Four-photon entangled quantum light source and implementation method thereof

Abstract

The invention belongs to the technical field of quantum information science, and particularly relates to a four-photon entangled quantum light source and an implementation method thereof. According to the invention, a multi-hue dry pumping scheme is adopted, so that the three-order nonlinear optical device simultaneously generates two processes of degenerate spontaneous four-wave mixing and non-degenerate spontaneous four-wave mixing under the condition of meeting energy conservation and momentum conservation, thereby enabling associated photon pairs generated by the three-order nonlinear optical device to present entanglement characteristics, and further realizing the generation of a four-photon entanglement state. According to the four-photon entangled quantum light source disclosed by the invention, the improvement of the light quantum entanglement dimension can be realized in a compact, high-stability and extensible form, so that more efficient, safer and more accurate quantum information processing and transmission are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of quantum information science, and particularly relates to a four-photon entangled quantum light source and a method for realizing the same. BACKGROUND

[0002] Quantum entanglement is one of the core resources of quantum information processing and even the realization of quantum Internet, and the parametric down-conversion process in a nonlinear crystal is the most mature way to generate entangled photon pairs. In the above parametric process, the associated photon pairs are generated probabilistically, and by means of modulation and coding of the path, polarization and other degrees of freedom, the preparation of photon entangled states can be achieved. Since the A. Zeilinger group first realized the entanglement exchange between two pairs of entangled photons in 1998, the preparation of multi-photon entangled states has entered the researchers' field of vision. The coherent manipulation of multiple quantum bits and the preparation of entangled states are the basis for developing scalable quantum information technology. The increase in the number of manipulable entangled bits is expected to greatly improve the efficiency of data transmission and quantum information processing, and is also conducive to the realization of more complex quantum logic operations and algorithms.

[0003] In terms of light source preparation, due to the probabilistic generation of photons in the parametric down-conversion process, the brightness of the multi-photon entangled state obtained by extending this method decreases exponentially with the number of entangled photons; and the parametric light platform is mostly based on free space, and the scale of the optical information processing system is large and complex, which is limited in stability and miniaturization. Integrated photonics has become one of the most popular platforms in the preparation of optical quantum states due to its low power consumption, high stability and high scalability. The current development of quantum information technology urgently needs high-performance integrated multi-photon entangled light sources to provide higher-performance entangled resources for quantum information processing systems. SUMMARY

[0004] In view of the above-mentioned demand for multi-photon entangled light sources and the limitations of traditional parametric light platform systems, the present application proposes a method for generating a four-photon entangled quantum light source: a method for modulating an optical frequency comb with a narrow linewidth laser, selecting two coherent sidebands of different wavelengths as pump light input into a third-order nonlinear optical device, under the conditions of satisfying energy conservation and momentum conservation, the degenerate and non-degenerate spontaneous four-wave mixing processes will occur in the third-order nonlinear optical material, and the two processes will associate the generated associated photon pairs with each other, so that a four-photon entangled state can be obtained. Combined with a fiber-compatible device in the communication band to collect and transmit, it has the advantages of integrability, high stability and good scalability.

[0005] The technical solution of the present application is:

[0006] A four-photon entangled quantum light source comprises a multi-color coherent pump light source 1, a first erbium-doped fiber amplifier 2, a second erbium-doped fiber amplifier 3, a first polarization controller 4, a second polarization controller 5, a sideband suppression filter 6, a pump suppression filter 8, an unbalanced interferometer 9, a beam splitter filter 10, a first single-photon detector 11, a second single-photon detector 12, a third single-photon detector 13, a fourth single-photon detector 14, a digital time converter 15, and a third-order nonlinear optical device 7.

[0007] Two output ends of the multi-color pump light source 1 are connected to input ends of the first erbium-doped fiber amplifier 2 and the second erbium-doped fiber amplifier 3 respectively; an output of the first erbium-doped fiber amplifier 2 is connected to one input end of the sideband suppression filter 6 through the first polarization controller 4, and an output of the second erbium-doped fiber amplifier 3 is connected to the other input end of the sideband suppression filter 6 through the second polarization controller 5; the sideband suppression filter 6, the third-order nonlinear optical device 7, the pump suppression filter 8, the unbalanced interferometer 9, and the beam splitter filter 10 are sequentially connected end to end; four output ports of the beam splitter filter 10 are connected to input ends of the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13, and the fourth single-photon detector 14 respectively; output ends of the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13, and the fourth single-photon detector 14 are connected to the digital time converter 15.

[0008] The multi-color coherent pump light source 1 is used to generate multi-color coherent pump light.

[0009] The first erbium-doped fiber amplifier 2 and the second erbium-doped fiber amplifier 3 are used to adjust the optical power of the multi-color coherent pump light.

[0010] The first polarization controller 4 and the second polarization controller 5 are used to adjust the polarization direction of the multi-color coherent pump light, so that the polarization direction of the multi-color coherent pump light is consistent with the polarization direction of the low-loss transmission optical mode designed for the third-order nonlinear optical device.

[0011] The sideband suppression filter 6 is used to suppress sideband noise of the pump light and Raman noise generated in the optical path before the pump light enters the third-order nonlinear optical device.

[0012] The third-order nonlinear optical device 7 is used to generate a four-photon entangled state through a spontaneous four-wave mixing process under multi-color coherent pumping.

[0013] The pump suppression filter 8 is used to suppress residual pump photons output by the third-order nonlinear optical device.

[0014] The non-equilibrium interferometer 9 is used to measure the energy-time entanglement characteristics of the generated four photons;

[0015] The spectral filter 10 is used to distinguish and output the generated corresponding wavelength entangled photon pairs;

[0016] The first single photon detector 11, the second single photon detector 12, the third single photon detector 13, and the fourth single photon detector 14 are used to detect single photon events and convert them into electrical signals;

[0017] The time-to-digital converter 15 is used to record and process the electrical signals output by the first single photon detector 11, the second single photon detector 12, the third single photon detector 13, and the fourth single photon detector 14.

[0018] Further, the multi-color coherent pump light source 1 generates multi-color coherent pump light in the form of an electro-optical frequency comb or a nonlinear Kerr comb.

[0019] Further, the narrow-linewidth laser used by the multi-color coherent pump light source 1 is any one of a solid-state laser, a gas laser, a semiconductor laser, or a dye laser.

[0020] Further, the first polarization controller 4 and the second polarization controller 5 are wave-plate type polarization controllers or fiber loop polarization controllers.

[0021] Further, the third-order nonlinear optical device 7 uses any one of the nonlinear materials that can generate spontaneous four-wave mixing processes, including silicon, silicon dioxide, silicon nitride, and III-V semiconductors.

[0022] Further, the third-order nonlinear optical device 7 is one of a waveguide, an optical crystal, and an optical microcavity in structure.

[0023] Further, the sideband suppression filter 15, the pump suppression filter (17), and the spectral filter (18) are any one of an arrayed waveguide grating, a dense wavelength division multiplexer, and an adjustable bandpass filter.

[0024] Further, the non-equilibrium interferometer 9 is a non-equilibrium Mach-Zehnder interferometer or a non-equilibrium Michelson interferometer.

[0025] Further, the first single photon detector 11, the second single photon detector 12, the third single photon detector 13, and the fourth single photon detector 14 are up-conversion single photon detectors or superconducting nanowire single photon detectors.

[0026] An implementation method of a four-photon entangled quantum light source, the specific process being:

[0027] The multi-color coherent pump light source 1 outputs coherent laser of different wavelengths as pump light from two ports respectively, the first erbium-doped fiber amplifier 2 and the second erbium-doped fiber amplifier 3 adjust the power of the two pump lights of different wavelengths, the two pump lights are adjusted in polarization direction by the first polarization controller 4 and the second polarization controller 5, then the pump light sideband is suppressed by the sideband suppression filter 6, then the two pump lights are input into the third-order nonlinear device 7, under the condition of satisfying the energy conservation and momentum conservation, the degenerate and non-degenerate spontaneous four-wave mixing processes occur in the third-order nonlinear optical device 7 at the same time: the pump photons are annihilated, and the corresponding correlated photon pairs are generated, thereby generating a four-photon state with energy-time entanglement characteristics; the photons output by the third-order nonlinear device 7 are suppressed by the pump suppression filter 8, then the energy-time entanglement characteristics of the four-photon state are measured by inputting into the unbalanced interferometer 9, the output of the unbalanced interferometer 9 is connected to the light splitting filter 10 to select four wavelengths of photons with energy-time entanglement characteristics and input into the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13 and the fourth single-photon detector 14 for detection, and the electrical signals detected are recorded and processed by the digital time converter 15 to obtain the energy-time entanglement characteristics of the four photons.

[0028] The present application has the advantages that: the present application provides a method for generating four-photon entanglement based on third-order nonlinear process, that is, using the spontaneous four-wave mixing process in nonlinear optical material to generate four-photon with entanglement characteristics. All the devices used in the method can be from mature fiber compatible devices in communication band, so that the entanglement source has the characteristics of miniaturization and stable output. At the same time, the number of entangled state photons is expanded, which has important significance for the application of multi-particle quantum entanglement properties and the construction of multi-user quantum network. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a structure schematic diagram of an entangled four-photon quantum light source of the present application;

[0030] Figure 2 It is a multi-color coherent pump source of an entangled four-photon quantum light source of the present application;

[0031] Figure 3 It is a characterization result of an entangled four-photon quantum light source of the present application;

[0032] In the drawings, the components represented by each reference numeral are listed as follows:

[0033] 1. Multicolor coherent pump light source, 2. First erbium-doped fiber amplifier, 3. Second erbium-doped fiber amplifier, 4. First polarization controller, 5. First polarization controller, 6. Sideband suppression filter, 7. Third-order nonlinear optical device, 8. Pump suppression filter, 9. Unbalanced interferometer, 10. Spectral filter, 11. First single-photon detector, 12. Second single-photon detector, 13. Third single-photon detector, 14. Fourth single-photon detector, 15. Digital-to-time converter. DETAILED DESCRIPTION

[0034] The technical principles and solutions of the present invention are described in detail below with reference to the accompanying drawings:

[0035] like Figure 1 As shown, the four-photon entangled quantum light source proposed in the present invention includes a multi-color coherent pump light source 1, a first erbium-doped fiber amplifier 2, a second erbium-doped fiber amplifier 3, a first polarization controller 4, a second polarization controller 5, a sideband suppression filter 6, a pump suppression filter 8, an unbalanced interferometer 9, a spectroscopic filter 10, a first single-photon detector 11, a second single-photon detector 12, a third single-photon detector 13, a fourth single-photon detector 14, a digital-to-time converter 15, and a third-order nonlinear optical device 7;

[0036] The two output ends of the multicolor pump light source 1 are respectively connected to the first erbium-doped fiber amplifier 2 and the second erbium-doped fiber amplifier 3; the first erbium-doped fiber amplifier 2 and the first polarization controller 4 are connected in sequence; the second erbium-doped fiber amplifier 3 and the second polarization controller 5 are connected in sequence; the first polarization controller 4 and the second polarization controller 5 are respectively connected to the two input ends of the sideband suppression filter 6; the sideband suppression filter 6, the third-order nonlinear optical device 7, the pump suppression filter 8, the unbalanced interferometer 9, and the spectroscopic filter 10 are connected in sequence; the four output ports of the spectroscopic filter 10 are respectively connected to the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13, and the fourth single-photon detector 14; the output ports of the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13, and the fourth single-photon detector 14 are respectively connected to the digital-to-time converter 15;

[0037] The polychromatic coherent pump light source 1 is used to generate polychromatic coherent pump light;

[0038] The first erbium-doped fiber amplifier 2 and the second erbium-doped fiber amplifier 3 are used to adjust the optical power of the multi-color coherent pump light;

[0039] The first polarization controller 4 and the second polarization controller 5 are used to adjust the polarization direction of the polychromatic coherent pump light so that the polarization direction of the polychromatic coherent pump light is consistent with the polarization direction of the low-loss transmission optical mode designed for the third-order nonlinear optical device;

[0040] The sideband suppression filter 6 is used to suppress the sideband noise of the pump light and the Raman noise generated in the optical path before the pump light inputting into the third-order nonlinear optical device;

[0041] The third-order nonlinear optical device 7 is used to generate four-photon entangled states by spontaneous four-wave mixing process under polychromatic coherent pump;

[0042] The pump suppression filter 8 is used to suppress the residual pump photons outputted from the third-order nonlinear optical device;

[0043] The unbalanced interferometer 9 is used to measure the energy-time entanglement characteristics of the generated four photons;

[0044] The spectral filter 10 is used to distinguish and output the generated corresponding wavelength entangled photon pairs; the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13 and the fourth single-photon detector 14 are used to detect single-photon events and convert them into electrical signals.

[0045] The time-to-digital converter 15 is used to record and process the electrical signals outputted from the first single-photon detector 11, the second single-photon detector 12, the third single-photon detector 13 and the fourth single-photon detector 14.

[0046] In the embodiment, the polychromatic coherent pump light source 1 is generated by modulating an electro-optic frequency comb with a narrow linewidth laser, which is used to provide a stable seed light for modulating the optical frequency comb. Therefore, the narrow linewidth laser needs to meet the following requirements: capable of wavelength adjustment, and the frequency jitter should be less than the resonance linewidth. In the embodiment, a fiber laser is used, which has a wavelength tuning range of 1540.06-1541.12 nm, a maximum output power of 40 mW, a sideband suppression ratio of 70 dB, and a linewidth of 10 kHz. Figure 2 A polychromatic coherent pump source of an entangled four-photon quantum light source according to an embodiment of the present application, Figure 2 (a) is a modulated electro-optic frequency comb, Figure 2 (b) is to select two comb teeth with a spacing of the free spectral range of the micro-ring device from the modulated optical frequency comb, and the two comb teeth are used as the polychromatic coherent pump source.

[0047] The first erbium-doped fiber amplifier 2 and the second erbium-doped fiber amplifier 3 are used to adjust the pump light power inputted into the third-order nonlinear optical device to ensure the occurrence of degenerate and non-degenerate spontaneous four-wave mixing processes. The erbium-doped fiber amplifier used in the embodiment has a wavelength range of 1525-1565 nm, an input optical power range of -25 dBm-3 dBm, and a saturated output power of 17.2 dBm.

[0048] The first polarization controller 4 and the second polarization controller 5 are used to adjust the polarization direction of the pump light so that the pump light is consistent with the polarization direction of the guided wave mode of the third-order nonlinear optical device 7 after passing through the polarization controller. The FPC561 is used in this embodiment, with a wavelength range of 1260-1625 nm, and an insertion loss of 0.1 dB.

[0049] The sideband suppression filter 6 is used to filter out components other than the required wavelength of the pump light, i.e. the sideband noise of the laser and the Raman noise generated in the fiber system. A cascaded high-suppression dense wavelength division multiplexer with a suppression ratio of >120 dB is used in this embodiment.

[0050] The third-order nonlinear optical device 7 is used to generate spontaneous four-wave mixing processes and generate correlated photons. In this embodiment, a silicon nitride micro-ring device is used. When two pump lights with wavelengths corresponding to the micro-ring resonance wavelength are incident into the silicon nitride micro-ring, under the condition of satisfying the momentum conservation and energy conservation, the degenerate spontaneous four-wave mixing process occurs, i.e. annihilating two pump photons of the same wavelength to generate a correlated photon pair, and the non-degenerate spontaneous four-wave mixing process occurs, i.e. annihilating two pump photons of different wavelengths to generate a correlated photon pair. The above processes occur simultaneously in the silicon nitride micro-ring device, thereby generating a four-photon state with energy-time entanglement properties.

[0051] The pump suppression filter 8 is used to suppress the residual pump light output from the third-order nonlinear device 7. A cascaded high-suppression dense wavelength division multiplexer with a suppression ratio of >50 dB is used in this embodiment.

[0052] The unbalanced interferometer 9 is used to test the energy-time entanglement properties of the generated four photons. In this embodiment, a fiber unbalanced Michelson interferometer is used, with an insertion loss of 3.5 dBm and an arm length difference of 10 ns.

[0053] The spectral filter 10 is used to separate and output entangled photons of different wavelengths through its output end. A cascaded high-suppression dense wavelength division multiplexer 18 with a suppression ratio of >120 dB is used in this embodiment, with a channel spacing of 200 GHz, a 3 dB bandwidth of 0.98 nm, and an insertion loss of 1.5 dB.

[0054] The single-photon detector is used to convert the input single-photon signal into an identifiable electrical signal output, achieving the purpose of single-photon detection and counting. In this embodiment, a superconducting nanowire single-photon detector is used, with a detection efficiency of 75% for 1550 nm band light, a dark count of less than 100 Hz, and a time jitter of 68 ps.

[0055] The time-to-digital converter can accurately measure and record the arrival time of a single photon, convert the time information into a digital signal, and perform digital signal processing and data analysis to achieve photon counting, photon time correlation detection, etc. The present embodiment uses an ID900 time-to-digital converter, and the fast counting rate of each channel is up to 100 Mcps, and the resolution is 100 ps. As shown in Figure 3 Fig. 2 shows the test results of a four-photon entangled quantum light source according to an embodiment of the present application, Figure 3 (a) is a four-photon coincidence counting histogram when the interferometer phase is π; Figure 3 (b) is a four-photon coincidence counting histogram when the interferometer phase is π / 2; Figure 3 (c) is a four-photon interference curve, wherein the four-photon detection rate is 1.07 Hz, and the interference visibility is 95.28±0.03%.

[0056] The present application relates to a four-photon entangled quantum light source, belonging to the field of quantum information science and technology. The present application utilizes two different wavelength pump lasers to pump a third-order nonlinear optical device. Under the condition of satisfying energy conservation and momentum conservation, degenerate and non-degenerate spontaneous four-wave mixing processes will occur simultaneously in the third-order nonlinear optical material. The correlated photon pairs generated by the two processes cannot be distinguished in time, and therefore a four-photon entangled state can be obtained. The four-photon entangled quantum light source disclosed in the present application can realize the improvement of the dimension of optical quantum entanglement in a compact, high-stability and scalable form, thereby realizing more efficient, safer and more accurate quantum information processing and transmission.

Claims

1. A four-photon entangled quantum light source, characterized in that: The invention comprises a multi-color coherent pump light source (1), a first erbium-doped fiber amplifier (2), a second erbium-doped fiber amplifier (3), a first polarization controller (4), a second polarization controller (5), a sideband suppression filter (6), a pump suppression filter (8), an unbalanced interferometer (9), a spectroscopic filter (10), a first single-photon detector (11), a second single-photon detector (12), a third single-photon detector (13), a fourth single-photon detector (14), a digital-to-time converter (15), and a third-order nonlinear optical device (7); The two output ends of the multicolor pump light source (1) are respectively connected to the input end of the first erbium-doped fiber amplifier (2) and the input end of the second erbium-doped fiber amplifier (3); the output of the first erbium-doped fiber amplifier (2) is connected to one input end of the sideband suppression filter (6) after passing through the first polarization controller (4); the output of the second erbium-doped fiber amplifier (3) is connected to the other input end of the sideband suppression filter (6) after passing through the second polarization controller (5); the sideband suppression filter (6), the third-order nonlinear optical device (7), the pump suppression filter (8), the unbalanced interferometer (11), the optical fiber amplifier (12), the optical fiber amplifier (13), the optical fiber amplifier (14), the optical fiber amplifier (15), the optical fiber amplifier (16), the optical fiber amplifier (17), the optical fiber amplifier (18), the optical fiber amplifier (19), the optical fiber amplifier (20), the optical fiber amplifier (21), the optical fiber amplifier (22), the optical fiber amplifier (23), the optical fiber amplifier (24), the optical fiber amplifier (25), the optical fiber amplifier (26), the optical fiber amplifier (27), the optical fiber amplifier (28), the optical fiber amplifier (29), the optical fiber amplifier (3) The instrument (9) and the spectrophotometer (10) are connected end to end in sequence; the four output ports of the spectrophotometer (10) are respectively connected to the input end of the first single-photon detector (11), the input end of the second single-photon detector (12), the input end of the third single-photon detector (13), and the input end of the fourth single-photon detector (14); the output end of the first single-photon detector (11), the output end of the second single-photon detector (12), the output end of the third single-photon detector (13), and the output end of the fourth single-photon detector (14) are connected to the digital-to-time converter (15); The polychromatic coherent pump light source (1) is used to generate polychromatic coherent pump light; The first erbium-doped fiber amplifier (2) and the second erbium-doped fiber amplifier (3) are used to adjust the optical power of multi-color coherent pump light; The first polarization controller (4) and the second polarization controller (5) are used to adjust the polarization direction of the polychromatic coherent pump light so that the polarization direction of the polychromatic coherent pump light is consistent with the polarization direction of the low-loss transmission optical mode designed for the third-order nonlinear optical device; The sideband suppression filter (6) is used to suppress the sideband noise of the pump light and the Raman noise generated in the optical path before the pump light is input into the third-order nonlinear optical device; The third-order nonlinear optical device (7) is used to generate a spontaneous four-wave mixing process under multi-color coherent pumping to generate a four-photon entangled state; The pump suppression filter (8) is used to suppress residual pump photons output by the third-order nonlinear optical device; The unbalanced interferometer (9) is used to measure the energy-time entanglement characteristics of the generated four photons; The optical splitter filter (10) is used to distinguish and output the generated corresponding wavelength entangled photon pairs; The first single-photon detector (11), the second single-photon detector (12), the third single-photon detector (13), and the fourth single-photon detector (14) are used to detect single-photon events and convert them into electrical signals; The time-to-digital converter (15) is used to record and process the electrical signals output by the first single-photon detector (11), the second single-photon detector (12), the third single-photon detector (13), and the fourth single-photon detector (14).

2. A four-photon entangled quantum light source according to claim 1, characterized in that: The polychromatic coherent pump light source (1) generates polychromatic coherent pump light in the form of an electro-optical frequency comb or a nonlinear Kerr frequency comb.

3. The four-photon entangled quantum light source according to claim 1, characterized in that: The narrow linewidth laser used in the multi-color coherent pump light source (1) is any one of a solid laser, a gas laser, a semiconductor laser or a dye laser.

4. The four-photon entangled quantum light source according to claim 1, characterized in that: The first polarization controller (4) and the second polarization controller (5) are wave plate type polarization controllers or optical fiber circular polarization controllers.

5. The four-photon entangled quantum light source according to claim 1, characterized in that: The material used in the third-order nonlinear optical device (7) is any one of all nonlinear materials that can generate a spontaneous four-wave mixing process, and the nonlinear materials that can generate a spontaneous four-wave mixing process include silicon, silicon dioxide, silicon nitride and III-V semiconductors.

6. The four-photon entangled quantum light source according to claim 1, characterized in that: The third-order nonlinear optical device (7) is structurally one of a waveguide, an optical crystal and an optical microcavity.

7. The four-photon entangled quantum light source according to claim 1, characterized in that: The sideband suppression filter (6), the pump suppression filter (8) and the optical splitter filter (10) are any one of an arrayed waveguide grating, a dense wavelength division multiplexer and an adjustable bandpass filter.

8. The four-photon entangled quantum light source according to claim 1, characterized in that: The unbalanced interferometer (9) is an unbalanced Mach-Zehnder interferometer or an unbalanced Michelson interferometer.

9. The four-photon entangled quantum light source according to claim 1, characterized in that: The first single-photon detector (11), the second single-photon detector (12), the third single-photon detector (13), and the fourth single-photon detector (14) are up-conversion single-photon detectors or superconducting nanowire single-photon detectors.

10. A method for realizing a four-photon entangled quantum light source, characterized in that: The four-photon entangled quantum light source according to any one of claims 1 to 10 is used for implementation, and the specific process is as follows: The two ports of the multicolor coherent pump light source (1) respectively output coherent lasers of different wavelengths as pump light. The first erbium-doped fiber amplifier (2) and the second erbium-doped fiber amplifier (3) adjust the power of the two pump lights of different wavelengths. The polarization directions of the two pump lights are adjusted by the first polarization controller (4) and the second polarization controller (5). The pump light sidebands are suppressed by the sideband suppression filter (6). Then, the two pump lights are input into the third-order nonlinear device (7) together. Under the condition of satisfying the energy conservation and momentum conservation conditions, degenerate and non-degenerate spontaneous four-wave mixing processes occur simultaneously in the third-order nonlinear optical device (7): the pump photons are annihilated and corresponding correlated photon pairs are generated, thereby generating A four-photon state with energy-time entanglement characteristics; the photons output by the third-order nonlinear device (7) are suppressed by the pump suppression filter (8) to suppress the residual pump photons, and then input into the unbalanced interferometer (9) to measure the energy-time entanglement characteristics of the four-photon state, the output of the unbalanced interferometer (9) is connected to the spectroscopic filter (10) to select the photons of four wavelengths with energy-time entanglement characteristics and input them into the first single-photon detector (11), the second single-photon detector (12), the third single-photon detector (13), and the fourth single-photon detector (14) for detection, and the detected electrical signals are recorded and processed by the digital-to-time converter (15) to obtain the energy-time entanglement characteristics of the four photons.

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