High-precision quantum distance measurement device and method based on frequency entangled state

Abstract

The invention relates to the field of quantum measurement technology, and provides a high-precision quantum distance measurement device and method based on frequency entangled state, comprising an entangled photon source, a polarization beam splitter, a single-mode optical fiber coupler group, an optical fiber circulator and an optical transceiver antenna; the entangled photon source comprises a pump light source, a first lens, a nonlinear optical crystal, a temperature control furnace, a temperature control module, a second lens, a dichroic mirror and a long-pass filter; the third port of the polarization beam splitter is connected with a reflector, the reflector is connected with a second single-mode optical fiber coupler, and the second single-mode optical fiber coupler is connected with a second single-photon detector; the second port of the polarization beam splitter is connected with a first single-mode optical fiber coupler, the first single-mode optical fiber coupler is connected with an optical fiber circulator, one end of the optical fiber circulator is connected with an optical transceiver antenna, and the other end of the optical fiber circulator is connected with the first single-photon detector; the invention has the advantages of large range and high-precision distance measurement, and can better complete the distance measurement.

Description

Technical Field

[0001] The present invention relates to the field of quantum measurement technology, and in particular to a high-precision quantum distance measurement device and method based on frequency entangled states. Background Art

[0002] Distance measurement technology is the core technology for achieving unknown target positioning and navigation, and plays an important role in mobile communications and aerospace. With the development of related applications, people's requirements for the accuracy of distance measurement technology are getting higher and higher.

[0003] Traditional ranging technology usually uses light pulses to send and receive light signals, and determines the distance by measuring the flight time of the light signal. However, in this technology, the measurement accuracy is limited by several factors, including the measurement accuracy of the light pulse and the shot noise of the laser. First, the measurement accuracy of the light pulse refers to the ability of the measuring device to accurately determine the time of the light pulse in the process of measuring the light pulse reaching the target and returning. The determination of this time is affected by the performance of the measuring device itself and environmental factors, such as temperature changes, mechanical vibrations, etc. Therefore, even the most advanced measuring equipment has a certain measurement error. Secondly, the shot noise of the laser is also one of the factors affecting the ranging accuracy. In the laser, the emission of photons is not completely regular, and there will be a certain uncertainty, which is shot noise. This noise will cause small fluctuations in the frequency or phase of the laser, thereby affecting the accuracy of the measurement results. These factors together lead to the limitation of ranging accuracy, which is called the Standard Quantum Limit (SQL). SQL refers to the minimum ranging accuracy determined by laser shot noise under the conditions of classical light. However, the use of entangled light sources can break through the quasi-quantum limit. A frequency-time entangled light source is a special light source that can produce two photons that are highly correlated in frequency and time. There is quantum entanglement between these two photons, that is, the state of one photon is closely related to the state of the other photon. By utilizing the properties of this quantum entanglement, ranging accuracy beyond SQL can be achieved. Because the two photons generated by the frequency-time entangled light source have special coherence properties, they can offset part of the errors caused by the optical pulse measurement accuracy and laser shot noise, thereby improving the ranging accuracy. Therefore, quantum ranging using frequency-time entangled light sources and Hong-Ou-Mandel (HOM) interference has emerged. This is a method that uses the interference effect of quantum entangled two photons to achieve high-precision ranging. Although this method has potential, there are also some problems and challenges:

[0004] 1) Stability of interferometer: HOM interferometer can improve the ranging accuracy by using the frequency entanglement property, but the interferometer inevitably has instability, which will increase the measurement error.

[0005] 2) Inability to perform long-distance ranging: To achieve HOM interferometric ranging, the signal photons and idler photons need to arrive at the beam splitter at the same time. In practical applications, the time domain width of both signal photons and idler photons is limited. When using long-distance ranging, the reference photons left locally cannot achieve long-distance delay, and thus cannot achieve effective HOM interferometric ranging.

[0006] 3) Experimental complexity and cost: The realization of HOM interferometry experiments requires complex optical equipment and experimental arrangements, as well as a highly stable experimental environment. The construction and maintenance costs of these equipment and environments may be high, limiting the scope of application of this technology. Summary of the invention

[0007] The present invention provides a high-precision quantum distance measurement device and method based on frequency entangled state, which can overcome certain or some defects of the prior art.

[0008] A high-precision quantum distance measurement device based on frequency entangled states according to the present invention comprises an entangled photon source, a polarization beam splitter, a single-mode optical fiber coupler group, an optical fiber circulator and an optical transceiver antenna;

[0009] The entangled photon source comprises a pump light source, a first lens, a nonlinear optical crystal, a temperature control furnace, a temperature control module, a second lens, a dichroic mirror, and a long-pass filter; the entangled photon source is used to obtain a frequency-entangled two-photon state, and the two-photon state has an extremely wide distribution in the frequency difference direction, that is, the two-photon state has an extremely narrow distribution in the time difference direction;

[0010] The single-mode optical fiber coupler group includes a first single-mode optical fiber coupler and a second single-mode optical fiber coupler;

[0011] The polarization beam splitter has three ports, two photons are input through the first port, signal photons and idler photons are separated through the polarization beam splitter, signal photons are output through the second port, idler photons are output through the third port, the third port is connected to a reflector, the reflector is connected to a second single-mode fiber coupler, the second single-mode fiber coupler is electrically connected to a second single-photon detector; the second port is connected to a first single-mode fiber coupler, the first single-mode fiber coupler is connected to a fiber circulator, one end of the fiber circulator is connected to an optical transceiver antenna, and the other end of the fiber circulator is electrically connected to the first single-photon detector; the first single-photon detector and the second single-photon detector are both connected to a coincidence counter, and the coincidence counter is connected to a computer end.

[0012] Preferably, the pump light generated by the pump light source is focused onto the nonlinear optical crystal through the first lens, and the temperature of the crystal is adjusted by controlling the temperature control furnace through the temperature control module, so that the pump light undergoes spontaneous parametric down conversion (SPDC) in the crystal, and the generated two photons and the remaining pump light are collimated by the second lens; a dichroic mirror is placed at 45° to reflect the pump light and transmit the two photons, and a long-pass filter is used to further filter out the remaining pump light in the two photons, so that the obtained two photons have an extremely wide distribution in the frequency difference direction, that is, the two photons have an extremely narrow distribution in the time difference direction.

[0013] Preferably, the idle frequency photons are incident on the second single-mode optical fiber coupler via a reflector and are collected by the second single-photon detector after being transmitted through the optical fiber.

[0014] Preferably, the signal photons are incident on the first single-mode fiber coupler, transmitted via the optical fiber to the optical fiber circulator, output from the optical fiber circulator and then incident on the optical transceiver antenna, which sends the signal photons to the free space, so that the signal photons propagate to the target to be measured; the signal photons reflected by the target to be measured are returned and collected by the optical transceiver antenna, transmitted via the optical fiber to the optical fiber circulator, and the signal photons output from the optical fiber circulator are collected by the first single-photon detector after being transmitted via the optical fiber.

[0015] Preferably, the single-photon detection signals generated by the first single-photon detector and the second single-photon detector are incident on a coincidence counter to realize coincidence counting measurement of signal photons and idler photons, and the coincidence counting measurement results are processed on a computer according to the time of flight (TOF) ranging principle to obtain distance information of the target to be measured.

[0016] The present invention also provides a high-precision quantum distance measurement method based on frequency entangled states, which adopts the above-mentioned high-precision quantum distance measurement device based on frequency entangled states and includes the following steps:

[0017] S1. Obtaining double photons through a pump light source, a first lens, a nonlinear optical crystal, a temperature control furnace, a temperature control module, a second lens, a dichroic mirror, and a long-pass filter. The double photons have an extremely wide distribution in the frequency difference direction, that is, the double photons have an extremely narrow distribution in the time difference direction;

[0018] S2. The two photons are a pair of entangled photons, called signal photons and idler photons. After being separated by a polarization beam splitter, the idler photons are coupled into the second single-photon detector through a reflector. The reflector is adjusted to maximize the single count observed on the computer side. The signal photons are also coupled into the first single-photon detector to maximize the single count observed on the computer side.

[0019] S3. Record the relevant data of the peak of coincidence count when the coincidence count is the largest;

[0020] S4. Repeat S3 multiple times to obtain repeated measurement data, and process the data to obtain ranging information;

[0021] Preferably, in the two-photon case, the frequency difference Big enough, and represent the angular frequencies of the signal photon and the idler photon respectively. According to the Fourier transform principle, the time-bandwidth product is a constant, that is:

[0022] ;

[0023] in, and are the arrival times of the signal photon and the idler photon at the detector, is the time difference between the signal photon and the idler photon, so when the frequency difference When it is big enough, Small enough.

[0024] Preferably, in S2-S4, the ranging principle is:

[0025] The idler photon is directly coupled and received by the second single-photon detector as a reference signal; the signal photon is first transmitted to the target to be measured through the optical fiber circulator and the optical transceiver antenna as a measurement signal, and then reflected by the optical fiber circulator and the optical transceiver antenna and received by the first single-photon detector;

[0026] Assume that the arrival time of the signal photon and the idler photon at the detector is and , the speed of light is c , distance to be measured L is the distance from the light source to the target to be measured .

[0027] The beneficial effects of the present invention are as follows:

[0028] 1) Improve the ranging accuracy and ranging range: Traditional ranging technology is difficult to achieve high-precision distance measurement. The use of frequency entangled HOM interferometer ranging can improve the accuracy, but this technology cannot achieve long-range measurement. The present invention designs a frequency entangled quantum light source so that its two photons have a very wide distribution in the frequency difference direction, that is, the distribution of two photons in the time difference direction is extremely narrow. By combining this time correlation characteristic with the time-of-flight technology, long-distance ranging can be achieved while improving the ranging accuracy.

[0029] 2) Breaking through the quantum limit: By using an entangled light source instead of a classical coherent light source, time-of-flight quantum ranging can break through the quantum limit of classical light ranging, namely the standard quantum limit (SQL), and can improve ranging accuracy by breaking through the quantum limit. By utilizing the characteristics of time-of-flight technology and quantum entangled light source technology, higher measurement accuracy can be achieved than traditional methods, especially when measuring long distances.

[0030] 3) Coping with complex environments: Compared with HOM interferometric ranging technology, time-of-flight quantum ranging technology has a stronger ability to resist environmental noise and interference, and can achieve stable ranging performance in complex environments. This makes the technology widely applicable in various application scenarios, including outdoor environments, atmospheric interference, stray light pollution, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the principle diagram of high-precision quantum distance measurement based on frequency entangled states;

[0032] Figure 2 This is the principle diagram of frequency entanglement Fourier transform;

[0033] Figure 3 Schematic diagram of different correlated two-photons;

[0034] Figure 4 This is a diagram of the Joint Spectral Intensity experimental setup;

[0035] Figure 5 Schematic diagram of the joint spectrum of two photons in Example 1;

[0036] Figure 6 This is a schematic diagram of the projection direction of the signal light in Example 1;

[0037] Figure 7 This is a schematic diagram of the idler light direction projection in Example 1;

[0038] Figure 8 This is a schematic diagram of the anti-diagonal projection in Example 1;

[0039] Fig. 9 This is a linear graph of the center position of the peak that matches the count in Example 1;

[0040] Fig.10 This is the peak fitting diagram that matches the count in Example 1;

[0041] Fig.11 Schematic diagram of the joint spectrum of two photons in Example 2. DETAILED DESCRIPTION

[0042] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0043] like Figure 1 As shown, this embodiment provides a high-precision quantum distance measurement device based on frequency entangled state, which includes an entangled photon source, a polarization beam splitter 9, a single-mode fiber coupler group, a fiber circulator 11 and an optical transceiver antenna 12;

[0044] The entangled photon source comprises a pump light source 1, a first lens 2, a nonlinear optical crystal 3, a temperature control furnace 4, a temperature control module 5, a second lens 6, a dichroic mirror 7, and a long-pass filter 8; the entangled photon source is used to obtain two photons, and the two photons have an extremely wide distribution in the frequency difference direction, that is, the two photons have an extremely narrow distribution in the time difference direction;

[0045] The single-mode optical fiber coupler group includes a first single-mode optical fiber coupler 10 and a second single-mode optical fiber coupler 15;

[0046] The polarization beam splitter 9 (PBS) has three ports. Two photons are input through the first port, and signal photons and idler photons are separated through the polarization beam splitter 9. The signal photons are output through the second port, and the idler photons are output through the third port. The third port is connected to a reflector 14, and the reflector 14 is connected to a second single-mode fiber coupler 15. The second single-mode fiber coupler 15 is electrically connected to a second single-photon detector 16; the second port is connected to a first single-mode fiber coupler 10, and the first single-mode fiber coupler 10 is connected to a fiber circulator 11. One end of the fiber circulator 11 is connected to an optical transceiver antenna 12, and the other end of the fiber circulator 11 is electrically connected to a first single-photon detector 13; the first single-photon detector 13 and the second single-photon detector 16 are both connected to a coincidence counter 17, and the coincidence counter 17 is connected to a computer terminal 18.

[0047] The pump light generated by the pump light source 1 is focused onto the nonlinear optical crystal 3 through the first lens 2. The temperature control furnace 4 is controlled by the temperature control module 5 to adjust the crystal temperature, so that the pump light undergoes spontaneous parametric down conversion (SPDC) in the crystal. The generated two photons and the remaining pump light are collimated by the second lens 6. The dichroic mirrors 7 (DM) are placed at 45° to reflect the pump light and transmit the two photons. The long pass filter 8 (LPF) is used to further filter out the remaining pump light in the two photons. The obtained two photons have an extremely wide distribution in the frequency difference direction, that is, the two photons have an extremely narrow distribution in the time difference direction.

[0048] The idler photons are incident on the second single-mode fiber coupler 15 via the reflector 14 and are collected by the second single-photon detector 16 after being transmitted through the optical fiber.

[0049] The signal photon is incident on the first single-mode fiber coupler 10, transmitted through the optical fiber to the optical fiber circulator 11, and then output from the optical fiber circulator 11 and incident on the optical transceiver antenna 12. The optical transceiver antenna 12 sends the signal photon to the free space, so that the signal photon propagates to the target to be measured; the signal photon reflected by the target to be measured is collected by the optical transceiver antenna 12 after returning, and enters the optical fiber circulator 11 through the optical fiber transmission. The signal photon output from the optical fiber circulator 11 is collected by the first single-photon detector 13 after being transmitted through the optical fiber.

[0050] The single photon detection signals generated by the first single photon detector 13 and the second single photon detector 16 are incident on the coincidence counter 17 to realize the coincidence counting measurement of the signal photons and the idler photons. The coincidence counting measurement results are processed by the computer terminal 18 according to the time-of-flight ranging principle to obtain the distance information of the target to be measured.

[0051] This embodiment provides a high-precision quantum distance measurement method based on frequency entangled states, which adopts the above-mentioned high-precision quantum distance measurement device based on frequency entangled states and includes the following steps:

[0052] S1. Obtaining double photons through a pump light source 1, a first lens 2, a nonlinear optical crystal 3, a temperature control furnace 4, a temperature control module 5, a second lens 6, a dichroic mirror 7, and a long-pass filter 8. The double photons have an extremely wide distribution in the frequency difference direction, that is, the double photons have an extremely narrow distribution in the time difference direction;

[0053] S2. The two photons are a pair of entangled photons, respectively called signal photons and idler photons. After being separated by the polarization beam splitter 9, the idler photons are coupled into the second single-photon detector 16 through the reflector 14. The reflector 14 is adjusted so that the single count observed at the computer end is maximized; the signal photons are also coupled into the first single-photon detector 13 so that the single count observed at the computer end is maximized;

[0054] S3. Record the relevant data of the peak of coincidence count when the coincidence count is the largest;

[0055] S4. Repeat S3 multiple times to obtain multiple repeated measurement data, and process the data to obtain ranging information.

[0056] When the two photons of the frequency entangled quantum light source have a very wide distribution in the frequency difference direction, such as Figure 2 As shown in part (a), according to the Fourier transform principle of the two-photon wave packet, the distribution of the two photons in the time difference direction is extremely narrow, as shown in Figure 2In contrast, the distribution of the two photons in the time difference direction is extremely wide. Big enough, and represent the angular frequencies of the signal photon and the idler photon respectively. According to the Fourier transform principle, there exists:

[0057] ;

[0058] in, and are the arrival times of the signal photon and the idler photon at the detector, is the time difference between the signal photon and the idler photon, so when the frequency difference When it is big enough, Small enough, and The value of is the value required for distance measurement.

[0059] like Figure 3 As shown in the figure, the Fourier transform of the theoretical simulation of the two-photon joint spectrum is shown in the figure. The projection in the direction is very narrow, so after Fourier transform The directional projection is very wide. In order to achieve high-precision ranging, it is necessary to obtain a very small , then a wide spectrum of two photons is required. At the same time, by comparing the uncorrelated photons with the frequency domain anti-correlation, it can be found that the frequency domain anti-correlation is extremely narrow in the time domain distribution. Therefore, this embodiment designs a frequency entangled quantum light source so that its two photons have a very wide distribution in the frequency difference direction, that is, the distribution of two photons in the time difference direction is extremely narrow. Utilizing this time correlation characteristic combined with two-photon interference is expected to greatly improve the ranging accuracy.

[0060] In S2-S4, the ranging principle is:

[0061] The idle photon is directly coupled and received by the second single-photon detector 16 as a reference signal; the signal photon is first transmitted to the target to be measured through the optical fiber circulator 11 and the optical transceiver antenna 12 as a measurement signal, and then reflected by the optical fiber circulator 11 and the optical transceiver antenna 12 and coupled and received by the first single-photon detector 13;

[0062] Assume that the arrival time of the signal photon and the idler photon at the detector is and , the speed of light is c , distance to be measured L is the distance from the light source to the target to be measured:

[0063] Example 1

[0064] The frequency entangled two-photon state with a central wavelength of 810 nm is used. Table 1 shows the relevant theoretical simulation results. The first column shows the frequency entangled two-photon state in the frequency domain anti-diagonal The half-height full width of the wavelength corresponding to the directional projection; the second column is its anti-diagonal in the time domain The third column is the relative distance obtained by multiplying the second column by the speed of light.

[0065] Table 1: Theoretical simulation results of 810nm entangled two-photon

[0066]

[0067] 810nm experimental device diagram Figure 1As shown, the 810nm light generated by the Mira900 titanium sapphire laser (repetition frequency 76MHz) is frequency-doubled to generate a 405nm light source as a pump light source 1, and is focused onto a nonlinear optical crystal 3 through a first lens 2. The nonlinear optical crystal 3 is a periodically polarized potassium titanyl phosphate (PPKTP) crystal (polarization period is 9.825um, 1×2×10mm, Type-II). The temperature control furnace 4 is controlled by a temperature control module 5 to adjust the crystal temperature to generate spontaneous parametric down conversion SPDC, and then collimated by a second lens 6. The focal lengths of the first lens 2 and the second lens 6 are both 100mm. A dichroic mirror 7 (DM) is placed at 45° to reflect the pump light and transmit the two-photon light. A long pass filter 8 (LPF) is used to further filter out the remaining pump light in the two-photon light to ensure the spectral purity of the two-photon light. The obtained two photons have an extremely wide distribution in the frequency difference direction, that is, the two photons have an extremely narrow distribution in the time difference direction. The signal photons and idler photons in the two photons are separated by the polarization beam splitter 9 (PBS), and the idler photons are incident on the second single-mode fiber coupler 15 through the reflector 14, and are collected by the second single-photon detector 16 after being transmitted through the optical fiber. The signal photons are incident on the first single-mode fiber coupler 10, transmitted into the optical fiber circulator 11 through the optical fiber, and then output from the optical fiber circulator 11 and incident on the optical transceiver antenna 12. The optical transceiver antenna 12 sends the signal photons to the free space, so that they propagate to the target to be measured. The target to be measured is replaced by a reflector (mirror) placed on the stepper motor. The signal photons reflected by the reflector (mirror) are collected by the optical transceiver antenna 12 after returning, and enter the optical fiber circulator 11 through the optical fiber transmission. The signal photons output from the optical fiber circulator 11 are collected by the first single-photon detector 13 after being transmitted through the optical fiber. The single photon detection signals generated by the first single photon detector 13 and the second single photon detector 16 are incident on the coincidence counter 17 to realize the coincidence counting measurement of the signal photon and the idler photon. According to the time-of-flight ranging principle, the coincidence counting measurement result can be processed by the computer terminal 18 to obtain the distance information of the target to be measured. The position of the stepper motor is changed to simulate different distances to be measured, and different coincidence counting measurement results are recorded to obtain the distance to be measured.

[0068] Joint Spectrum Intesity Measurement

[0069] like Figure 4 The device diagram shown does not include parts that are Figure 1The pump light signal is connected to the coincidence counter 17, and the signal light and idler light generated in the experiment enter the first single-photon detector 13 and the second single-photon detector 16 respectively. The electrical signals input by the two single-photon detectors and the electrical signal of the pump light itself are measured together for the joint spectrum distribution. Through the experimentally measured data, the joint spectrum (JSI) of the two photons actually generated by the 10mm type II PPKTP in this experiment is plotted as follows: Figure 5 As shown, the signal photon wavelength, idler photon wavelength and anti-diagonal projection are respectively performed to calculate the corresponding half-height full width, as shown in Figure 6 , Figure 7 and Figure 8 As shown. is the wavelength of the signal photon, is the wavelength of the idler photon, and wavelength is the wavelength. Figure 6 The full width at half maximum (FWHM) obtained by fitting the medium signal photons is 21.8nm; Figure 7 The full width at half maximum (FWHM) obtained by fitting the intermediate idler photons is 31.5nm; Figure 8 The full width at half maximum (FWHM) obtained by fitting the mid-anti-diagonal line is as high as 36.2nm, indicating that an entangled light source with an extremely wide spectrum has been prepared.

[0070] TOF measurement data processing

[0071] Different coincident counting peaks are obtained by experimental measurement at different test distances, and the coincident counting peaks are fitted to obtain their center positions. Fig. 9 The middle dot is the center position of the peak of coincidence counts at different distances to be measured. The straight line is the theoretical expectation. Fig. 9 It can be seen that the experimental data is highly consistent with the theory, which shows that the device can realize TOF ranging and the ranging range is large enough.

[0072] Repeat the measurement of the coincident count peaks at the same distance to be measured for many times, select two distances to be measured to measure 5 groups of data, and then fit the 5 groups of coincident count peaks. Fig.10 To measure the coincidence count data and the fitting curve, the horizontal axis is the electrical delay between the signal photon and the idler photon, and its unit is bin, which is the time resolution of the coincidence counter; the vertical axis is the coincidence count. Fig.10 The middle dots are the coincident counting peak data obtained from the experiment. The curve is a Gaussian fit. a1-a5 are 5 sets of data at the distance 1 to be measured, and b1-b5 are 5 sets of data at the distance 2 to be measured.

[0073] Table 2 and Table 3 respectively record the center position, half-height full width, and coincidence count of the fitted coincidence count peak at the test distance 1 and the test distance 2:

[0074] Table 2: Key features of the peaks with the counts after fitting at the measured distance 1

[0075]

[0076] It can be seen from the table above that the average value of the center position of the peak count at the measured distance 1 is:

[0077]

[0078] The variance is:

[0079]

[0080] The standard deviation is:

[0081]

[0082] According to 1bin=128ps and the speed of light The measurement accuracy can be obtained as:

[0083]

[0084] Table 3: Key features of the peaks with the counts after fitting at the measured distance 2

[0085]

[0086] It can be seen from the table above that the average value of the center position of the counting peak at the measured distance 2 is:

[0087]

[0088] The variance is:

[0089]

[0090] The standard deviation is:

[0091]

[0092] According to 1bin=128ps and the speed of light The measurement accuracy can be obtained as:

[0093]

[0094] It can be seen from the above experimental data that the measurement results of the two measurement positions have an accuracy of sub-millimeter level, so this scheme can achieve high-precision measurement.

[0095] Example 2

[0096] The frequency entangled two-photon state with a central wavelength of 1550nm is used. Table 4 shows the relevant theoretical simulation results. The first column shows the frequency entangled two-photon state in the frequency domain anti-diagonal The half-height full width of the wavelength corresponding to the directional projection; the second column is its anti-diagonal in the time domain The third column is the relative distance obtained by multiplying the second column by the speed of light.

[0097] Table 4: Theoretical simulation results of 1550nm entangled two-photon

[0098]

[0099] Based on similar Figure 1 The experimental device uses 792nm pump light to pump the type II periodically polarized lithium tantalate (PPSLT) crystal to generate frequency entangled two photons with a central wavelength of 1584nm to perform the same JSI measurement experiment. The joint spectrum of the two photons (JSI) is plotted through the experimentally measured data, as shown in the figure. Fig.11 shown.

[0100] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A high-precision quantum distance measurement device based on frequency entangled states, characterized in that: It comprises an entangled photon source, a polarization beam splitter (9), a single-mode optical fiber coupler group, an optical fiber circulator (11) and an optical transceiver antenna (12); The entangled photon source comprises a pump light source (1), a first lens (2), a nonlinear optical crystal (3), a temperature control furnace (4), a temperature control module (5), a second lens (6), a dichroic mirror (7), and a long-pass filter (8); the entangled photon source is used to obtain two photons, and the two photons have an extremely wide distribution in the frequency difference direction, that is, the two photons have an extremely narrow distribution in the time difference direction; The single-mode optical fiber coupler group comprises a first single-mode optical fiber coupler (10) and a second single-mode optical fiber coupler (15); The polarization beam splitter (9) has three ports. Two photons are input through the first port. Signal photons and idler photons are separated through the polarization beam splitter (9). Signal photons are output through the second port. Idler photons are output through the third port. The third port is connected to a reflector (14). The reflector (14) is connected to a second single-mode optical fiber coupler (15). The second single-mode optical fiber coupler (15) is electrically connected to a second single-photon detector (16). The second port is connected to a first single-mode optical fiber coupler (10). The first single-mode optical fiber coupler (10) is connected to an optical fiber circulator (11). One end of the optical fiber circulator (11) is connected to an optical transceiver antenna (12). The other end of the optical fiber circulator (11) is electrically connected to a first single-photon detector (13). The first single-photon detector (13) and the second single-photon detector (16) are both connected to a coincidence counter (17). The coincidence counter (17) is connected to a computer terminal (18).

2. The high-precision quantum distance measurement device based on frequency entangled state according to claim 1, characterized in that: The pump light generated by the pump light source (1) is focused onto a nonlinear optical crystal (3) through a first lens (2), and the crystal temperature is adjusted by controlling a temperature control furnace (4) through a temperature control module (5), so that the pump light undergoes spontaneous parametric down conversion (SPDC) in the crystal, and the generated two photons and the remaining pump light are collimated through a second lens (6); a dichroic mirror (7) is placed at 45 degrees to reflect the pump light and transmit the two photons, and a long-pass filter (8) is used to further filter out the remaining pump light in the two photons, so that the obtained two photons have an extremely wide distribution in the frequency difference direction, that is, the two photons have an extremely narrow distribution in the time difference direction.

3. The high-precision quantum distance measurement device based on frequency entangled state according to claim 2, characterized in that: The idle frequency photons are incident on the second single-mode optical fiber coupler (15) via the reflector (14) and are collected by the second single-photon detector (16) after being transmitted through the optical fiber.

4. The high-precision quantum distance measurement device based on frequency entangled state according to claim 3, characterized in that: The signal photon is incident on a first single-mode optical fiber coupler (10), transmitted through an optical fiber into an optical fiber circulator (11), output from the optical fiber circulator (11) and then incident on an optical transceiver antenna (12), the optical transceiver antenna (12) sends the signal photon to free space, so that the signal photon propagates to a target to be measured; the signal photon reflected by the target to be measured is returned and collected by the optical transceiver antenna (12), transmitted through an optical fiber into the optical fiber circulator (11), and the signal photon output from the optical fiber circulator (11) is transmitted through the optical fiber and then collected by a first single-photon detector (13).

5. The high-precision quantum distance measurement device based on frequency entangled state according to claim 4, characterized in that: The single-photon detection signals generated by the first single-photon detector (13) and the second single-photon detector (16) are incident on a coincidence counter (17) to achieve coincidence counting measurement of signal photons and idler photons. The coincidence counting measurement results are processed by a computer (18) according to the time-of-flight ranging principle, thereby obtaining distance information of the target to be measured.

6. A high-precision quantum distance measurement method based on frequency entangled states, characterized in that: It adopts the high-precision quantum distance measurement device based on frequency entangled state as described in any one of claims 1 to 5, and includes the following steps: S1. A frequency entangled two-photon state is obtained by a pump light source (1), a first lens (2), a nonlinear optical crystal (3), a temperature control furnace (4), a temperature control module (5), a second lens (6), a dichroic mirror (7), and a long-pass filter (8), wherein the two-photon state has an extremely wide distribution in the frequency difference direction, that is, the two-photon state has an extremely narrow distribution in the time difference direction; S2. The two photons are a pair of entangled photons, respectively called signal photons and idler photons. After being separated by the polarization beam splitter (9), the idler photons are coupled into the second single-photon detector (16) through the reflector (14). The reflector (14) is adjusted so that the single count observed at the computer end is maximized; the signal photons are also coupled into the first single-photon detector (13) so that the single count observed at the computer end is maximized; S3. Record the relevant data of the peak of coincidence count when the coincidence count is the largest; S4. Repeat S3 multiple times to obtain multiple repeated measurement data, and process the data to obtain ranging information.

7. The high-precision quantum distance measurement method based on frequency entangled states according to claim 6, characterized in that: In two photons, the frequency difference (ω s -ω i ) is large enough, ω s and ω i Represent the angular frequencies of the signal photon and the idler photon respectively. According to the Fourier transform principle, the time-bandwidth product is a constant, that is: (ω s -ω i )(t s -t i )=Constant Among them, t s and t i are the arrival times of the signal photon and the idler photon at the detector, and (ts-ti) is the time difference between the signal photon and the idler photon. s -ω i ) is large enough, (t s -t i ) is small enough.

8. The high-precision quantum distance measurement method based on frequency entangled states according to claim 7, characterized in that: In S2-S4, the ranging principle is: The idle photon is directly coupled and received by the second single-photon detector (16) as a reference signal; the signal photon is first transmitted to the target to be measured via the optical fiber circulator (11) and the optical transceiver antenna (12) as a measurement signal, and then reflected by the optical fiber circulator (11) and the optical transceiver antenna (12) to be coupled and received by the first single-photon detector (13); Assume that the arrival time of the signal photon and the idler photon at the detector is t s and t i , the propagation speed of light is c, and the measured distance L is the distance from the light source to the target to be measured: L = c (t s -t i ) / 2.

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