A chip-integrated polarization entangled quantum light source for optical communication band and its implementation method

Abstract

The present invention provides a chip-integrated polarization-entangled quantum light source for optical communication bands and an implementation method. The quantum light source includes a correlated two-photon state generation unit and a polarization superposition unit, which are integrated and connected in sequence on the same chip. The polarization superposition unit includes an optical switch and two polarization rotation-combiners. The correlated two-photon state generation unit generates 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 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 a selected polarization state based on its own operating state. The second polarization rotation-combiner rotates the selected polarization state and performs orthogonal polarization superposition with an unselected polarization state. The present invention achieves the generation of four polarization entangled states through on-chip photoelectric control.

Description

Technical Field

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

[0002] Quantum entanglement is a key resource in the field of quantum information and forms the basis for many quantum information applications, including quantum teleportation, quantum key distribution, and quantum computing. Therefore, quantum light sources that generate entangled photonic quantum states are crucial unit devices in optical quantum information systems. Currently, there are two main approaches to developing entangled quantum light sources.

[0003] The first method involves spontaneous parametric downconversion (SPDC) in a second-order nonlinear crystal. In this process, a pump photon annihilates, simultaneously generating a signal / idle photon pair. When a specific phase-matching technique is met, the collected signal / idle photons exhibit quantum correlation. In recent years, periodically polarized lithium niobate (PPLN) technology has been used to generate entangled two-photon pairs in the communication band. This polarization entanglement realization method requires only the nonlinear medium on the chip, necessitating numerous discrete optical components to form a complex external optical path. Furthermore, the polarization entanglement state cannot be manipulated through on-chip photoelectric control.

[0004] The second method relies on spontaneous four-wave mixing (SFWM) to generate correlated two-photon states in the communication band. In this process, two pump photons are annihilated, producing a pair of signal / idle photons with quantum correlation characteristics. Through appropriate optical path design, various quantum entangled states can be generated. These quantum light sources can be implemented using common third-order nonlinear waveguide media such as silica fiber and silicon waveguides, and the generated entangled photon pairs are located in the optical communication band, making them very suitable for integration with fiber optic communication networks. However, these schemes can only generate specific types of polarization-entangled two-photon states and cannot achieve arbitrary polarization-entangled two-photon state output through on-chip optoelectronic control.

[0005] Given that polarization is an important property of photons, polarization-entangled two-photon states have been widely used in quantum communication and quantum information processing research. High-quality generation of polarization-entangled quantum states has become an important topic in the development of chip-integrated entangled quantum light source devices. Summary of the Invention

[0006] This invention provides a chip-integrated polarization-entangled quantum light source and its implementation method for the optical communication band, thereby overcoming the limitation of existing technologies that cannot achieve arbitrary polarization-entangled two-photon state output through on-chip photoelectric control. This invention achieves the generation of four polarization-entangled states through on-chip photoelectric control.

[0007] This invention provides a chip-integrated polarization-entangled quantum light source for optical communication bands, comprising a correlated two-photon state generation unit and a polarization superposition unit connected sequentially on the same chip; the correlated two-photon state generation unit is used to generate correlated two-photon states; the correlated two-photon states include the polarization states of a first signal photon wave packet, a second signal photon wave packet, a first idler photon wave packet, and a second idler photon wave packet; the polarization superposition unit includes 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 second input end of the polarization superposition unit. The first output terminal of the polarization superposition unit and the output terminal of the second polarization rotation-beam combiner serve as the second output terminal of the polarization superposition unit. The first polarization rotation-beam combiner is used to rotate the polarization state of the second signal photon wave packet and then 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 operating state. The selected polarization state is a polarization state selected from the polarization states of the first idler photon wave packet and the second idler photon wave packet. The second polarization rotation-beam combiner is used to rotate the selected polarization state and then perform orthogonal polarization superposition with the unselected polarization state. Finally, four polarization entangled states are generated. The unselected polarization state is a polarization state that was not selected from the polarization states of the first idler photon wave packet and the second idler photon wave packet.

[0008] According to the present invention, a chip-integrated polarization-entangled quantum light source for optical communication bands includes a correlated two-photon state generation unit comprising a pump beamsplitter, two nonlinear optical waveguides, a waveguide phase shifter, and two beam splitters. The first output terminal of the pump beamsplitter is connected to the input terminal of the first nonlinear optical waveguide, and the second output terminal of the pump beamsplitter is connected to the input terminal of the second nonlinear optical waveguide. The output terminal of the first nonlinear optical waveguide is connected to the input terminal of the first beam splitter, the output terminal of the second nonlinear optical waveguide is connected to the input terminal of the waveguide phase shifter, and the output terminal of the waveguide phase shifter is connected to the input terminal of the second beam splitter. The first output terminal of the first beam splitter is connected to the first input terminal of the first polarization rotation-beam combiner, and the second output terminal of the first beam splitter is connected to the optical switch. The first input terminal of the first beam splitter is connected to the second input terminal of the optical switch, and the second output terminal of the second beam splitter is connected to the second input terminal of the first polarization rotation-beam combiner. The pump beam splitter is used to split the pump laser beam so that the split beams enter the first nonlinear optical waveguide and the second nonlinear optical waveguide respectively to excite spontaneous nonlinear optical processes and generate optical communication band correlated two-photon pairs. The waveguide phase shifter is used to change the phase of the optical communication band correlated two-photon pairs generated by the second nonlinear optical waveguide. The first beam splitter 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 beam splitter 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 the present invention, a chip-integrated polarization entangled quantum light source for the optical communication band is provided, wherein the chip is a silicon photonic integrated chip or a thin-film lithium niobate chip.

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

[0011] According to the present invention, a chip-integrated polarization entangled quantum light source for optical communication bands is provided, wherein 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.

[0012] According to the present invention, a chip-integrated polarization-entangled quantum light source for optical communication bands is provided, wherein 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 waveguides, silicon nitride waveguides, silicon dioxide waveguides, and arsenic sulfide waveguides, and the waveguide supporting spontaneous parametric down-conversion includes periodically polarized lithium niobate waveguides, periodically polarized thin-film lithium niobate waveguides, and periodically polarized thin-film lithium tantalate waveguides.

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

[0014] According to the present invention, a chip-integrated polarization entangled quantum light source for optical communication bands is provided, wherein the beam splitter is a bandpass filter based on a waveguide coupling structure, a bandpass filter based on a micro-ring resonator, or a bandpass filter based on AMZI.

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

[0016] This invention also provides a method for implementing a chip-integrated polarization-entangled quantum light source in the optical communication band. The method utilizes the aforementioned chip-integrated polarization-entangled quantum light source in the optical communication band. Specifically, the process involves: generating a correlated two-photon state through a correlated two-photon state generation unit; the correlated two-photon state includes 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; rotating the polarization state of the second signal photon wave packet using a first polarization rotation-beam combiner and then combining it with the polarization state of the first signal photon wave packet. The polarization states of the first photon wave packet are orthogonally superimposed; the selected polarization state is determined by an optical switch based on its own operating state; the selected polarization state is selected from the polarization states of the first idler photon wave packet and the second idler photon wave packet; the selected polarization state is rotated by a second polarization rotator-beam combiner and orthogonally superimposed with the unselected polarization state; finally, four polarization entangled states are generated; the unselected polarization state is the polarization state that was not selected from the polarization states of the first idler photon wave packet and the second idler photon wave packet.

[0017] This invention provides a chip-integrated polarization-entangled quantum light source and its implementation method for optical communication bands. The quantum light source includes a correlated two-photon state generation unit and a polarization superposition unit connected sequentially on the same chip. The polarization superposition unit includes an optical switch and two polarization rotation-beam combiners. The correlated two-photon state generation unit generates correlated two-photon states. The correlated two-photon states include the polarization states of a first signal photon wave packet, a second signal photon wave packet, a first idler photon wave packet, and a second idler photon wave packet. The first polarization rotation-beam 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 operating state. The second polarization rotation-beam combiner rotates the selected polarization state and performs orthogonal polarization superposition with the unselected polarization state. This invention achieves the generation of four polarization-entangled states through on-chip photoelectric control. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

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

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

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

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

[0023] Figure 5 This is a flowchart illustrating a method for implementing a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0024] Figure label:

[0025] 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 beam splitter filter; 142: Second beam splitter 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 Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] Please refer to Figure 1 , Figure 1 This is one of the schematic diagrams of a chip-integrated polarization entangled quantum light source for the optical communication band provided by the present invention.

[0028] This invention provides a chip-integrated polarization entangled quantum light source for the optical communication band, comprising a correlated two-photon state generation unit 1 and a polarization superposition unit 2 connected sequentially on the same chip 3; the correlated two-photon state generation unit 1 is used to generate correlated two-photon states; the correlated two-photon states include the polarization states of a first signal photon wave packet, a second signal photon wave packet, a first idler photon wave packet, and a second idler 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 first polarization rotation-beam combiner... The output of the first polarization superposition unit 221 serves as the first output of the polarization superposition unit 2, and the output of the second polarization rotation-beam combiner 222 serves as the second output of the polarization superposition unit 2. The first polarization rotation-beam combiner 221 is used to rotate the polarization state of the second signal photon wave packet and then 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 states of the first idler frequency photon wave packet and the second idler frequency photon wave packet. The second polarization rotation-beam combiner 222 is used to rotate the selected polarization state and then perform orthogonal polarization superposition with the unselected polarization state. Finally, four polarization entangled states are generated. The unselected polarization states are the polarization states that were not selected from the polarization states of the first idler frequency photon wave packet and the second idler frequency photon wave packet.

[0029] Please refer to Figure 2 , Figure 2 This is the second schematic diagram of a chip-integrated polarization entangled quantum light source for the optical communication band provided by the present invention.

[0030] In a preferred embodiment, the associated two-photon state generation unit 1 includes a pump beamsplitter 11, two nonlinear optical waveguides, a waveguide phase shifter 13, and two beam splitters. The first output of the pump beamsplitter 11 is connected to the input of the first nonlinear optical waveguide 121, and the second output of the pump beamsplitter 11 is connected to the input of the second nonlinear optical waveguide 122. The output of the first nonlinear optical waveguide 121 is connected to the input of the first beam splitter 141, the output of the second nonlinear optical waveguide 122 is connected to the input of the waveguide phase shifter 13, and the output of the waveguide phase shifter 13 is connected to the input of the second beam splitter 142. The first output of the first beam splitter 141 is connected to the first input of the first polarization rotation-beam combiner 221, and the second output of the first beam splitter 141 is connected to the optical switch 21. The first input terminal of the first beam splitter 142 is connected to the first output terminal of the second beam splitter 142, which is connected to the second input terminal of the optical switch 21. The second output terminal of the second beam splitter 142 is connected to the second input terminal of the first polarization rotation-combiner 221. The pump beam splitter 11 is used to split the pump laser beam so that the split beams enter the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122 respectively to excite spontaneous nonlinear optical processes and generate optical communication band correlated two-photon pairs. The waveguide phase shifter 13 is used to change the phase of the optical communication band correlated two-photon pairs generated by the second nonlinear optical waveguide 122. The first beam splitter 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 beam splitter 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.

[0031] 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. The quantum light source includes a correlated two-photon state generation unit 1 and a polarization superposition unit 2, which are integrated on the same chip 3 and directly connected.

[0032] The associated two-photon state generation 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 beam splitters (a first beam splitter 141 and a second beam splitter 142). After a pump laser of a specific polarization is coupled into the chip 3, it is first split into two beams by the pump beam splitter 11. These beams then enter the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122, respectively, to excite spontaneous nonlinear optical processes, including spontaneous four-wave mixing or spontaneous parametric down-conversion, generating photon pairs for a specific polarization communication band. The photon pair contains two photons with different frequencies; the lower-frequency photon is called the signal photon, and the higher-frequency photon is called the idler photon, abbreviated as s and i, respectively. The waveguide phase shifter 13 is connected to the second nonlinear optical waveguide 122 to change the phase of the signal photon and the idler photon generated in the second nonlinear optical waveguide 122. The wave packets of signal photons and idler photons of a specific frequency generated in each waveguide are selected by the beam splitter connected to that waveguide and output to the two filter output ports with specific polarization states, entering the polarization superposition unit 2. Without loss of generality, the specific polarization state of the output wave packets at each port can be defined as horizontal polarization, abbreviated as H. Therefore, the polarization states of the signal photons and idler photons generated in the first nonlinear optical waveguide 121 can be denoted as: and The corresponding correlated two-photon state can be denoted as The polarization states of the signal photons and idler photons generated in the second nonlinear optical waveguide 122 can be denoted as: and The corresponding correlated two-photon state can be denoted as .

[0033] The polarization superposition unit 2 may include two polarization rotation-combiners (first polarization rotation-combiner 221 and second polarization rotation-combiner 222) and a 2×2 optical switch 21. The polarization state of the first signal photon wave packet output from the first beam splitter 141 of the associated two-photon state generation unit 1 is input to the first input terminal of the first polarization rotation-combiner 221 with H polarization. The polarization state of the second signal photon wave packet output from the second beam splitter 142 of the associated two-photon state generation unit 1 is input to the second input terminal of the first polarization rotation-combiner 221 with H polarization. The first polarization rotation-combiner 221 rotates the polarization state of the second signal photon wave packet by 90 degrees, making it vertically polarized, abbreviated as V, and then performs orthogonal polarization superposition with the polarization state of the first signal photon wave packet before outputting it from the output port of the first polarization rotation-combiner 221. Thus, the polarization states of the signal photons output from the output terminal of the first polarization rotation-combiner 221 are respectively and The polarization state of the first idler photon wave packet output from the first beam-splitting filter 141 of the associated two-photon state generation unit 1 is input to the first input terminal of the 2×2 optical switch 21 with H polarization. The polarization state of the second idler photon wave packet output from the second beam-splitting filter 142 of the associated two-photon state generation unit 1 is input to the second input terminal of the 2×2 optical switch 21 with 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 terminal of the second polarization rotation-combiner 222).

[0034] If the 2×2 optical switch 21 operates in through mode, in the second polarization rotation-combiner 222, the polarization state of the second idler photon wave packet will be rotated 90 degrees, becoming V-polarized, and then orthogonally superimposed with the polarization state of the first idler photon wave packet before being output from the output port of the second polarization rotation-combiner 222. Therefore, the polarization states of the idler photons output from the output end of the second polarization rotation-combiner 222 are respectively... and At this point, the polarization entangled state output by the chip is a two-path correlated two-photon state. and The polarization superposition can be written as: Phase It can be controlled by waveguide phase shifter 13, by... Regulation to 0 and It can output in the form of The polarization entangled state.

[0035] If the 2×2 optical switch 21 operates in the cross state, in the second polarization rotation-combiner 222, the polarization state of the first idler photon wave packet will be rotated by 90 degrees, becoming V-polarized, and then orthogonally superimposed with the polarization state of the second idler photon wave packet before being output from the output port of the second polarization rotation-combiner 222. Therefore, the polarization states of the idler photons output from the output end of the second polarization rotation-combiner 222 are respectively... and At this point, the polarization entangled state output by the chip is a two-path correlated two-photon state. and The polarization superposition can be written as: Phase It can be controlled by waveguide phase shifter 13, by... Regulation to 0 and It can output in the form of The polarization entangled states. Thus, this optical path can realize the generation of all four polarization entangled Bell states.

[0036] In the above introduction, the lower-frequency photon in a photon pair is called the signal photon, and the higher-frequency photon is called the idler photon, abbreviated as s and i respectively. The description above still holds true when the higher-frequency photon in a photon pair is called the signal photon and the lower-frequency photon is called the idler photon.

[0037] This invention supports the generation of all four polarization-entangled Bell states by adjusting the waveguide phase shifter 13 on chip 3 and changing the operating state of the 2×2 optical switch 21. All unit devices in this invention are integrated on the same chip 3, eliminating the need for external polarization control devices to switch between polarization-entangled Bell states. This invention can be used for both third-order nonlinear waveguide chips 3 supporting spontaneous four-wave mixing quantum light sources and second-order nonlinear waveguide chips 3 supporting spontaneous parametric down-conversion.

[0038] In a preferred embodiment, chip 3 is a silicon photonic integrated chip 31 or a thin-film lithium niobate chip 32.

[0039] In this embodiment, a silicon photonic integrated chip 31 can be used as the basic platform. Silicon material has excellent optical properties, high refractive index contrast, and mature micro-nano fabrication technology, which can realize highly integrated and high-performance optical devices.

[0040] Of course, a thin-film lithium niobate chip 32 can also be used as the basic platform. Lithium niobate has excellent electro-optic effects and nonlinear optical properties, which can realize efficient optical modulation and photon pair generation.

[0041] As a preferred embodiment, the optical switch 21 is an MZI-based optical switch or a MEMS-based optical switch based on an adiabatic coupling structure.

[0042] In this embodiment, the optical switch 21 can be an MZI (Mach-Zehnder Interferometer) type optical switch or a MEMS (Micro-Electro-Mechanical Systems) type optical switch based on an adiabatic coupling structure.

[0043] For example, the optical switch 21 can be a Mach-Zehnder interferometer 211. The Mach-Zehnder interferometer 211 consists of two beam splitters and two mirrors, forming an interference loop. The input light is split into two beams by the first beam splitter, each passing through one of the two arms, and then recombined 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.

[0044] Of course, the optical switch 21 can also be a thin-film lithium niobate optical switch 212. The thin-film lithium niobate optical switch 212 has excellent electro-optic 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.

[0045] As a preferred embodiment, 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.

[0046] In this embodiment, the polarization rotation-beam combiner can be an asymmetric directional coupler structure. An asymmetric directional coupler structure consists of two waveguides, one with a wider width than the other, forming an asymmetric structure. When light enters the narrow waveguide from the wide waveguide, the polarization state of the light rotates due to the change in the mode field distribution.

[0047] The polarization rotation-beam combiner can be based on an orthogonal polarization coupling structure, which has high efficiency, high integration and wide band characteristics.

[0048] Of course, polarization rotation-beam combiners can also be made using multi-layer curved waveguide structures. A multi-layer curved waveguide polarization rotation-beam combiner consists of multiple curved waveguides, with the bending radius and interlayer spacing of each waveguide precisely designed to achieve polarization state rotation and beam combining of light. When light propagates in a curved waveguide, its polarization state rotates due to changes in the mode field distribution.

[0049] As a preferred embodiment, the nonlinear optical waveguide is a waveguide that supports spontaneous four-wave mixing or a waveguide that supports spontaneous parametric down-conversion; waveguides that support spontaneous four-wave mixing include silicon waveguides, silicon nitride waveguides, silicon dioxide waveguides, and arsenic sulfide waveguides, and waveguides that support spontaneous parametric down-conversion include periodically polarized lithium niobate waveguides, periodically polarized thin-film lithium niobate waveguides, and periodically polarized thin-film lithium tantalate waveguides.

[0050] In this embodiment, the silicon waveguide, as a nonlinear optical waveguide supporting spontaneous four-wave mixing (SFWM), has a high nonlinear coefficient and high refractive index contrast, which can effectively enhance the interaction between light and light, thereby improving the generation efficiency of correlated two-photon states.

[0051] Periodically polarized lithium niobate waveguides serve as nonlinear optical waveguides supporting spontaneous parametric down-conversion (SPDC). The periodic polarization structure effectively enhances the nonlinear effects of the waveguide, improving the generation efficiency and coherence of photon pairs.

[0052] In a preferred embodiment, the waveguide phase shifter 13 is a thermo-optical phase shifter 131 or an electro-optical phase shifter 132.

[0053] As a preferred embodiment, the optical splitter 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.

[0054] In a preferred embodiment, when the optical switch 21 is in the through state, the selected polarization state is the polarization state of the second idler photon wave packet; when the optical switch 21 is in the cross state, the selected polarization state is the polarization state of the first idler photon wave packet.

[0055] Please refer to Figure 3 , Figure 3 The third schematic diagram of a chip-integrated polarization entangled quantum light source for the optical communication band provided by the present invention.

[0056] In this embodiment, the beam splitter can be a bandpass filter based on a waveguide coupling structure, a bandpass filter based on a micro-ring resonator, or a bandpass filter based on an AMZI (Asymmetric Mach-Zehnder Interferometer).

[0057] The quantum light source is fabricated on a silicon-on-insulator (SOI) substrate using conventional silicon photonic integrated circuit (SIC) technology. It consists of 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 employs a 1×2 multimode interferometer. The nonlinear optical waveguides (first nonlinear optical waveguide 121 and second nonlinear optical waveguide 122) are single-mode silicon waveguides, generating correlated two-photon pairs through spontaneous four-wave mixing (SFWM) within the silicon waveguides. The waveguide phase shifter 13 is a thermo-optical phase shifter 131 connected to the silicon waveguide, enabling phase modulation of the correlated two-photon pairs generated in the second nonlinear optical waveguide 122. The beam splitter filters (first beam splitter 141 and second beam splitter 142) are cascaded narrowband bandpass filters 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 (first polarization rotation-combiner 221 and second polarization rotation-combiner 222) adopts an asymmetric directional coupler structure with a combination of wide and narrow polarizations.

[0058] In practical applications, After the pump laser in the optical communication band is coupled into chip 3 via a quartz fiber, it is first split into two beams with equal success rate by a 1×2 multimode interferometer. These beams are then input into a single-mode silicon waveguide to excite a spontaneous four-wave mixing process, generating correlated two-photon pairs. The phase of the correlated two-photon pairs generated in the second nonlinear optical waveguide 122 (single-mode silicon waveguide) can be modulated by a thermo-optical phase shifter 131. Thus, the correlated two-photon states generated in the single-mode silicon waveguide are respectively... and Subsequently, the correlated two-photon pair is input to a cascaded narrowband bandpass filter using a grating-assisted directional coupler structure to extract the signal / idle photons of the corresponding band. Then, the two signal photons are input to a polarization rotation-beam combiner using an asymmetric directional coupler structure and output, with the polarization states of the output signal photons being... and The two idler photons first pass through a 2×2 Mach-Zehnder interferometer 211, and are then input into a polarization rotation-combiner employing an asymmetric directional coupler structure before being output. When the 2×2 Mach-Zehnder interferometer 211 operates in the through state, the polarization states of the idler photons output from the output terminal of the polarization rotation-combiner 222 are respectively... and At this point, the polarization entangled state output by the chip is a two-path correlated two-photon state. and The polarization superposition can be written as: Phase It can be controlled by the thermo-optical phase shifter 131, by... Regulation to 0 and It can output in the form of The polarization entangled states; when the 2×2 Mach-Zehnder interferometer 211 operates in the cross state, the polarization states of the idler photons output from the polarization rotation-beam combiner are respectively and At this point, the polarization entangled state output by the chip is a two-path correlated two-photon state. and The polarization superposition can be written as: Phase It can be controlled by the thermo-optical phase shifter 131, by... Regulation to 0 and It can output in the form of The polarization entangled states. Therefore, the chip can output four different polarization entangled states.

[0059] Please refer to Figure 4 , Figure 4 The fourth schematic diagram of a chip-integrated polarization entangled quantum light source for the optical communication band provided by the present invention.

[0060] In this embodiment, the quantum light source uses a thin-film lithium niobate substrate and is fabricated using a thin-film lithium niobate chip 32 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 uses a 1×2 multimode interferometer. The nonlinear optical waveguide uses a periodically polarized single-mode thin-film lithium niobate waveguide, referred to as the first nonlinear optical waveguide 121 and the second nonlinear optical waveguide 122, respectively. Correlated two-photon pairs are generated through spontaneous parametric down-conversion (SPDC) in the periodically polarized single-mode thin-film lithium niobate waveguide. The waveguide phase shifter 13 is an electro-optic phase shifter 132 connected to the waveguide to achieve phase modulation of the correlated two-photon pairs generated in the second waveguide. The beam splitter filter uses a narrowband bandpass filter with a micro-ring resonant cavity structure. In the polarization superposition unit 2, the 2×2 optical switch 21 uses a 2×2 thin-film lithium niobate optical switch 212. The polarization rotation-beam combiner uses a polarization rotation-beam combiner with a multilayer curved waveguide structure.

[0061] In practical applications, after the pump laser is coupled into chip 3 via a quartz fiber, it is first split into two beams with equal success rates by a 1×2 multimode interferometer. These beams are then input into a periodically polarized single-mode thin-film lithium niobate waveguide to excite spontaneous parametric downconversion and generate correlated two-photon pairs. The phase of the correlated two-photon pairs generated by the second nonlinear optical waveguide 122 can be modulated by an electro-optic 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 to a narrowband bandpass filter employing a microring resonator structure to extract the signal / idle photons of the corresponding band. Then, the two signal photons are input into a polarization rotator-beam combiner employing a multi-layered curved waveguide structure and output, with the polarization states of the output signal photons being... and The two idler photons first pass through a 2×2 thin-film lithium niobate optical switch 212, and are then input into a polarization rotation-combiner employing a multilayer curved waveguide structure before being output. When the 2×2 thin-film lithium niobate optical switch 212 operates in the through state, the polarization states of the idler photons output from the polarization rotation-combiner are respectively... and At this point, the polarization entangled state output by the chip is a two-path correlated two-photon state. and The polarization superposition can be written as: Phase It can be controlled by the electro-optic phase shifter 132, by... Regulation to 0 and It can output in the form of The polarization entangled states; when the 2×2 thin-film lithium niobate optical switch 212 operates in the crossover state, the polarization states of the idler photons output from the polarization rotation-beam combiner output terminal are respectively and At this point, the polarization entangled state output by the chip is a two-path correlated two-photon state. and The polarization superposition can be written as: Phase It can be controlled by the electro-optic phase shifter 132, by... Regulation to 0 and It can output in the form of The polarization entangled states. Therefore, the chip can output four different polarization entangled states.

[0062] The following describes the implementation method of the chip 3 integrated polarization entangled quantum light source in the optical communication band provided by the present invention. The implementation method of the chip 3 integrated polarization entangled quantum light source in the optical communication band described below can be referred to in correspondence with the above-described chip 3 integrated polarization entangled quantum light source in the optical communication band.

[0063] Please refer to Figure 5 , Figure 5 This is a flowchart illustrating a method for implementing a chip-integrated polarization entangled quantum light source in the optical communication band provided by the present invention.

[0064] This invention also provides a method for implementing a chip-3 integrated polarization entangled quantum light source in the optical communication band. The method utilizes the aforementioned chip-3 integrated polarization entangled quantum light source in the optical communication band. The specific process is as follows:

[0065] 501: A correlated two-photon state is generated by the correlated two-photon state generation unit 1; the correlated 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 photon wave packet, and the polarization state of the second idler photon wave packet;

[0066] 502: The polarization state of the second signal photon wave packet is rotated by the first polarization rotation-beam combiner 221 and orthogonally superimposed 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 states of the first idler frequency photon wave packet and the second idler frequency photon wave packet; the selected polarization state is rotated by the second polarization rotation-beam combiner 222 and orthogonally superimposed with the unselected polarization state; finally, four polarization entangled states are generated; the unselected polarization states are the polarization states not selected from the polarization states of the first idler frequency photon wave packet and the second idler frequency photon wave packet.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate 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 for optical communication bands, characterized in that, This includes a correlated two-photon state generation unit and a polarization superposition unit connected sequentially on the same chip; The associated two-photon state generation unit is used to generate associated two-photon states; the associated 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 includes 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 rotation-beam combiner is used to rotate the polarization state of the second signal photon wave packet and then orthogonally superimpose it 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 operating state; the selected polarization state is a polarization state selected from the polarization states of the first idler photon wave packet and the second idler photon wave packet; the second polarization rotation-beam combiner is used to rotate the selected polarization state and then orthogonally superimpose it with the unselected polarization state; finally, four polarization entangled states are generated; the unselected polarization state is a polarization state that was not selected from the polarization states of the first idler photon wave packet and the second idler photon wave packet.

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

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

5. The chip-integrated polarization-entangled quantum light source for the optical communication band according to claim 1, characterized in that, 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.

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

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

8. The chip-integrated polarization-entangled quantum light source for the optical communication band according to claim 2, characterized in that, The beam splitter 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.

9. The chip-integrated polarization-entangled quantum light source for the optical communication band according to any one of claims 1 to 8, characterized in that, When the optical switch is in the through state, the selected polarization state is the polarization state of the second idler photon wave packet; when the optical switch is in the 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 the optical communication band, characterized in that, The process is as follows: A chip-integrated polarization-entangled quantum light source for the optical communication band as described in any one of claims 1 to 9 is used. A correlated two-photon state is generated by a correlated two-photon state generation unit; the correlated two-photon state includes 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 state of the second signal photon wave packet is rotated by a first polarization rotation-beam combiner and then orthogonally superimposed with the polarization state of the first signal photon wave packet. A selected polarization state is determined by an optical switch based on its own operating state. The selected polarization state is chosen from the polarization states of the first and second idler photon wave packets. The selected polarization state is rotated by a second polarization rotation-beam combiner and then orthogonally superimposed with an unselected polarization state. Finally, four polarization entangled states are generated. The unselected polarization states are those not chosen from the polarization states of the first and second idler photon wave packets.

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