wavelength of 810nm to separate the entangled light into reference light and signal light.

[0036] Step 5: The reference light and the signal light are respectively passed through the photon coupler, that is, the reference light is directly detected by the local single-photon detector 1; the signal light is sent to the detection area at different angles through the turntable, and is detected by the single-photon detector 2 after being reflected by the target.

[0037] Step 6: Record the arrival time information of the reference light and the signal light respectively through the high-speed acquisition circuit and set different channel flags CH1 and CH2. The arrival time information of the reference light and the signal light is respectively recorded in the time tag sequence T1={t 11 ,…,t 1i ,…,t 1n} and T2={t 21 ,…,t 2i ,…,t 2n}, where t ji (j=1,2; i=1,…,n) represents the i-th time tag of the j-th channel.

[0038] Step seven: perform coincidence counting on the time tag values ​​in T1 and T2, that is, take T2 as the basic sequence, and add a delay τ0 to each time tag in T1. At this time, when there is a pair of time tags belonging to T1 and T2 respectively and located within the same coincidence gate width δ0, the coincidence count value is increased by 1, so as to obtain the coarse coincidence count value n0(τ0) under the delay τ0.

[0039] Step 8 (a): Calculate the matching result by τ j The unit is divided into 100 windows, and the coincidence count value in each window is recorded. The window with the maximum coincidence count value is used as the detection unit, the two adjacent windows on the left and right are used as protection units, and the other windows are used as reference units. The coincidence count values ​​of all reference units are first summed and then averaged to obtain the estimated value of the noise.

[0040] Step 8 (ii): When there is no target on the detection path, the state where only noise exists is H0. Calculate the probability that the receiving end noise and the reference photon produce a coincidence count: P I,N =exp(-N d T d ) 2 [1-exp(-ρ n τ j / T d )][1-exp(-N I )] (12) Among them, N d is the number of photons generated by the dark current of the single-photon detector, T d is the dead time of the single photon detector, N I is the number of photons received by single-photon detector 2, and N I =η q N / 2, N is the number of photon pairs emitted by the signal source, ρ n is the arrival rate of ambient noise; When there is a target on the detection path, calculate the probability of the receiving end photon and the reference photon producing a coincidence count in the H0 state: Among them, N S The light signal received by the single-photon detector 1 in the time Δt is transformed from the energy representation to the photon number representation, N n is the effective noise photon number of the whole system.

[0041] Step 8 (iii): For states H0 and H1, calculate the probability density function of the test statistic x:

[0042] Step 9: Set the system's false alarm probability Pfa =a, where a is a constant, and the decision threshold V of the matching count value is calculated using formula (1). T : Then, the decision threshold is: According to formula (16), when When , it is defined that there is a target in the area to be detected, and the process continues to step 10; otherwise, it is defined that there is no target in the area to be detected, and the process returns to step 5.

[0043] Step 10 (i): Set the sliding window size to 1 ms, intercept the time tag sequences collected by the reference and signal optical paths and calculate the corresponding coincidence count values, wherein the sliding step size of the window is 0.2 ms.

[0044] Step 10 (2): Step 10 (2): Count the coincidences of the CH1 and CH2 sequences in each window. Under the condition of time delay τ, when the coincidence gate width δ is much smaller than the coherence time τ of the light field, c , that is, satisfying δ<<τ c When the count value n(τ) is consistent with the ideal second-order correlation function g (2) (τ) satisfies the following relationship: Where T is the total sampling time, δ is the coincidence gate width, R1 and R2 are the photon counting rates of single photon detectors 1 and 2, respectively, and γ1 and γ2 are the sum of the dark counting rate and the counting rate caused by the environmental noise of single photon detectors 1 and 2, respectively. i >>γ i When (i=1,2), the relationship between the normalized second-order correlation function and the coincidence count value can be simplified to:

[0045] Step 10 (III): Use the least squares method to find the discrete points (τ, g (2) (τ)) to perform curve fitting, and the horizontal coordinate τ corresponding to the peak value of the fitted curve * It is defined as the time difference between the reference light and the signal light (i.e. the echo photon flight time). At this time, the distance l from the light source to the target is:

[0046] Step 10 (IV): Calculate the distance sequence L from the light source to the target corresponding to m consecutive sliding windows = {l1,…,l m}, and construct its absolute difference sequence Y = {|l1-M L |,…,|l m -M L|}, where M L is the median of the elements in L, and also defines the median of the elements in Y M Y is the absolute median difference.

[0047] Step 10 (V): For normal distribution data, the absolute median difference divided by 0.6745 is used as the estimate of the standard deviation. For the i-th (=1,…,m) sliding window, determine whether formula (6) is satisfied. If so, it is considered that the last photon appears in the echo photon, and the target has left the current detection area, and return to step 5; otherwise, continue to step 11. Where i = 1, ..., m, threshold is the defined threshold

[0048] Step 11 (i): Obtain the angle θ between the light source and the target according to the position where the turntable stops rotating.

[0049] Step 11 (2): Assume that the position coordinates of the target to be located and the local access point are (x, y) and (x1, y1) respectively, and establish the following positioning equations: Solving the above equations, we can get the estimated position (x, y) of the target to be located:

Claims

1. A dynamic target positioning method based on quantum entangled light correlation characteristics, characterized in that The following steps are involved: Step 1: Use a semiconductor laser with a wavelength of 405nm to generate pump light, and modulate the pump light through a 1 / 2 wave plate and a 1 / 4 wave plate to obtain linearly polarized light. Step 2: The linearly polarized light is divided into clockwise and counterclockwise light paths through a dual-wavelength polarizing beam splitter (DPBS) to form a Sagnac loop, and at the same time irradiated to a periodically polarized potassium titanyl phosphate (PPKTP) crystal to undergo a spontaneous parametric down-conversion process to obtain entangled light. Step 3: The entangled light is passed through a high-pass total reflection mirror with a reflection wavelength of 405nm to reflect the excess unconverted pump light to obtain high-quality entangled light. Step 4: Use a polarization beam splitter with a wavelength of 810nm to separate the entangled light into reference light and signal light. Step 5: The reference light and the signal light are respectively passed through the photon coupler, that is, the reference light is directly detected by the local single-photon detector 1; the signal light is sent to the detection area at different angles through the turntable, and is detected by the single-photon detector 2 after being reflected by the target. Step 6: Record the arrival time information of the reference light and the signal light respectively through the high-speed acquisition circuit and set different channel flags CH1 and CH2. The arrival time information of the reference light and the signal light is respectively recorded in the time tag sequence T1={t 11 ,…,t 1i ,…,t 1n } and T2={t 21 ,…,t 2i ,…,t 2n }, where t ji (j=1,2; i=1,…,n) represents the i-th time tag of the j-th channel. Step seven: perform coincidence counting on the time tag values ​​in T1 and T2, that is, take T2 as the basic sequence, and add a delay τ0 to each time tag in T1. At this time, when there is a pair of time tags belonging to T1 and T2 respectively and located within the same coincidence gate width δ0, the coincidence count value is increased by 1, so as to obtain the coarse coincidence count value n0(τ0) under the delay τ0. Step 8: Take n0(τ0) as the input of the constant false alarm detection model, and calculate the probability P(x|H0) of the count value that matches the state H0 without a target in the detection area and the probability P(x|H1) of the count value that matches the state H1 with a target. Step 9: Set the system's false alarm probability P fa =a, where a is a constant, and the decision threshold V of the matching count value is calculated using formula (1). T . Then, the decision threshold is: According to formula (2), when When , it is defined that there is a target in the area to be detected, and the process continues to step 10; otherwise, it is defined that there is no target in the area to be detected, and the process returns to step 5. Step 10: When there is a target, the turntable stops rotating and uses the sliding window method to calculate the exact value of the coincidence count to obtain the accurate echo photon flight time. At the same time, it is determined whether the last photon appears in the echo photon. If so, return to step 5; otherwise, continue to step 11. Step 11: Obtain the angle between the light source and the target according to the position where the turntable stops rotating, and realize dynamic target positioning in combination with the target distance.

2. The dynamic target positioning method based on quantum entangled light correlation characteristics according to claim 1 is characterized in that The step ten comprises the following steps: Step 10 (i): Set the sliding window size to W, intercept the time tag sequences collected by the reference and signal light paths and calculate the corresponding coincidence count values, wherein the sliding step size of the window is s. Step 10 (2): Under the condition of delay τ, when the gate width δ is much smaller than the coherence time τ of the light field c When the count value n(τ) is established, the second-order correlation function g (2) The relationship between (τ): Where T is the sampling time, R1 and R2 are the photon counting rates of single photon detectors 1 and 2, γ1 and γ2 are the sum of the dark counting rate and the counting rate caused by environmental noise of single photon detectors 1 and 2. i >>γ i When (i=1,2), the relationship between the coincidence count value and the second-order correlation function is normalized and simplified to: Step 10 (III): Use the least squares method to find the discrete points (τ, g (2) (τ)) to perform curve fitting, and the horizontal coordinate τ corresponding to the peak value of the fitted curve * It is defined as the time difference between the reference light and the signal light (i.e. the echo photon flight time). At this time, the distance l from the light source to the target is: Where c is the speed of light. Step 10 (IV): Calculate the distance sequence L from the light source to the target corresponding to m consecutive sliding windows = {l1,…,l m }, and construct its absolute difference sequence Y = {|l1-M L |,…,|l m -M L |}, where M L is the median of the elements in L, and also defines the median of the elements in Y M Y is the absolute median difference. Step 10 (V): For normal distribution data, the absolute median difference divided by 0.6745 is used as the estimate of the standard deviation. For the i-th (=1,…,m) sliding window, determine whether formula (6) is satisfied. If so, it is considered that the last photon appears in the echo photon, and the target has left the current detection area, and return to step 5; otherwise, continue to step 11. Here, threshold is a pre-given threshold.

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