Chip integrated polarization entangled quantum light source of optical communication wave band and implementation method of chip integrated polarization entangled quantum light source

Abstract

The invention provides a chip integrated polarization entangled quantum light source of an optical communication wave band and an implementation method. The quantum light source comprises an associated two-photon state generation unit and a polarization superposition unit which are integrated on the same chip and are connected in sequence; the polarization superposition unit comprises an optical switch and two polarization rotation-beam combiners; the associated two-photon state generation unit generates an associated two-photon state; the associated two-photon state comprises a polarization state of a first signal photon wave packet, a polarization state of a second signal photon wave packet, a polarization state of a first idle frequency photon wave packet and a polarization state of a second idle frequency photon wave packet; the first polarization rotation-beam combiner rotates the polarization state of the second signal photon wave packet and then carries out cross-polarization superposition on the polarization state of the second signal photon wave packet and the polarization state of the first signal photon wave packet; the optical switch determines a selected polarization state based on a self working state; and the second polarization rotation-beam combiner rotates the selected polarization state and then performs cross-polarization superposition on the selected polarization state and the unselected polarization state. According to the invention, the generation of four polarization entangled states is realized through on-chip photoelectric regulation and control.

Description

Technical Field

[0001] The present invention relates to the field of quantum information science and technology, and in particular to a chip-integrated polarization entangled quantum light source in an optical communication band and an implementation method thereof. Background Art

[0002] Quantum entanglement is one of the key resources in the field of quantum information and the basis of many quantum information applications, including quantum teleportation, quantum key distribution, quantum computing, etc. Therefore, the quantum light source that realizes the generation of entangled light quantum states is a very important unit device in the optical quantum information system. At present, there are two main methods to develop entangled quantum light sources.

[0003] The first is through spontaneous parametric down-conversion (SPDC) in a second-order nonlinear crystal. In this process, a pump photon is annihilated and a pair of signal / idler photons are generated. When a specific phase matching technique is met, the collected signal / idler photons have the characteristics of quantum correlation. In recent years, people have used periodically polarized lithium niobate (PPLN) technology to generate entangled two-photon pairs in the communication band. This polarization entanglement implementation method only has nonlinear media on the chip, and requires many discrete optical devices to form a complex optical path outside the chip. And the manipulation of polarization entangled states cannot be achieved through on-chip optoelectronic regulation.

[0004] The second method is to rely on spontaneous four-wave mixing (SFWM) to generate correlated two-photon states in the communication band. In this process, two pump photons are annihilated to generate a pair of signal / idler photons with quantum correlation characteristics. Through appropriate optical path design, the generation of multiple quantum entangled states can be achieved. This type of quantum light source can be realized through common third-order nonlinear waveguide media such as quartz optical fiber and silicon waveguide, and the entangled photon pairs generated are in the optical communication band, which is very suitable for combination with optical fiber communication networks. However, these schemes can only generate specific types of polarization-entangled two-photon states, and cannot achieve the output of arbitrary polarization-entangled two-photon states through on-chip optoelectronic regulation.

[0005] Considering that polarization is an important property of photons, polarization-entangled two-photon states are widely used in related research on quantum communication and quantum information processing. The high-quality realization of the generation of polarization-entangled quantum states has become an important issue in the development of chip-integrated entangled quantum light source devices. Summary of the invention

[0006] The present invention provides a chip-integrated polarization entangled quantum light source in the optical communication band and an implementation method thereof, which is used to solve the defect that the output of arbitrary polarization entangled two-photon states cannot be achieved through on-chip photoelectric regulation in the prior art. The present invention achieves the generation of four polarization entangled states through on-chip photoelectric regulation.

[0007] The present invention provides a chip-integrated polarization entangled quantum light source in an optical communication band, comprising a correlated two-photon state generating unit and a polarization superposition unit which are integrated on the same chip and connected in sequence; the correlated two-photon state generating unit is used to generate correlated two-photon states; the correlated two-photon states include the polarization state of a first signal photon wave packet, the polarization state of a second signal photon wave packet, the polarization state of a first idler photon wave packet and the polarization state of a second idler photon wave packet; the polarization superposition unit comprises an optical switch and two polarization rotation-combiners; the input end of the first polarization rotation-combiner serves as the first input end of the polarization superposition unit, one end of the optical switch serves as the second input end of the polarization superposition unit, and the other end of the optical switch is connected to the input end of the second polarization rotation-combiner; the output end of the first polarization rotation-combiner serves as the output end of the The first output end of the polarization superposition unit, and the output end of the second polarization rotation-combiner serve as the second output end of the polarization superposition unit; the first polarization rotation-combiner is used to rotate the polarization state of the second signal photon wave packet and perform orthogonal polarization superposition with the polarization state of the first signal photon wave packet; the optical switch is used to determine the selected polarization state based on its own working state; the selected polarization state is the polarization state selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; the second polarization rotation-combiner is used to rotate the selected polarization state and perform orthogonal polarization superposition with the unselected polarization state; finally four polarization entangled states are generated; the unselected polarization state is the polarization state that is not selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet.

[0008] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the correlated two-photon state generating unit comprises a pump beam splitter, two nonlinear optical waveguides, a waveguide phase shifter and two spectroscopic filters; the first output end of the pump beam splitter is connected to the input end of the first nonlinear optical waveguide, the second output end of the pump beam splitter is connected to the input end of the second nonlinear optical waveguide, the output end of the first nonlinear optical waveguide is connected to the input end of the first spectroscopic filter, the output end of the second nonlinear optical waveguide is connected to the input end of the waveguide phase shifter, the output end of the waveguide phase shifter is connected to the input end of the second spectroscopic filter, the first output end of the first spectroscopic filter is connected to the first input end of the first polarization rotator-combiner, and the second output end of the first spectroscopic filter is connected to the optical switch. The first input end of the optical switch is connected to the first output end of the second optical splitter filter, and the second output end of the second optical splitter filter is connected to the second input end of the first polarization rotator-combiner; the pump beam splitter is used to split the pump laser so that the split light enters the first nonlinear optical waveguide and the second nonlinear optical waveguide respectively to stimulate spontaneous nonlinear optical processes and generate optical communication band associated two-photon pairs; the waveguide phase shifter is used to change the phase of the optical communication band associated two-photon pairs generated by the second nonlinear optical waveguide; the first optical splitter filter is used to output the polarization state of the first signal photon wave packet and the polarization state of the first idler photon wave packet; the second optical splitter filter is used to output the polarization state of the second signal photon wave packet and the polarization state of the second idler photon wave packet.

[0009] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the chip is a silicon photonic integrated chip or a thin-film lithium niobate chip.

[0010] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the optical switch is an MZI-type optical switch or a MEMS-type optical switch based on an adiabatic coupling structure.

[0011] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the polarization rotation-combiner is a polarization rotation-combiner based on an asymmetric directional coupling structure or a polarization rotation-combiner based on an orthogonal polarization coupling structure.

[0012] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the nonlinear optical waveguide is a waveguide supporting spontaneous four-wave mixing or a waveguide supporting spontaneous parametric down-conversion; the waveguide supporting spontaneous four-wave mixing includes a silicon waveguide, a silicon nitride waveguide, a silicon dioxide waveguide and an arsenic sulfide waveguide, and the waveguide supporting spontaneous parametric down-conversion includes a periodically poled lithium niobate waveguide, a periodically poled thin-film lithium niobate waveguide and a periodically poled thin-film lithium tantalate waveguide.

[0013] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the waveguide phase shifter is a thermo-optical phase shifter or an electro-optical phase shifter.

[0014] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, the spectroscopic filter is a bandpass filter based on a waveguide coupling structure, a bandpass filter based on a microring resonator, or a bandpass filter based on AMZI.

[0015] According to a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention, when the optical switch is in a through state, the selected polarization state is the polarization state of the second idler photon wave packet; when the optical switch is in a cross state, the selected polarization state is the polarization state of the first idler photon wave packet.

[0016] The present invention also provides a method for realizing a chip-integrated polarization entangled quantum light source in an optical communication band, which is realized by using the above-mentioned chip-integrated polarization entangled quantum light source in an optical communication band. The specific process is: generating a correlated two-photon state by a correlated two-photon state generating unit; the correlated two-photon state includes a polarization state of a first signal photon wave packet, a polarization state of a second signal photon wave packet, a polarization state of a first idler photon wave packet, and a polarization state of a second idler photon wave packet; rotating the polarization state of the second signal photon wave packet by a first polarization rotation-combiner and combining it with the first signal The polarization states of the first idler photon wave packets are orthogonally superimposed on each other; the selected polarization state is determined by an optical switch based on its own working state; the selected polarization state is a polarization state selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; the selected polarization state is rotated by a second polarization rotation-combiner and then orthogonally superimposed with an unselected polarization state; and finally four polarization entangled states are generated; the unselected polarization state is a polarization state that is not selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet.

[0017] The present invention provides a chip-integrated polarization entangled quantum light source in an optical communication band and an implementation method, wherein the quantum light source includes an associated two-photon state generating unit and a polarization superposition unit which are integrated on the same chip and connected in sequence; the polarization superposition unit includes an optical switch and two polarization rotation-combiners; the associated two-photon state generating unit generates an associated two-photon state; the associated two-photon state includes the polarization state of the first signal photon wave packet, the polarization state of the second signal photon wave packet, the polarization state of the first idler frequency photon wave packet and the polarization state of the second idler frequency photon wave packet; the first polarization rotation-combiner rotates the polarization state of the second signal photon wave packet and performs orthogonal polarization superposition with the polarization state of the first signal photon wave packet; the optical switch determines the selected polarization state based on its own working state; the second polarization rotation-combiner rotates the selected polarization state and performs orthogonal polarization superposition with the unselected polarization state. The present invention realizes the generation of four polarization entangled states through on-chip photoelectric regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is one of the structural schematic diagrams of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0020] Figure 2 This is the second structural schematic diagram of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0021] Figure 3 This is the third structural schematic diagram of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0022] Figure 4 This is the fourth structural schematic diagram of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0023] Figure 5 It is a flow chart of a method for realizing a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention.

[0024] Reference numerals: 1: correlated two-photon state generation unit; 2: polarization superposition unit; 3: chip; 11: pump beam splitter; 121: first nonlinear optical waveguide; 122: second nonlinear optical waveguide; 13: waveguide phase shifter; 141: first spectroscopic filter; 142: second spectroscopic filter; 21: optical switch; 221: first polarization rotation-beam combiner; 222: second polarization rotation-beam combiner; 31: silicon photonic integrated chip; 32: thin-film lithium niobate chip; 211: Mach-Zehnder interferometer; 212: thin-film lithium niobate optical switch; 131: thermo-optic phase shifter; 132: electro-optic phase shifter. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are 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.

[0026] Please refer to Figure 1 , Figure 1 This is one of the structural schematic diagrams of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0027] The present invention provides a chip-integrated polarization entangled quantum light source in an optical communication band, comprising a correlated two-photon state generating unit 1 and a polarization superposition unit 2 which are integrated on the same chip 3 and connected in sequence; the correlated two-photon state generating unit 1 is used to generate correlated two-photon states; the correlated two-photon states include the polarization state of a first signal photon wave packet, the polarization state of a second signal photon wave packet, the polarization state of a first idler frequency photon wave packet and the polarization state of a second idler frequency photon wave packet; the polarization superposition unit 2 includes an optical switch 21 and two polarization rotation-beam combiners; the input end of the first polarization rotation-beam combiner 221 serves as the first input end of the polarization superposition unit 2, one end of the optical switch 21 serves as the second input end of the polarization superposition unit 2, and the other end of the optical switch 21 is connected to the input end of the second polarization rotation-beam combiner 222; The output end of the device 221 serves as the first output end of the polarization superposition unit 2, and the output end of the second polarization rotation-combiner 222 serves as the second output end of the polarization superposition unit 2; the first polarization rotation-combiner 221 is used to rotate the polarization state of the second signal photon wave packet and perform orthogonal polarization superposition with the polarization state of the first signal photon wave packet; the optical switch 21 is used to determine the selected polarization state based on its own working state; the selected polarization state is the polarization state selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; the second polarization rotation-combiner 222 is used to rotate the selected polarization state and perform orthogonal polarization superposition with the unselected polarization state; and finally four polarization entangled states are generated; the unselected polarization state is the polarization state that is not selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet.

[0028] Please refer to Figure 2 , Figure 2 The second structural schematic diagram of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0029] As a preferred embodiment, the associated two-photon state generating unit 1 includes a pump beam splitter 11, two nonlinear optical waveguides, a waveguide phase shifter 13 and two spectroscopic filters; the first output end of the pump beam splitter 11 is connected to the input end of the first nonlinear optical waveguide 121, the second output end of the pump beam splitter 11 is connected to the input end of the second nonlinear optical waveguide 122, the output end of the first nonlinear optical waveguide 121 is connected to the input end of the first spectroscopic filter 141, the output end of the second nonlinear optical waveguide 122 is connected to the input end of the waveguide phase shifter 13, the output end of the waveguide phase shifter 13 is connected to the input end of the second spectroscopic filter 142, the first output end of the first spectroscopic filter 141 is connected to the first input end of the first polarization rotation-combiner 221, and the second output end of the first spectroscopic filter 141 is connected to the optical switch 21 The first input end of the optical switch 21 is connected to the first output end of the second optical splitter filter 142, and the second output end of the second optical splitter filter 142 is connected to the second input end of the first polarization rotation-combiner 221; the pump beam splitter 11 is used to split the pump laser so that the split light enters the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122 respectively to stimulate spontaneous nonlinear optical processes and generate optical communication band associated two-photon pairs; the waveguide phase shifter 13 is used to change the phase of the optical communication band associated two-photon pairs generated by the second nonlinear optical waveguide 122; the first optical splitter filter 141 is used to output the polarization state of the first signal photon wave packet and the polarization state of the first idler photon wave packet; the second optical splitter filter 142 is used to output the polarization state of the second signal photon wave packet and the polarization state of the second idler photon wave packet.

[0030] In order to realize a chip-integrated quantum light source that can generate all four polarization entangled Bell states, the present invention provides a chip-integrated polarization entangled quantum light source in the optical communication band, which includes a correlated two-photon state generating unit 1 and a polarization superposition unit 2, and the two parts are integrated on the same chip 3 and directly connected.

[0031] The correlated two-photon state generating unit 1 may include a pump beam splitter 11, two nonlinear optical waveguides (a first nonlinear optical waveguide 121 and a second nonlinear optical waveguide 122), a waveguide phase shifter 13 and two spectroscopic filters (a first spectroscopic filter 141 and a second spectroscopic filter 142). After the pump laser of a specific polarization is coupled into the chip 3, it is first evenly divided into two beams by the pump beam splitter 11, and enters the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122 respectively to stimulate spontaneous nonlinear optical processes, including spontaneous four-wave mixing processes or spontaneous parametric down-conversion processes, to generate photon pairs in a specific polarization optical communication band. The two photons contained in the photon pair have different frequencies, the low frequency is called a signal photon, and the high frequency is called an idler photon, which are abbreviated as s and i respectively. The waveguide phase shifter 13 is connected to the second nonlinear optical waveguide 122, and is used to change the phases of the signal photons and idler photons generated in the second nonlinear optical waveguide 122. The wave packets of the signal photons and idler photons of a specific frequency generated in each waveguide are respectively selected by the spectroscopic filter connected to the waveguide to be output at two filter output ports in a specific polarization state and enter the polarization superposition unit 2. Without loss of generality, the specific polarization state of the output wave packets of each port can be defined as horizontal polarization, abbreviated as H. Therefore, the polarization state of the signal photons and idler photons generated in the first nonlinear optical waveguide 121 can be recorded as and , and its corresponding correlated two-photon state can be recorded as The polarization states of the signal photons and idler photons generated in the second nonlinear optical waveguide 122 can be expressed as and , and its corresponding correlated two-photon state can be recorded as .

[0032] The polarization superposition unit 2 may include two polarization rotation-beam combiners (a first polarization rotation-beam combiner 221 and a second polarization rotation-beam combiner 222) and a 2×2 optical switch 21. The polarization state of the first signal photon packet output from the first spectroscopic filter 141 of the associated two-photon state generating unit 1 is input to the first input end of the first polarization rotation-beam combiner 221 as H polarization. The polarization state of the second signal photon packet output from the second spectroscopic filter 142 of the associated two-photon state generating unit 1 is input to the second input end of the first polarization rotation-beam combiner 221 as H polarization. The first polarization rotation-beam combiner 221 rotates the polarization state of the second signal photon packet by 90 degrees to a vertical polarization, abbreviated as V, and then performs orthogonal polarization superposition with the polarization state of the first signal photon packet and outputs it from the output port of the first polarization rotation-beam combiner 221. As a result, the polarization states of the signal photons output at the output end of the first polarization rotation-beam combiner 221 are respectively and . The polarization state of the first idler photon wave packet output from the first spectroscopic filter 141 of the associated two-photon state generating unit 1 is input to the first input end of the 2×2 optical switch 21 as H polarization. The polarization state of the second idler photon wave packet output from the second spectroscopic filter 142 of the associated two-photon state generating unit 1 is input to the second input end of the 2×2 optical switch 21 as H polarization. The two output ports of the 2×2 optical switch 21 are respectively connected to the two input ports of the second polarization rotation-combiner 222 (the other end of the optical switch 21 is connected to the input end of the second polarization rotation-combiner 222).

[0033] If the 2×2 optical switch 21 works in the through state, the polarization state of the second idler photon packet will rotate 90 degrees in the second polarization rotation-combiner 222 to become V polarization, and will be orthogonally polarized with the polarization state of the first idler photon packet and then output from the output port of the second polarization rotation-combiner 222. Therefore, the polarization states of the idler photons output at the output end of the second polarization rotation-combiner 222 are respectively and At this time, the polarization entangled state output by the chip is a two-way correlated two-photon state. and The polarization superposition of , where the phase It can be controlled by the waveguide phase shifter 13. Controlled to 0 and , can be output as polarization entangled state.

[0034] If the 2×2 optical switch 21 works in the cross state, the polarization state of the first idler photon packet will rotate 90 degrees in the second polarization rotation-combiner 222 to become V polarization, and will be orthogonally polarized with the polarization state of the second idler photon packet and then output from the output port of the second polarization rotation-combiner 222. Therefore, the polarization states of the idler photons output at the output end of the second polarization rotation-combiner 222 are respectively and At this time, the polarization entangled state output by the chip is a two-way correlated two-photon state. and The polarization superposition of , where the phase It can be controlled by the waveguide phase shifter 13. Controlled to 0 and , can be output as Therefore, the optical path can realize the generation of all four polarization entangled Bell states.

[0035] In the above introduction, the low-frequency photon in the two photons contained in the photon pair is called the signal photon, and the high-frequency photon is called the idler photon, which are abbreviated as s and i respectively. The above description still holds true if the high-frequency photon in the two photons contained in the photon pair is called the signal photon and the low-frequency photon is called the idler photon.

[0036] The present invention can support the generation of all four polarization entangled Bell states by regulating the waveguide phase shifter 13 on the chip 3 and changing the working state of the 2×2 optical switch 21. In the present invention, all unit devices are integrated on the same chip 3, and no polarization control device outside the chip 3 is required to achieve switching between polarization entangled Bell states. The present invention can be used for both the third-order nonlinear waveguide chip 3 supporting spontaneous four-wave mixing quantum light source and the second-order nonlinear waveguide chip 3 supporting spontaneous parametric down-conversion.

[0037] As a preferred embodiment, the chip 3 is a silicon photonic integrated chip 31 or a thin-film lithium niobate chip 32 .

[0038] In this embodiment, a silicon photonic integrated chip 31 may be used as a basic platform. Silicon material has excellent optical properties, high refractive index contrast, and mature micro-nano processing technology, and can realize highly integrated and high-performance optical devices.

[0039] Of course, a thin-film lithium niobate chip 32 may also be used as a basic platform. Lithium niobate has excellent electro-optical effect and nonlinear optical properties, and can achieve efficient optical modulation and generation of photon pairs.

[0040] As a preferred embodiment, the optical switch 21 is an MZI-based optical switch or a MEMS-based optical switch with an adiabatic coupling structure.

[0041] In this embodiment, the optical switch 21 may be an optical switch based on a Mach-Zehnder Interferometer (MZI) type or a MEMS (Micro-Electro-Mechanical Systems) type optical switch based on an adiabatic coupling structure.

[0042] For example, the optical switch 21 can use a Mach-Zehnder interferometer 211. The Mach-Zehnder interferometer 211 is composed of two beam splitters and two reflectors to form an interference loop. The input light is split into two beams by the first beam splitter, passes through two arms respectively, and then recombines at the second beam splitter. By introducing a phase difference in one of the arms, the interference result of the two beams can be changed, thereby controlling the path and intensity of the output light.

[0043] Of course, the optical switch 21 may also be a thin-film lithium niobate optical switch 212. The thin-film lithium niobate optical switch 212 has an excellent electro-optical effect. Applying an electric field E to the thin-film lithium niobate can change its refractive index n, thereby changing the propagation path and phase of light.

[0044] As a preferred embodiment, the polarization rotation-beam combiner is a polarization rotation-beam combiner based on an asymmetric directional coupling structure or a polarization rotation-beam combiner based on an orthogonal polarization coupling structure.

[0045] In this embodiment, the polarization rotation-combiner can adopt a polarization rotation-combiner with an asymmetric directional coupler structure. The polarization rotation-combiner with an asymmetric directional coupler structure is composed of two waveguides, wherein the width of one waveguide is greater than the width of the other waveguide, forming an asymmetric structure. When light enters a narrow waveguide from a wide waveguide, the polarization state of the light rotates due to the change in the mode field distribution.

[0046] The polarization rotator-beam combiner may adopt a polarization rotator-beam combiner based on an orthogonal polarization coupling structure, which has high efficiency, high integration and wide band characteristics.

[0047] Of course, the polarization rotator-combiner can also adopt a polarization rotator-combiner with a multi-layer curved waveguide structure. The polarization rotator-combiner with a multi-layer curved waveguide structure is composed of multiple layers of curved waveguides, and the bending radius and interlayer spacing of each layer of waveguide are precisely designed to achieve polarization state rotation and beam combining of light. When light propagates in a curved waveguide, the polarization state of the light rotates due to the change in the mode field distribution.

[0048] As a preferred embodiment, the nonlinear optical waveguide is a waveguide supporting spontaneous four-wave mixing or a waveguide supporting spontaneous parametric down-conversion; the waveguide supporting spontaneous four-wave mixing includes silicon waveguide, silicon nitride waveguide, silicon dioxide waveguide and arsenic sulfide waveguide, and the waveguide supporting spontaneous parametric down-conversion includes periodically poled lithium niobate waveguide, periodically poled thin film lithium niobate waveguide and periodically poled thin film lithium tantalate waveguide.

[0049] In this embodiment, the silicon waveguide, as a nonlinear optical waveguide supporting spontaneous four-wave mixing (SFWM), has a high nonlinear coefficient and a high refractive index contrast, which can effectively enhance the interaction between light and light, thereby improving the generation efficiency of correlated two-photon states.

[0050] Periodically poled lithium niobate waveguides are used as nonlinear optical waveguides to support spontaneous parametric down-conversion (SPDC). The periodically poled structure can effectively enhance the nonlinear effect of the waveguide and improve the generation efficiency and coherence of photon pairs.

[0051] As a preferred embodiment, the waveguide phase shifter 13 is a thermo-optical phase shifter 131 or an electro-optical phase shifter 132 .

[0052] As a preferred embodiment, the spectroscopic filter is a bandpass filter based on a waveguide coupling structure, a bandpass filter based on a microring resonator, or a bandpass filter based on AMZI.

[0053] As a preferred embodiment, when the optical switch 21 is in the through state, the polarization state selected is the polarization state of the second idler photon packet; when the optical switch 21 is in the cross state, the polarization state selected is the polarization state of the first idler photon packet.

[0054] Please refer to Figure 3 , Figure 3 The third structural schematic diagram of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0055] In this embodiment, the spectroscopic filter may be a bandpass filter based on a waveguide coupling structure, a bandpass filter based on a microring resonator, or a bandpass filter based on an AMZI (Asymmetric Mach-Zehnder Interferometer).

[0056] The quantum light source adopts a silicon-on-insulator (SOI) substrate and is prepared by a conventional silicon photonic integrated chip process. It is divided into a correlated two-photon state generation unit 1 and a polarization superposition unit 2. In the correlated two-photon state generation unit 1, the pump beam splitter 11 adopts a 1×2 multimode interferometer. The nonlinear optical waveguide (the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122) adopts a single-mode silicon waveguide, and the correlated two-photon pairs are generated by spontaneous four-wave mixing (SFWM) in the silicon waveguide. The waveguide phase shifter 13 is a thermo-optical phase shifter 131 connected to the silicon waveguide to achieve phase control of the correlated two-photon pairs generated in the second nonlinear optical waveguide 122. The spectroscopic filter (the first spectroscopic filter 141 and the second spectroscopic filter 142) adopts a cascaded narrow-band bandpass filter with a grating-assisted directional coupler structure. In the polarization superposition unit 2, the 2×2 optical switch 21 adopts a 2×2 Mach-Zehnder interferometer 211, and the polarization rotation-combiner (the first polarization rotation-combiner 221 and the second polarization rotation-combiner 222) adopts a wide-narrow combined asymmetric directional coupler structure.

[0057] In practical applications, after the 1.5m optical communication band pump laser is coupled into the chip 3 through a quartz fiber, it is first split into two beams with equal success rates by a 1×2 multimode interferometer, and then respectively input into a single-mode silicon waveguide to stimulate a spontaneous four-wave mixing process to generate correlated two-photon pairs. The phase of the correlated two-photon pairs generated by the second nonlinear optical waveguide 122 (single-mode silicon waveguide) can be controlled by a thermo-optical phase shifter 131. Thus, the correlated two-photon states generated in the single-mode silicon waveguide are and . Subsequently, the correlated two-photon pair is input into a cascaded narrowband bandpass filter using a grating-assisted directional coupler structure to extract the signal / idler photons of the corresponding band. Then, the two signal photons are input into a polarization rotator-combiner using an asymmetric directional coupler structure and output, and the polarization states of the output signal photons are and The two idle photons first pass through a 2×2 Mach-Zehnder interferometer 211, and then are input into the polarization rotation-combiner using an asymmetric directional coupler structure and output. When the 2×2 Mach-Zehnder interferometer 211 works in the through state, the polarization states of the idle photons output from the output end of the polarization rotation-combiner 222 are respectively and At this time, the polarization entangled state output by the chip is a two-way correlated two-photon state. and The polarization superposition of , where the phase It can be controlled by the thermo-optical phase shifter 131. Controlled to 0 and , can be output as polarization entangled state; when the 2×2 Mach-Zehnder interferometer 211 works in the cross state, the polarization states of the idler photons output from the output end of the polarization rotation-combiner are and At this time, the polarization entangled state output by the chip is a two-way correlated two-photon state. and The polarization superposition of , where the phase It can be controlled by the thermo-optical phase shifter 131. Controlled to 0 and , can be output as As a result, the chip can output four different polarization entangled states.

[0058] Please refer to Figure 4 , Figure 4 The fourth structural schematic diagram of a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0059] In this embodiment, the quantum light source adopts a thin film lithium niobate substrate and is prepared by a thin film lithium niobate chip 32 process, and is divided into a correlated two-photon state generation unit 1 and a polarization superposition unit 2. In the correlated two-photon state generation unit 1, the pump beam splitter 11 adopts a 1×2 multimode interferometer. The nonlinear optical waveguide adopts a periodically polarized single-mode thin film lithium niobate waveguide, which are respectively called the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122, and the correlated two-photon pairs are generated by spontaneous parametric down conversion (SPDC) in the periodically polarized single-mode thin film lithium niobate waveguide. The waveguide phase shifter 13 is an electro-optical phase shifter 132 connected to the waveguide to achieve phase control of the correlated two-photon pairs generated in the second waveguide. The spectroscopic filter adopts a narrowband bandpass filter with a microring resonator structure. In the polarization superposition unit 2, the 2×2 optical switch 21 adopts a 2×2 thin film lithium niobate optical switch 212. The polarization rotation-combiner adopts a polarization rotation-combiner with a multi-layer curved waveguide structure.

[0060] In practical applications, after the pump laser is coupled into the chip 3 through the quartz fiber, it is first split into two beams with equal success rates by a 1×2 multimode interferometer, and then respectively input into the periodically polarized single-mode thin-film lithium niobate waveguide to stimulate spontaneous parametric down-conversion to generate correlated two-photon pairs. The phase of the correlated two-photon pairs generated by the second nonlinear optical waveguide 122 can be regulated by the electro-optical phase shifter 132. Thus, the correlated two-photon states generated in the periodically polarized single-mode thin-film lithium niobate waveguide are respectively and Subsequently, the correlated two-photon pair is input into a narrowband bandpass filter using a microring resonator structure to extract the signal / idler photons of the corresponding band. Then, the two signal photons are input into a polarization rotator-combiner using a multilayer curved waveguide structure and output. The polarization states of the output signal photons are and The two idle photons first pass through a 2×2 thin-film lithium niobate optical switch 212, and then are input into and output from the polarization rotation-combiner using a multi-layer curved waveguide structure. When the 2×2 thin-film lithium niobate optical switch 212 works in the through state, the polarization states of the idle photons output from the output end of the polarization rotation-combiner are respectively and At this time, the polarization entangled state output by the chip is a two-way correlated two-photon state. and The polarization superposition of , where the phase It can be controlled by the electro-optical phase shifter 132. Controlled to 0 and , can be output as When the 2×2 thin-film lithium niobate optical switch 212 operates in the cross state, the polarization states of the idler photons output from the output end of the polarization rotation-combiner are and At this time, the polarization entangled state output by the chip is a two-way correlated two-photon state. and The polarization superposition of , where the phase It can be controlled by the electro-optical phase shifter 132. Controlled to 0 and , can be output as As a result, the chip can output four different polarization entangled states.

[0061] The following describes the implementation method of the chip 3 integrated with the polarization entangled quantum light source in the optical communication band provided by the present invention. The implementation method of the chip 3 integrated with the polarization entangled quantum light source in the optical communication band described below and the chip 3 integrated with the polarization entangled quantum light source in the optical communication band described above can correspond to each other.

[0062] Please refer to Figure 5 , Figure 5 A schematic flow chart of a method for realizing a chip-integrated polarization entangled quantum light source in an optical communication band provided by the present invention.

[0063] The present invention also provides a method for implementing a polarization entangled quantum light source integrated into a chip 3 in an optical communication band, which is implemented using the above-mentioned polarization entangled quantum light source integrated into a chip 3 in an optical communication band. The specific process is as follows: 501: generating a correlated two-photon state by a correlated two-photon state generating unit 1; the correlated two-photon state includes a polarization state of a first signal photon wave packet, a polarization state of a second signal photon wave packet, a polarization state of a first idler photon wave packet, and a polarization state of a second idler photon wave packet; 502: The polarization state of the second signal photon wave packet is rotated by the first polarization rotation-combiner 221, and then orthogonally polarized superposed with the polarization state of the first signal photon wave packet; the selected polarization state is determined by the optical switch 21 based on its own working state; the selected polarization state is the polarization state selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; the selected polarization state is rotated by the second polarization rotation-combiner 222, and then orthogonally polarized superposed with the unselected polarization state; finally four polarization entangled states are generated; the unselected polarization state is the polarization state that is not selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chip-integrated polarization entangled quantum light source in the optical communication band, characterized in that: It includes a correlated two-photon state generating unit and a polarization superposition unit which are connected in sequence and integrated on the same chip; The correlated two-photon state generating unit is used to generate correlated two-photon states; the correlated two-photon states include the polarization state of the first signal photon wave packet, the polarization state of the second signal photon wave packet, the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; The polarization superposition unit comprises an optical switch and two polarization rotation-beam combiners; the input end of the first polarization rotation-beam combiner serves as the first input end of the polarization superposition unit, one end of the optical switch serves as the second input end of the polarization superposition unit, and the other end of the optical switch is connected to the input end of the second polarization rotation-beam combiner; the output end of the first polarization rotation-beam combiner serves as the first output end of the polarization superposition unit, and the output end of the second polarization rotation-beam combiner serves as the second output end of the polarization superposition unit; The first polarization rotator-combiner is used to rotate the polarization state of the second signal photon wave packet and perform orthogonal polarization superposition with the polarization state of the first signal photon wave packet; the optical switch is used to determine the selected polarization state based on its own working state; the selected polarization state is the polarization state selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; the second polarization rotator-combiner is used to rotate the selected polarization state and perform orthogonal polarization superposition with the unselected polarization state; finally four polarization entangled states are generated; the unselected polarization state is the polarization state that is not selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet.

2. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 1, characterized in that: The correlated two-photon state generating unit comprises a pump beam splitter, two nonlinear optical waveguides, a waveguide phase shifter and two splitting filters; The first output end of the pump beam splitter is connected to the input end of the first nonlinear optical waveguide, the second output end of the pump beam splitter is connected to the input end of the second nonlinear optical waveguide, the output end of the first nonlinear optical waveguide is connected to the input end of the first optical splitter filter, the output end of the second nonlinear optical waveguide is connected to the input end of the waveguide phase shifter, the output end of the waveguide phase shifter is connected to the input end of the second optical splitter filter, the first output end of the first optical splitter filter is connected to the first input end of the first polarization rotation-combiner, the second output end of the first optical splitter filter is connected to the first input end of the optical switch, the first output end of the second optical splitter filter is connected to the second input end of the optical switch, and the second output end of the second optical splitter filter is connected to the second input end of the first polarization rotation-combiner; The pump beam splitter is used to split the pump laser so that the split light enters the first nonlinear optical waveguide and the second nonlinear optical waveguide respectively to stimulate spontaneous nonlinear optical processes and generate correlated two-photon pairs in the optical communication band; The waveguide phase shifter is used to change the phase of the associated two-photon pair in the optical communication band generated by the second nonlinear optical waveguide; The first optical splitter filter is used to output the polarization state of the first signal photon wave packet and the polarization state of the first idler photon wave packet; The second optical splitter filter is used to output the polarization state of the second signal photon wave packet and the polarization state of the second idler photon wave packet.

3. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 1, characterized in that: The chip is a silicon photonic integrated chip or a thin-film lithium niobate chip.

4. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 1, characterized in that: The optical switch is an MZI-type optical switch or a MEMS-type optical switch based on an adiabatic coupling structure.

5. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 1, characterized in that: The polarization rotator-beam combiner is a polarization rotator-beam combiner based on an asymmetric directional coupling structure or a polarization rotator-beam combiner based on an orthogonal polarization coupling structure.

6. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 2, characterized in that: The nonlinear optical waveguide is a waveguide supporting spontaneous four-wave mixing or a waveguide supporting spontaneous parametric down-conversion; the waveguide supporting spontaneous four-wave mixing includes silicon waveguide, silicon nitride waveguide, silicon dioxide waveguide and arsenic sulfide waveguide, and the waveguide supporting spontaneous parametric down-conversion includes periodically poled lithium niobate waveguide, periodically poled thin-film lithium niobate waveguide and periodically poled thin-film lithium tantalate waveguide.

7. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 2, characterized in that: The waveguide phase shifter is a thermo-optic phase shifter or an electro-optic phase shifter.

8. The chip-integrated polarization entangled quantum light source in the optical communication band according to claim 2, characterized in that: The spectroscopic filter is a bandpass filter based on a waveguide coupling structure, a bandpass filter based on a microring resonant cavity, or a bandpass filter based on AMZI.

9. The chip-integrated polarization entangled quantum light source in the optical communication band according to any one of claims 1 to 8, characterized in that: When the optical switch is in a through state, the selected polarization state is the polarization state of the second idler photon wave packet; when the optical switch is in a cross state, the selected polarization state is the polarization state of the first idler photon wave packet.

10. A method for realizing a chip-integrated polarization entangled quantum light source in an optical communication band, characterized in that: The chip-integrated polarization entangled quantum light source in the optical communication band of any one of claims 1 to 9 is used for realization, and the specific process is as follows: Generate a correlated two-photon state by a correlated two-photon state generating unit; the correlated two-photon state includes a polarization state of a first signal photon wave packet, a polarization state of a second signal photon wave packet, a polarization state of a first idler photon wave packet, and a polarization state of a second idler photon wave packet; The polarization state of the second signal photon wave packet is rotated by a first polarization rotation-combiner and then orthogonally polarized with the polarization state of the first signal photon wave packet; the selected polarization state is determined by an optical switch based on its own working state; the selected polarization state is a polarization state selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet; the selected polarization state is rotated by a second polarization rotation-combiner and then orthogonally polarized with an unselected polarization state; finally four polarization entangled states are generated; the unselected polarization state is a polarization state that is not selected from the polarization state of the first idler photon wave packet and the polarization state of the second idler photon wave packet.

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