Quantum radar experimental apparatus based on quantum state comparator

Abstract

The application belongs to the technical field of target detection and identification, and discloses a quantum radar experimental device based on a quantum state comparator, which comprises a transmitter and a receiver, the transmitter comprises a quantum entanglement source, the quantum entanglement source is a three-mode quantum entanglement state prepared by a cascade second-order nonlinear process; the receiver comprises a signal collection unit, two quantum storages, a quantum state comparator and a target information inversion unit, the signal collection unit is used for receiving signals reflected by a target and sending the signals to the two quantum storages respectively, the quantum state comparator is used for comparing quantum states in the two quantum storages, and the target information inversion unit is used for inferring target information according to a comparison result of the quantum state comparator. The application can realize efficient judgment of the existence of a target through the quantum state comparator, and further solve the problem of additional resource consumption caused by quantum measurement in the existing quantum radar.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of target detection and identification, and particularly relates to a quantum radar experimental device based on a quantum state comparator. BACKGROUND

[0002] Quantum radar is a new target detection technology that combines quantum information technology and traditional radar technology, and has strong detection capability for dark weak targets in a strong background. In recent years, quantum information technology has emerged as a new force, and quantum radar technology has become the focus of attention of countries around the world.

[0003] The known quantum radar scheme is to prepare a quantum entangled state and perform quantum state discrimination on the received quantum entangled state to achieve target detection. Quantum state discrimination requires quantum state measurement, which is relatively difficult to design and implement. On the other hand, users are more concerned about the existence of the target binary information reflected by the quantum state information, rather than all the quantum state information provided by the quantum measurement. The redundant quantum state information acquisition process consumes very expensive quantum measurement resources, and greatly limits the actual performance of the quantum radar.

[0004] Therefore, the present application provides a quantum radar device based on a quantum state comparator, which realizes target detection by emitting two quantum signals to the target, collecting two echo signals and sending them into a quantum state comparator. Moreover, the quantum state comparator is completed by an optical beam splitter and a photon detector, without the need for accurate quantum state measurement and discrimination, avoiding the waste of redundant quantum state information, thereby realizing target detection in a strong background. It is a practical quantum radar device that is easy to operate and configure. SUMMARY

[0005] The present application aims to provide a quantum radar experimental device based on a quantum state comparator, and aims to solve the technical problems existing in the prior art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a quantum radar experimental device based on a quantum state comparator, comprising a transmitter and a receiver, the transmitter comprising a quantum entanglement source, the quantum entanglement source being a three-mode quantum entangled state prepared by a cascaded second-order nonlinear process; the receiver comprising a signal collection unit, two quantum storages, a quantum state comparator and a target information inversion unit, the signal collection unit being used for receiving signals reflected by a target and sending the signals to the two quantum storages respectively, the quantum state comparator being used for comparing quantum states in the two quantum storages, and the target information inversion unit being used for inferring target information according to the comparison result of the quantum state comparator.

[0007] In another preferred embodiment of the present invention, the transmitter includes a frequency-stabilized laser and a nonlinear crystal 1 connected thereto, the nonlinear crystal 1 being connected to a nonlinear crystal 2.

[0008] In another preferred embodiment of the present invention, the nonlinear crystal 1 is also connected to an optical mirror 1 and a light collector 1.

[0009] In another preferred embodiment of the present invention, the nonlinear crystal 2 is connected to an optical mirror 3 and a single-photon detector D0, and the optical mirror 3 is connected to a light collector 2.

[0010] In another preferred embodiment of the present invention, an optical reflector 2 is disposed between the nonlinear crystal 1 and the nonlinear crystal 2.

[0011] In another preferred embodiment of the present invention, the quantum state comparator includes three optical beam splitters and four single-photon detectors, the three optical beam splitters being BS1, BS2, and BS3, and the four single-photon detectors being D1, D2, D3, and D4.

[0012] In another preferred embodiment of the present invention, the transmittance of the optical beam splitters is 50%.

[0013] In another preferred embodiment of the present invention, the workflow of the target information inversion unit is as follows: The total number of effective detections M = 1000, N... th =250, photon coincidence count Nc=0, photon emission count m=0; activate single-photon detector D0. If D0 detects a single photon, set m=m+1; then activate single-photon detectors D1, D2, D3, and D4 for single-photon detection. If the target exists, only D1 and D2 have photon coincidence counts, or only D3 and D4 have photon coincidence counts, then set Nc=Nc+1; if the target does not exist, D1 and D2 will not have photon coincidence counts, and D3 and D4 will not have photon coincidence counts, so Nc is not accumulated; compare the magnitude of m with M. If m<M, continue to emit laser light and count photons until m=M, then stop emitting laser light and set the photon coincidence count Nc and Nc+1. th For comparison, if Nc > N th If the objective is clear, it is considered to have a goal; otherwise, it is considered to have no goal.

[0014] The principles and beneficial effects of this invention:

[0015] 1. In this invention, a quantum state comparator is used to output the existence information of the target. The output information is free of redundancy and has a high information utilization rate.

[0016] 2、The application realizes target detection by comparing the two received quantum signals, which have the same source and the same path, and are more robust to environmental noise.

[0017] 3、The application uses a cascade nonlinear process to generate three-mode quantum entanglement, which is the first time to apply three-mode photon number correlation quantum entanglement state to quantum radar.

[0018] 4、The application uses quantum storage to store two echo signals, and has the advantage of adjustable observation range due to the long signal fidelity time of quantum storage.

[0019] 5、The receiver uses two independent quantum storages to store two echo signals, so that the quantum radar failure rate caused by quantum storage fidelity distortion is low.

[0020] 6、The application uses quantum storage to process target echo quantum signals, so that the quantum radar has online and offline processing functions at the same time, and improves the data throughput of the quantum radar and the overload working capacity of the quantum radar under saturation attack.

[0021] In summary, the application proposes a new path for target state differentiation in quantum target detection, realizes a new target detection scheme under the assistance of quantum entanglement state by emitting two quantum signals to the target potential area, realizes efficient judgment of the existence of the target through the quantum state comparator, and can solve the problem of additional resource consumption caused by quantum measurement in the existing quantum radar, which is of great significance for improving the usability, operability and robustness of practical quantum radar.

[0022] Additional aspects and advantages of the application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0023] The above and / or additional aspects and advantages of the application will become apparent and be readily understood from the following description, including the appended drawings, in which:

[0024] Figure 1 is the overall scheme diagram of the embodiment of the application.

[0025] Figure 2 is a structural schematic diagram of the transmitter in the embodiment of the application.

[0026] Figure 3 is a structural schematic diagram of the quantum state comparator in the embodiment of the application.

[0027] Figure 4 is a target information inversion flowchart in the target inversion unit in the embodiment of the application.

[0028] Figure 5 is a photon coincidence counting graph detected in target detection under ideal conditions in the embodiment of the application.

[0029] Figure 6 is a photon coincidence counting graph in the case of target absence and target presence under ideal conditions in target detection in the embodiment of the application.

[0030] Figure 7 is a photon coincidence counting graph of a low reflectivity target under actual conditions in the embodiment of the application.

[0031] Figure 8 is a graph showing the influence of different threshold values on the detection probability in the embodiment of the application. DETAILED DESCRIPTION

[0032] Embodiments of the application are described in detail below with reference to the accompanying drawings, in which the same or similar elements or elements having the same or similar functions are denoted by the same or similar reference numerals throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the application and cannot be understood as a limitation of the application.

[0033] In the description of the application, it should be understood that the terms "longitudinal", "transverse", "vertical", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the application.

[0034] In the description of the application, unless otherwise specified and limited, it should be noted that the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be a mechanical connection or an electrical connection, or a communication between two elements, or a direct connection, or an indirect connection through an intermediate medium, and those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0035] The application provides a quantum radar experimental device based on a quantum state comparator, as shown in Figure 1 The transmitter includes a quantum entanglement source, which is a three-mode quantum entangled state prepared by a cascade second-order nonlinear process. In combination with Figure 2 The transmitter includes a frequency stabilized laser and a nonlinear crystal 1 connected thereto. The frequency stabilized laser is used as a source to excite, and after nonlinear action on the nonlinear crystal 1, a detection signal 1 and a body signal 1 are generated.

[0036] The probe signal 1 is output after collimation by the confocal thin lens L1 and the confocal thin lens L2, and can detect a target at a long distance.

[0037] The nonlinear crystal 1 is connected with the nonlinear crystal 2, and the optical mirror 2 is arranged between the nonlinear crystal 1 and the nonlinear crystal 2. The body signal 1 continues to perform nonlinear action on the nonlinear crystal 2 after passing through the optical mirror 2, to generate the probe signal 2 and the local signal 2. The probe signal 2 is output after collimation by the confocal thin lens L3 and the confocal thin lens L4. The confocal thin lens L1 and the confocal thin lens L3 have the same parameters, and the confocal thin lens L2 and the confocal thin lens L4 have the same parameters.

[0038] The nonlinear crystal 1 is also connected with the optical mirror 1 and the light collector 1. The light collector 1 is used to collect the quantum entangled state reflected by the optical mirror 1, so as to reduce the additional noise introduced by the internal stray light of the transmitter.

[0039] The nonlinear crystal 2 is connected with the single-photon detector D0. The local signal 2 is detected by using the single-photon detector D0, and the detection result can be used as a mark signal.

[0040] The nonlinear crystal 2 is also connected with the optical mirror 3 and the light collector 2. The remaining local signal on the nonlinear crystal 2 reaches the light collector 2 through the optical mirror 3.

[0041] The receiver includes a signal collection unit, two quantum storages, a quantum state comparator, and a target information inversion unit. The two quantum storages are quantum storage 1 and quantum storage 2. The quantum storage 1 and the quantum storage 2 use an adjustable time delay device to delay the optical path, or use a neodymium-doped yttrium vanadate crystal to realize quantum storage. In this embodiment, the adjustable time delay device is used to delay the optical path.

[0042] In combination Figure 3 As shown in the figure, the quantum state comparator includes three optical beam splitters and four single-photon detectors. The three optical beam splitters are BS1, BS2, and BS3, and the transmittance of the three optical beam splitters is 50%. The four single-photon detectors are D1, D2, D3, and D4.

[0043] The use method of the quantum radar experimental device based on the quantum state comparator is as follows:

[0044] Step one, in the transmitter, a frequency stabilization laser is used as a source to excite nonlinear action on the nonlinear crystal 1, to generate the probe signal 1 and the local signal 1. The probe signal 1 is output after collimation by the confocal thin lens L1 and the confocal thin lens L2, to detect a target and output a return signal 1.

[0045] The local signal 1 continues to be nonlinearly affected on the nonlinear crystal 2 after passing through the optical mirror, to generate a probe signal 2 and a local signal 2, the probe signal 2 is output after being collimated by the confocal thin lens L3 and the confocal thin lens L4, to probe the target and output an echo signal 2.

[0046] The local signal 2 is detected by the single photon detector D0, and the detection result is used as a mark signal.

[0047] The remaining local signal on the nonlinear crystal 1 reaches the light collector 1 through the optical mirror 1 for collection, and the remaining local signal on the nonlinear crystal 2 reaches the light collector 2 through the optical mirror 3 for collection, so that the additional noise introduced by the internal stray light of the transmitter can be reduced.

[0048] In step two, in the receiver, the signal collection unit receives the echo signal 1 and the echo signal 2 reflected by the target, and sends the echo signal 1 and the echo signal 2 into the quantum storage 1 and the quantum storage 2 respectively, and then sends the echo signal 1 and the echo signal 2 into the quantum state comparator after being delayed by the adjustable delay unit. The quantum state comparator compares the echo signal 1 and the echo signal 2, and the target information inversion unit infers the target information according to the comparison result of the quantum state comparator. When D1 and D2 both detect one photon or D3 and D4 both detect one photon, it is determined that the target exists, otherwise it is determined that the target does not exist.

[0049] The target information inversion process of the target inversion unit in the receiver is shown in Figure 4 , initially, the total number of effective detections M = 1000, N th = 250, the number of photon coincidences Nc = 0, and the number of photon emissions m = 0. Then the single photon detector D0 is started, if the single photon detector D0 detects a single photon, then m = m + 1, and the single photon detectors D1, D2, D3 and D4 are started to detect single photons.

[0050] According to the quantum state preparation method of the present application, if the target exists, only D1 and D2 have photon coincidence counting, or only D3 and D4 have photon coincidence; if the target does not exist, D1 and D2 do not have photon coincidence counting, and D3 and D4 also do not have photon coincidence.

[0051] If D1 and D2 have photon coincidence counting or D3 and D4 have photon coincidence counting, then Nc = Nc + 1; if D1 and D2 do not have photon coincidence, and D3 and D4 also do not have photon coincidence counting, then Nc does not perform the accumulation operation. Compare m and M, if m < M, continue to let the frequency stabilized laser emit laser and count photons, until m = M, stop emitting laser and compare the number of photon coincidences Nc with N th , if Nc > N thIf yes, it is determined that there is a target, otherwise, it is determined that there is no target.

[0052] According to the technical solution provided by the present application, the following experiments are performed:

[0053] Experiment 1: Photon coincidence count Nc detected under ideal conditions

[0054] From Figure 5 It can be seen that the photon coincidence count Nc increases linearly with the effective detection number M. Assuming that the target reflectivity is κ = 1, the ambient thermal noise level is NB = 0, and the three-mode quantum entanglement is

[0055] When single-photon detection is performed on the local signal 2 and D0 detects a single photon, both the detection signal 1 and the detection signal 2 are single-photon states. Since the target reflectivity κ = 1, the single-photon signals in the detection signal 1 and the detection signal 2 will eventually be received by the receiver and reach the quantum state comparator. Since the transmittance of the optical beam splitter BS1 is 50%, the quantum state evolution of the echo signal 1 and the echo signal 2 after passing through BS1 is Further, the quantum state evolution of |ψ'> after passing through the optical beam splitters BS2 and BS3 is

[0056]

[0057] Wherein |0>1|0>2|0>3|2>4, the subscripts 1-2-3-4 respectively indicate Figure 3 The order number of the light path detected by the detectors D0, D1, D2 and D3.

[0058] According to the quantum state of |ψ">, it is easy to know that the probability of D1 and D2 detecting 1 photon is 1 / 4, and the probability of D3 and D4 detecting 1 photon is 1 / 4.

[0059] Figure 5 In the figure, the D1 and D2 coincidence and the D3 and D4 coincidence results are identified by the dashed line and the box, respectively, and the effective detection number M is the sum of the D1 and D2 coincidence counts and the D3 and D4 coincidence counts.

[0060] Experiment 2: Photon number coincidence in the case where the target does not exist and the target exists in the target detection under ideal conditions

[0061] Taking M = 1000 effective detections, if the target does not exist, the photon number coincidence count is 0; if the target exists, the photon number coincidence count is Nc = 500. Set the intermediate number of the two photon number coincidence counts as the threshold value: N th = 250, therefore, according to the determination rule shown in Figure 5 , the target can be distinguished. In combination with Figure 6As shown, in the ideal case, the detection probability of this quantum radar is 1 and the false alarm probability is 0.

[0062] Experiment three: photon coincidence counting of low reflectivity targets under actual conditions

[0063] The photon coincidence counting distribution of low reflectivity targets under actual conditions is given, wherein the Figure 7 As shown, taking M = 1000 effective detections, the horizontal coordinate is the reflectivity of the target, and the vertical coordinate is the photon coincidence counting, wherein Nc is the sum of the coincidence counts of detectors D1 and D2 and the coincidence counts of D3 and D4.

[0064] Since the reflectivity of the target is κ, the quantum state in echo signal 1 can be written as a quantum mixed state ρ1 = κ|1><1| + (1-κ)|0><0|. The quantum state in echo signal 2 is the same as that in echo signal 1, i.e.

[0065] ρ2 = ρ1. Since there is a vacuum state |0><0| in ρ1 and ρ2, the quantum state after the action of optical beam splitter BS1 on ρ1 and ρ2 is:

[0066] After passing through BS2 and BS3, the reduced matrix composed of the diagonal elements of the quantum states finally reaching detectors D1, D2, D3, and D4 can be expressed as

[0067]

[0068] From we know that contains the term |0011><0011|, and the coefficient is Therefore, the probability of coincidence counting of detectors D3 and D4 is Similarly, the probability of coincidence counting of detectors D3 and D4 is also

[0069] Experiment four: the influence of different threshold values on the detection probability

[0070] Taking M = 1000 effective detections, assuming that the reflectivity of the target κ = 0.2, when the target exists, the coincidence counts of the detectors approximately obey a Gaussian distribution with a mean of and a variance of When the target does not exist, the coincidence counts of the detectors are 0. Therefore, the detection probability can be calculated as P d = 1 - P m = 1 - Prob(N c < N th ).

[0071] According to Figure 7The distribution of photon numbers in the sample is given by setting a threshold value of N. th =λμ m / 2 shows that the detection probability gradually decreases with the parameter λ. Taking λ = 0.8, the detection probability is still greater than 0.99, which satisfies the target detection requirement well.

[0072] In summary, the present invention has the following effects:

[0073] (1) This invention employs a three-mode quantum entangled state The two quantum signals (detection signal 1 and detection signal 2) are used as detection signals. The two signals go through the same optical path and environment, which makes the target information contained in the echo signal greater and the detection performance higher.

[0074] (2) The present invention completes the detection of the target by using a quantum state comparator, without the need to measure the quantum state of the echo signal, making the measurement device simpler and more efficient, and easier to configure and miniaturize.

[0075] (3) The receiver scheme uses quantum memory for storage, which is suitable for the detection, identification and tracking of targets with unknown distances or dynamic targets.

[0076] (4) The threshold in the target information inversion unit of the receiver adopts a dynamic adjustable design. The quantum radar can make dynamic trade-offs in detection probability and resource consumption to suit different application scenarios and application requirements.

[0077] In the description of this specification, references to terms such as "preferred embodiment," "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0078] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A quantum radar experimental device based on a quantum state comparator, comprising a transmitter and a receiver, characterized in that: The transmitter includes a quantum entanglement source, which is a three-mode quantum entangled state prepared by a cascaded second-order nonlinear process; the receiver includes a signal collection unit, two quantum storage units, a quantum state comparator, and a target information inversion unit. The signal collection unit is used to receive the signal reflected back from the target and send the signal to the two quantum storage units respectively. The quantum state comparator is used to compare the quantum states in the two quantum storage units. The target information inversion unit is used to infer the target information based on the comparison result of the quantum state comparator. The transmitter includes a frequency-stabilized laser and a nonlinear crystal 1 connected to it. The nonlinear crystal 1 is connected to a nonlinear crystal 2. The nonlinear crystal 1 is also connected to an optical mirror 1 and a light collector 1. The nonlinear crystal 2 is connected to an optical mirror 3 and a single-photon detector D0. The optical mirror 3 is connected to a light collector 2. An optical mirror 2 is disposed between the nonlinear crystal 1 and the nonlinear crystal 2. The quantum state comparator includes three optical beam splitters and four single-photon detectors. The three optical beam splitters are BS1, BS2, and BS3, and the four single-photon detectors are D1, D2, D3, and D4. The target information inversion unit operates as follows: Set the total effective detection count M=1000, Nth=250, photon coincidence count Nc=0, and photon emission count m=0. Start single-photon detector D0. If D0 detects a single photon, set m=m+1. Then start single-photon detectors D1, D2, D3, and D4 for single-photon detection. If the target exists, only D1 and D2 have photon coincidence counts, or only D3 and D4 have photon coincidence counts, then set Nc=Nc+1. If the target does not exist, D1 and D2 will not have photon coincidences, and D3 and D4 will not have photon coincidence counts, so Nc is not accumulated. Compare m with M. If m < M, continue emitting laser light and counting photons until m = M. Then stop emitting laser light and compare the photon coincidence count Nc with Nth. If Nc > Nth, the target is considered present; otherwise, the target is considered absent.

2. The quantum radar experimental device based on a quantum state comparator according to claim 1, characterized in that: The transmittance of all optical beam splitters is 50%.

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