Non-contact quantum radar system based on coherence enhancement

Abstract

The invention provides a coherence enhancement-based non-contact quantum radar system, which is characterized in that light emitted by a laser is divided into a first light path and a second light path through a light variable beam splitter, the first light path is converted by a first parametric conversion unit and then reaches a detection target through a first collimator, and the second light path is converted by a second parametric conversion unit; the reflected light of the detection target reaches the first optical beam splitter after passing through the second collimator; the second optical path is subjected to polarization processing of the polarization unit and conversion processing of the second parametric conversion unit in sequence, and then passes through the photon signal delay adjustment unit and the zero photon erasing device in sequence to reach the first optical beam splitter; and the second single-photon detector receives the output of the first optical beam splitter to the first optical path and the second optical path and outputs a verification result. According to the invention, coherence enhancement is realized by adopting a zero photon erasing scheme, decoupling with noise photons in the background is realized by adopting a photon interference mechanism, immunity to background noise is achieved, and the effect of non-contact imaging is greatly improved.

Description

Technical Field

[0001] The invention relates to the field of quantum radar, and in particular to a contactless quantum radar system based on coherence enhancement. Background Art

[0002] Quantum radar is a new target detection technology based on quantum entanglement and coincident quantum measurement. It has the ability to detect weak targets under strong background noise. At present, quantum radar mainly relies on the preparation of quantum entanglement and coincident quantum measurement to achieve target detection. In order to achieve coincident quantum measurement, it is necessary to achieve synchronous detection between the reference signal and the echo signal, which puts high requirements on the quantum storage of the reference signal. At present, the bandwidth of mature quantum storage is very limited, which greatly affects the actual target detection performance of quantum radar.

[0003] The present invention proposes a non-contact quantum radar system based on coherence enhancement. The system uses the coherent superposition of two quantum entanglements to obtain a signal source, and uses the path indistinguishability of quantum states to achieve target imaging, overcoming the strict limitations of common quantum radars on quantum memory. At the same time, due to the use of non-contact imaging, target imaging can be achieved under strong noise intensity, providing key support for future practical quantum radar technology. Summary of the invention

[0004] In order to solve the problems existing in the background technology, the present invention proposes a non-contact quantum radar system based on coherence enhancement.

[0005] A contactless quantum radar system based on coherence enhancement comprises a laser, an optically variable beam splitter, a detection receiving unit and a homogeneity verification unit, wherein the detection receiving unit comprises a first parameter conversion unit, a first collimator and a second collimator, and the homogeneity verification unit comprises a polarization unit, a second parameter conversion unit, a photon signal delay adjustment unit, a zero photon erasing device, a first optical beam splitter and a second single photon detector. Light emitted by the laser is divided into a first optical path and a second optical path by the optically variable beam splitter. After the first optical path is converted by the first parameter conversion unit, it passes through the first collimator and reaches a detection target. The reflected light of the detection target reaches the first optical beam splitter after passing through the second collimator. After the second optical path passes through the polarization processing of the polarization unit and the conversion processing of the second parameter conversion unit in sequence, it passes through the photon signal delay adjustment unit and the zero photon erasing device in sequence and reaches the first optical beam splitter. The second single photon detector receives the output of the first optical beam splitter to the first optical path and the second optical path and outputs a verification result.

[0006] Based on the above, it includes a feedback adjustment unit, which includes a second optical beam splitter, a first single-photon detector, a fourth single-photon detector, a third single-photon detector, a time digital converter and a signal logic processing unit. The first parameter of the first optical path converted by the first parameter conversion unit enters the first collimator, and the second parameter enters the second optical beam splitter. The third parameter of the second optical path converted by the second parameter conversion unit enters the photon signal delay adjustment unit, and the fourth parameter enters the second optical beam splitter. The first single-photon detector and the fourth single-photon detector are respectively connected to the output end of the second optical beam splitter; the auxiliary light field input port of the zero-photon erasing device is used to input the vacuum state quantum state, and the auxiliary light field output port is connected to the third single-photon detector; the time digital converter receives the optical signals of the first single-photon detector, the second single-photon detector, the third single-photon detector and the fourth single-photon detector and converts them into time information. The signal logic processing unit controls and adjusts the first collimator, the second collimator, the photon signal delay adjustment unit and the optical variable beam splitter according to the time information output by the time digital converter.

[0007] Based on the above, a second electrically-controlled linear translation stage is included, and the signal logic processing unit controls the connection between the first collimator and the second collimator through the second electrically-controlled linear translation stage.

[0008] Based on the above, the first parametric conversion unit and the second parametric conversion unit are nonlinear crystals with a crystal length of 20 mm. The output of the laser is light with a wavelength of 405 nm. The first parametric conversion unit and the second parametric conversion unit convert the light of the first optical path and the light of the second optical path into parametric down-conversion light with wavelengths of 842 nm and 780 nm, respectively.

[0009] Based on the above, the first collimator includes a first concave lens and a first convex lens, the focal length of the first concave lens is f1=-50mm, the focal length of the first convex lens is f2=150mm, the diameters of the first concave lens and the first convex lens are both 25.4mm, and the center points of the first concave lens and the first convex lens are 200mm apart.

[0010] Based on the above, the second collimator includes a second concave lens and a second convex lens, the focal length of the second concave lens is f3=150mm, the focal length of the second convex lens is f4=-50mm, the diameters of the second concave lens and the second convex lens are both 25.4mm, and the center points of the second concave lens and the second convex lens are 200mm apart.

[0011] Based on the above, the polarization unit includes a half-wave plate and a quarter-wave plate, and the light of the second optical path enters the second parameter conversion unit after passing through the half-wave plate and the quarter-wave plate in sequence.

[0012] Based on the above, the photon signal delay adjustment unit includes a first electrically controlled linear translation stage and two prisms, and the first electrically controlled linear translation stage drives and connects the two prisms.

[0013] Based on the above, the zero-photon erasure device is an asymmetric interferometer, which includes a third optical beam splitter, a fourth optical beam splitter, a fourth reflector, a fifth reflector and a third single-photon detector. The light of the second optical path passes through the third optical beam splitter and the fourth optical beam splitter in sequence and then enters the first optical beam splitter; the auxiliary light field input port of the third optical beam splitter is used to input the vacuum state quantum state, and the auxiliary light field passes through the third optical beam splitter and then is reflected by the fourth reflector and the fifth reflector in sequence, and then enters the fourth optical beam splitter. The auxiliary light field output port of the fourth optical beam splitter is connected to the third single-photon detector.

[0014] Based on the above, the transmittance of the third optical beam splitter is T3=0.2, the transmittance of the fourth optical beam splitter is T4=0.24, and the ratio of T3 to T4 is T3:T4=1:1.2; the detection efficiency of the third single-photon detector is η=0.4.

[0015] Compared with the prior art, the present invention has outstanding substantial features and significant progress. Specifically, the present invention adopts a zero-photon erasure scheme to achieve coherence enhancement. The success probability of zero-photon erasure is as high as 90%, the resource consumption caused to quantum states and quantum entangled states is small, the interference visibility of single-photon optical interference is improved, and the photon interference mechanism is adopted to achieve decoupling from noise photons in the background. It has immunity to background noise and greatly improves the effect of non-contact imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the optical principle structure of the present invention.

[0017] Figure 2 It is a schematic block diagram of the logical connection of the optoelectronic device of the present invention.

[0018] Figure 3 Schematic diagram of the optical path structure of the collimator 1 of the present invention.

[0019] Figure 4 Schematic diagram of the optical path structure of the collimator 2 of the present invention.

[0020] Figure 5 It is a schematic diagram of the input and output port structure of the optical beam splitter BS1 of the present invention.

[0021] Figure 6 It is a schematic diagram of the input and output port structure of the optical beam splitter BS2 of the present invention.

[0022] Figure 7 It is a schematic structural diagram of the zero-photon erasing device of the present invention.

[0023] Figure 8 It is a structural schematic diagram of a zero-photon erasing device in the prior art.

[0024] Fig. 9 It is a comparison diagram of the quantum coherence of the quantum state after the zero-photon erase operation using an asymmetric interferometer and the common zero-photon erase operation when the same input is used in the present invention.

[0025] Fig.10 It is a comparison chart of the success probabilities of the zero-photon erase operation using an asymmetric interferometer and a common zero-photon erase operation when the same input is used in the present invention.

[0026] Fig.11 It is a control logic diagram of the optical variable beam splitter of the present invention.

[0027] Fig.12 It is a control logic diagram of the electric-controlled linear translation stage DL1 of the present invention.

[0028] Fig.13 It is a control logic diagram of the electric-controlled linear displacement stage DL2 of the present invention.

[0029] Fig.14 It is a comparison diagram of photon counts on the single-photon detector D1 when the electric-controlled linear displacer DL2 of the present invention moves with a step length of 0.01 mm with and without coherence enhancement. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, a non-contact quantum radar system based on coherence enhancement includes a laser, an optical variable beam splitter, a detection receiving unit and a homogeneity verification unit. The detection receiving unit includes a first parameter conversion unit, a first collimator and a second collimator. The first parameter conversion unit is a nonlinear crystal NL1, and the first collimator is Figure 1 The middle collimator 1, the second collimator is Figure 1 The homogeneity verification unit includes a polarization unit, a second parameter conversion unit, a photon signal delay adjustment unit, a zero photon erasing device, a first optical beam splitter and a second single photon detector, a polarization unit half-wave plate HWP and a quarter-wave plate QWP, a second parameter conversion unit, namely a nonlinear crystal NL2, and a zero photon erasing device, namely Figure 1 In the ZPS, the first optical beam splitter is Figure 1 In the optical beam splitter BS1, the second single photon detector is Figure 1The single photon detector D2. The photon signal delay adjustment unit includes a first electrically controlled linear displacement stage DL1 and two prisms. The two prisms are respectively arranged on the first electrically controlled linear displacement stage DL1. After the light is incident on the first prism, it is reflected back from the second prism. The first electrically controlled linear displacement stage will change the distance traveled by the photon by moving in a straight line, thereby changing the delay of the light.

[0032] The laser uses a continuous output laser, and the output of the laser is a laser with a wavelength of 405nm. The laser is divided into two paths by an optical variable beam splitter, the first optical path reaches the nonlinear crystal NL1, and the other reaches the nonlinear crystal NL2. Both the nonlinear crystal NL1 and the nonlinear crystal NL2 use PPKTP (periodically polarized potassium titanyl phosphate) nonlinear optical crystals, and the crystal length is 20mm. After the parametric down-conversion process on the nonlinear crystal NL1, the first parameter, i.e., the parametric down-conversion light of 842nm and the second parameter, i.e., the parametric down-conversion light of 780nm, will be output. The 842nm light reaches the target through the collimator 1, participates in the interaction with the target, and the signal after being reflected by the target reaches the reflector R1 through the collimator 2, and is reflected by the reflector R1 to reach the reflector R2. The output of the collimator 2 reaches the port 7 of the optical beam splitter BS1 through the reflectors R1 and R2. The parametric down-conversion light of 780nm reaches the port 11 of the optical beam splitter BS2.

[0033] At the same time, the laser of the second optical path of another output port of the optical variable beam splitter is polarized by the half-wave plate HWP and the quarter-wave plate QWP, and the regulated laser reaches the nonlinear crystal NL2, and the fourth parameter, i.e., 780nm light, and the third parameter, i.e., 842nm light, are generated by the parametric down-conversion process on the nonlinear crystal NL2, wherein the photon with a wavelength of 780nm reaches the port 12 of the optical beam splitter BS2. Optical interference occurs on the optical beam splitter BS2, wherein the input ports of the optical beam splitter BS2 are 11 and 12, and the output ports are 13 and 14, and the output ports 13 and 14 of the optical beam splitter BS2 are connected to the fourth single-photon detector D0 and the first single-photon detector D1, respectively.

[0034] The 842nm light on the nonlinear crystal NL2 reaches the 15th port of the zero photon eraser ZPS through the electric stage DL1. The 18th port of the zero photon eraser ZPS is the output port, and the output signal reaches the 8th port of the optical beam splitter BS1 through the reflector R3. The function of the optical beam splitter BS1 is to verify the homogeneity of the photons input from ports 7 and 8, and the verification result is given by the measurement result of the single photon detector D2.

[0035] Preferably, it further comprises a feedback adjustment unit, the feedback adjustment unit comprising a second optical beam splitter, a first single photon detector, a fourth single photon detector, a third single photon detector, a time digital converter and a signal logic processing unit, the second optical beam splitter being Figure 1 The optical beam splitter BS2 in the third single-photon detector is Figure 1 The single photon detector D3. Figure 2 As shown, the single photon detectors D0, D1, D2, and D3 are connected to ports 1, 2, 3, and 4 of the time digital converter (model Time Tagger 20) through radio frequency coaxial cables. The time digital converter converts the radio frequency signal into the photon arrival time, and sends the time information to the signal logic processing unit (actually the software algorithm in the control system) through the USB data line. The signal logic processing unit controls the electric linear stage DL1, the electric linear stage DL2, and the optical variable beam splitter through the RS232 data line. By moving the electric linear stage DL1, the delay between the photon signals can be changed to improve the photon homogeneity. The optical variable beam splitter (model NewPort VA-CB-3-CONEX) is controlled by electrical signals, and the transmittance of the beam splitter can be adjusted. Collimators 1 and 2 are respectively set on the electric linear stage DL2. By moving the electric linear stage DL2, the target can be linearly scanned to achieve target imaging.

[0036] Specifically, Figure 3 The optical path structure diagram of collimator 1 includes a coaxial system composed of two lenses. The input port of collimator 1 is port 3, and the output port is port 4. A is a concave lens with a focal length of f1 = -50mm, and B is a convex lens with a focal length of f2 = 150mm. The diameters of lenses A and B are both 25.4mm, and the center points of the two lenses are 200mm apart.

[0037] Figure 4 The optical path structure diagram of collimator 2 includes a coaxial system composed of two lenses. The input port of collimator 2 is port 5, and the output port is port 6. C is a concave lens with a focal length of f3 = 150 mm, and D is a convex lens with a focal length of f4 = -50 mm. The diameters of both lenses C and D are 25.4 mm, and the center points of the two lenses are 200 mm apart.

[0038] Figure 5 The input and output ports of the optical beam splitter BS1 are set. Port 7 and port 8 are the input ports of the optical beam splitter BS1, and port 9 and port 10 are the output ports of the optical beam splitter BS1. The optical beam splitter BS1 adopts a fixed transmittance optical beam splitter with a transmittance of 0.5.

[0039] Figure 6 The input and output ports of the optical beam splitter BS2 are set. Port 11 and port 12 are the input ports of the optical beam splitter, and port 13 and port 14 are the output ports of the optical beam splitter BS2. The optical beam splitter BS2 adopts a fixed transmittance optical beam splitter with a transmittance of 0.5.

[0040] Figure 7 The structure diagram of the zero-photon erasing device using an asymmetric interferometer in the present invention, the asymmetric interferometer includes a third optical beam splitter BS3, a fourth optical beam splitter BS4, a fourth reflector R4, a fifth reflector R5 and a third single-photon detector D3, the input port of the zero-photon erasing device is port 15, the output port is port 18, and port 16 is an auxiliary light field input port. In the present invention, the input quantum state of the zero-photon erasing auxiliary quantum state, i.e., port 16, is a vacuum state |0>. BS3 and BS4 are both optical beam splitters, the transmittance of BS3 is set to a fixed value T3=0.2, the transmittance of BS4 is set to a fixed value T4=0.24, and the ratio of T3 to T4 is T3:T4=1:1.2. The detection efficiency of the single-photon detector is η=0.4. In theory, the higher the detection efficiency of the single-photon detector, the better the imaging effect. The present invention uses a single-photon detector with a detection efficiency of 40%, which has high technical maturity and its corresponding market supply is sufficient. Figure 7 R4 and R5 are both optical reflectors. The present invention uses a metal reflector with a diameter of 25.4 mm and a reflectivity of 98%.

[0041] As a comparison, Figure 8 A common zero-photon erasure scheme is given in . The zero-photon erasure scheme based on an asymmetric interferometer has a higher probability of success, and the common zero-photon erasure scheme can be compared with the asymmetric interferometer scheme in the present invention. The common zero-photon erasure scheme is implemented by an optical beam splitter BS5 and a single-photon detector D5. Similarly, the single-photon detector D5 still uses a single-photon detector with a detection efficiency of 40%. Figure 8 The input port of the scheme is port 19, and the output port is port 22. In order to compare with the zero-photon erasure scheme based on non-planar symmetric interferometer, the transmittance of BS5 is set to the product of T3 and T4, that is, T5 = 0.048. Fig. 9 The quantum coherence of the quantum state after the zero-photon erase operation using an asymmetric interferometer and the common zero-photon erase operation with the same input is compared. The quantum coherence is measured by the von Neumann entropy of the quantum state: C(ρ) = S(ρ diag )-S(ρ), where ρ is the density matrix of the quantum state in the photon basis, ρ diag is the submatrix composed of the diagonal elements of the density matrix ρ, and S(ρ)=-Tr(ρlnρ) is the von Neumann entropy of ρ. Fig. 9 When the coherent states with the same intensity are input into ports 15 and 19, the quantum coherence of the quantum states output from ports 18 and 22 is compared. It can be seen from Fig. 9 that the zero-photon erasure technology based on an asymmetric interferometer can greatly improve the quantum coherence of the quantum state. The quantum coherence given by the zero-photon erasure in the present invention is about 4.53 times that given by the common zero-photon erasure, which provides a prerequisite for improving the performance of non-contact quantum radar imaging. Fig.10 The success probabilities of the zero-photon erasure operation using an asymmetric interferometer and the common zero-photon erasure operation with the same input are given. Taking the same parameter α as an example, the success probability of the zero-photon erasure scheme based on an asymmetric interferometer is about 1.04 times that of the common zero-photon erasure success probability, which indicates that the proposed scheme has a higher success rate than the common zero-photon erasure scheme. At the same time, it can also be seen that under typical parameters, its success probability is about 90%, which does not cause the consumption of quantum resources while improving the coherence and is feasible.

[0042] The signal logic processing unit is responsible for controlling the optical variable beam splitter, the electronically controlled linear displacement stage DL1, and the electronically controlled linear displacement stage DL2 according to the detection results of the single-photon detectors. In fact, the laser is responsible for continuously outputting laser light, and the spontaneous parametric down-conversion process has the characteristic of random distribution in time. The signal logic processing unit divides the photon results detected within 1 second into 1,000,000 equal time intervals in chronological order, and the duration of each interval is 1 microsecond.

[0043] (1) Fig.11 It is the control logic diagram of the optical variable beam splitter. The signal logic unit realizes the control of the optical variable beam splitter according to the detection results of the single-photon detectors D0 and D1. Specifically, set the counter c0 = 0, c1 = 1, δ = 0.02, i = 0, j = 0. Set i = i + 1, T VOA = 0.01 * i. Gradually increase the transmittance of the optical variable beam splitter in steps of 0.01. For each given transmittance, count the single-photon counts on the single-photon detectors D0 and D1 within 1 second, and calculate the ratio c0 / c1 of the two. Compare whether c0 / c1 satisfies (1 - δ) < c0 / c1 < (1 + δ). If so, it indicates that the optical transmittance of the optical variable beam splitter meets the requirements at this time. If not, continue to increase the T VOA transmittance of the optical variable beam splitter until the corresponding c0 / c1 satisfies the condition.

[0044] (2) Fig.12It is the control logic diagram of the electric control linear displacement stage DL1. By controlling the electric control linear displacer DL1 based on the detection results of the single-photon detectors D0 and D2, the link delay of the 842 nm parametric down-converted light generated by the nonlinear crystal NL2 reaching the port 15 of the zero-photon erasure device ZPS can be effectively increased. The control logic of the electric control linear displacer DL1 still performs feedback control based on the detection results of the single-photon detectors per unit time. The displacement range of the electric control linear displacement stage DL1 is 1 mm - 3000 mm. Taking 1 mm as the step size, the relative displacement in the Y direction is gradually increased until the detection results on the single-photon detectors D0 and D2 are equal. The specific process is as Fig.13 shown. When the system is initialized, the window width is set to 1 microsecond, and δ = 0.02. The cumulative photon count c0 of the single-photon detector D0 = 0, the cumulative photon count c2 of the single-photon detector D2 = 0, and the initial value of the electric control linear displacement stage DL1 is set to DL 1 = 1 mm. If the photon detection result on the single-photon detector D3 at the j-th time window (from the moment j*width to (j + 1)*width, width = 1 us) is 0, then the photon counts of the single-photon detector D0 and the single-photon detector D2 start to be accumulated: c0 = c0 + n0, c2 = c2 + n2.

[0045] Compare the count of the single-photon detector D0 with the count of the single-photon detector D2 within 1 second. If (1 - δ) < c0 / c2 < (1 + δ), it is considered that the delay adjustment of the electric control linear displacer DL1 is successful. Otherwise, continue to increase the displacement of the electric control linear displacement stage DL1 by 1 mm as the step size until the condition (1 - δ) < c0 / c2 < (1 + δ) is met.

[0046] (3) Fig.13 It is the control logic diagram of the electric control linear displacement stage DL2. The control logic of the optical variable beam splitter mainly controls the collimator displacement based on the detection results of the single-photon detectors D1 and D3. The displacement range of the electric control linear displacement stage DL2 is 0.01 mm - 100 mm. The collimator 1 and the collimator 2 are placed on the electric control linear displacement stage DL2. The relative displacement of the electric control linear displacement stage DL2 will drive the collimator 1 and the collimator 2 to move, thereby realizing the scanning of the target.

[0047] The control process is as follows. First, the photon count threshold of each target point is set to Cth=2000, and the photon count c1 on the single photon detector D1 is set to 0. The photon count of each target point is still counted and accumulated at a time interval of 1 microsecond. The photon statistics duration of each target point is 10,000 time intervals, that is, 0.01 seconds. For each time interval, the detection result of the single photon detector D3 is first examined. If D3 detects 0 photons, the photon count of the single photon detector D1 is accumulated: the photon count of the detector D1 is recorded as n1, c1=c1+n1. If the photon count c1 within 0.01 seconds, that is, 10,000 time intervals is less than the preset threshold Cth, it indicates that the optical link is faulty and the optical path needs to be adjusted. If the photon count c1 within 10,000 time intervals is greater than the preset threshold Cth, the detection result of the electric-controlled linear displacer DL2 at the current displacement value is completed, and the electric-controlled linear displacer DL2 is added for the next count.

[0048] Fig.14 Photon counting on the single-photon detector D1 with and without coherence enhancement when the electrically controlled linear displacer D2 of the present invention moves with a step length of 0.01 mm. Fig.14 The figure below shows the spatial distribution of the target's actual reflectivity in the Y direction. The reflectivity is spatially periodically distributed, with a spatial distribution period of 4 mm. Fig.14 The solid line in the figure above shows the imaging effect after coherence enhancement. Fig.14 The dashed line in the figure above shows the imaging effect without coherence enhancement. Fig.14 It can be seen that the imaging scheme using coherence enhancement has a more obvious reflectivity response at key nodes such as Y=2mm, 4mm, 6mm, 8mm, and 10mm, and the imaging accuracy is higher.

[0049] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A non-contact quantum radar system based on coherence enhancement, characterized in that: It includes a laser, an optically variable beam splitter, a detection receiving unit and a homogeneity verification unit. The detection receiving unit includes a first parameter conversion unit, a first collimator and a second collimator. The homogeneity verification unit includes a polarization unit, a second parameter conversion unit, a photon signal delay adjustment unit, a zero photon erasing device, a first optical beam splitter and a second single-photon detector. The light emitted by the laser is divided into a first optical path and a second optical path by the optically variable beam splitter. After the first optical path is converted by the first parameter conversion unit, it passes through the first collimator and reaches the detection target. The reflected light of the detection target reaches the first optical beam splitter after passing through the second collimator. The second optical path passes through the polarization processing of the polarization unit and the conversion processing of the second parameter conversion unit in sequence, and then passes through the photon signal delay adjustment unit and the zero photon erasing device in sequence to reach the first optical beam splitter. The second single-photon detector receives the output of the first optical beam splitter to the first optical path and the second optical path and outputs a verification result.

2. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The invention comprises a feedback adjustment unit, which comprises a second optical beam splitter, a first single-photon detector, a fourth single-photon detector, a third single-photon detector, a time digital converter and a signal logic processing unit. The first parameter of the first optical path converted by the first parameter conversion unit enters the first collimator, and the second parameter enters the second optical beam splitter. The third parameter of the second optical path converted by the second parameter conversion unit enters the photon signal delay adjustment unit, and the fourth parameter enters the second optical beam splitter. The first single-photon detector and the fourth single-photon detector are respectively connected to the output end of the second optical beam splitter; the auxiliary light field input port of the zero-photon erasing device is used to input the vacuum state quantum state, and the auxiliary light field output port is connected to the third single-photon detector; the time digital converter receives the optical signals of the first single-photon detector, the second single-photon detector, the third single-photon detector and the fourth single-photon detector and converts them into time information. The signal logic processing unit controls and adjusts the first collimator, the second collimator, the photon signal delay adjustment unit and the optical variable beam splitter according to the time information output by the time digital converter.

3. The contactless quantum radar system based on coherence enhancement according to claim 2 is characterized in that: It comprises a second electrically controlled linear displacement stage, and the signal logic processing unit controls the connection between the first collimator and the second collimator through the second electrically controlled linear displacement stage.

4. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The first parameter conversion unit and the second parameter conversion unit are nonlinear crystals respectively, and the crystal length is 20mm; the output of the laser is light with a wavelength of 405nm, and the first parameter conversion unit and the second parameter conversion unit convert the light of the first optical path and the light of the second optical path into parametric down-conversion light with wavelengths of 842nm and 780nm respectively.

5. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The first collimator includes a first concave lens and a first convex lens, the focal length of the first concave lens is f1=-50mm, the focal length of the first convex lens is f2=150mm, the diameters of the first concave lens and the first convex lens are both 25.4mm, and the center points of the first concave lens and the first convex lens are 200mm apart.

6. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The second collimator includes a second concave lens and a second convex lens, the focal length of the second concave lens is f3=150mm, the focal length of the second convex lens is f4=-50mm, the diameters of the second concave lens and the second convex lens are both 25.4mm, and the center points of the second concave lens and the second convex lens are 200mm apart.

7. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The polarization unit includes a half-wave plate and a quarter-wave plate, and the light of the second optical path enters the second parameter conversion unit after passing through the half-wave plate and the quarter-wave plate in sequence.

8. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The photon signal delay adjustment unit comprises a first electrically-controlled linear translation stage and two prisms, and the first electrically-controlled linear translation stage drives and connects the two prisms.

9. The contactless quantum radar system based on coherence enhancement according to claim 1, characterized in that: The zero-photon erasing device is an asymmetric interferometer, which includes a third optical beam splitter, a fourth optical beam splitter, a fourth reflector, a fifth reflector and a third single-photon detector, and the light of the second optical path passes through the third optical beam splitter and the fourth optical beam splitter in sequence and then enters the first optical beam splitter; The auxiliary light field input port of the third optical beam splitter is used to input the vacuum state quantum state. After passing through the third optical beam splitter, the auxiliary light field is reflected by the fourth reflector and the fifth reflector in sequence, and then enters the fourth optical beam splitter. The auxiliary light field output port of the fourth optical beam splitter is connected to the third single-photon detector.

10. The contactless quantum radar system based on coherence enhancement according to claim 9, characterized in that: The transmittance of the third optical beam splitter is T3=0.2, the transmittance of the fourth optical beam splitter is T4=0.24, and the ratio of T3 to T4 is T3:T4=1:1.2; the detection efficiency of the third single-photon detector is η=0.4.

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