Bidirectional pumping quantum light source system

Abstract

The invention discloses a bidirectional pumping quantum light source system which comprises a multimode interference coupler, two asymmetric Mach-Zehnder interferometers AMZI1 and AMZI2 and a quantum light source, the input end of the multimode interference coupler is used for receiving pumping light, and the output end of the multimode interference coupler is used for receiving the pumping light. The first output end of the multimode interference coupler is connected with the input end of the AMZI1, the first output end of the AMZI1 is connected with the first end of the quantum light source, the second output end of the multimode interference coupler is connected with the input end of the AMZI2, and the first output end of the AMZI2 is connected with the second end of the quantum light source, so that a Sagnac ring is formed. According to the bidirectional pumping quantum light source system disclosed by the invention, an asymmetric Mach-Zehnder interferometer with a filtering effect is embedded into a Saganc ring by utilizing the characteristic that pumping light, generated signals and idler frequency photons are different in frequency in a spontaneous four-wave mixing process, so that the extraction of the signals and the idler frequency photons in the Saganc ring is realized.

Description

Technical Field

[0001] The invention belongs to the field of quantum information technology, and in particular relates to a bidirectional pumping quantum light source system. Background Art

[0002] Single photons are important resources for quantum information technologies such as quantum sensing, quantum communication, and optical quantum computing. In recent years, the generation of single photons on a chip has become a research hotspot for quantum light sources due to its small size and high brightness.

[0003] On-chip single photons can be generated through spontaneous four-wave mixing (SFWM) in a helical waveguide or microring resonator (MRR). SFWM is a third-order nonlinear effect. When the pump light is input into a nonlinear medium, under the premise of energy conservation and phase matching, the two pump photons annihilate to generate a pair of photons at a new frequency, called the signal photon and the idler photon. Depending on whether the frequencies of the generated photons are the same, SFWM can be divided into two types: degenerate and non-degenerate. Degenerate SFWM requires two pump photons at different frequencies. p1 and ω p2 annihilation, generating a pair of signal idler photons of the same frequency ω s,i , satisfying ω p1 +ω p2 =ω s +ω i ; rather than degenerate SFWM requires the same frequency (ω p ) annihilate the two pump photons, generating a pair of signal photons with different frequencies ω at the center symmetry of the pump frequency. s and idler photonsω i , satisfying 2ω p =ω s +ω i In the helical single-photon source, single photons can be generated within the phase-matched bandwidth. In order to select single photons of a specific frequency, a filter is required. However, the MRR can only generate single photons at the resonant wavelength and does not require a filter. There are two common types of MRRs. One is the all-pass MRR, which consists of a microring and a straight waveguide coupled to the microring. The other is the up-down-down MRR, which consists of a microring and two straight waveguides coupled to the microring.

[0004] Currently, there have been extensive studies to enhance the performance of a single quantum light source, such as improving the structure of helices or microrings to increase the generation rate, prediction efficiency, and purity of single photons. However, most of these schemes consider exciting the quantum light source from one direction.

[0005] In order to enable optical quantum chips to handle complex tasks, it is necessary to expand the scale of the chip and integrate multiple indistinguishable quantum light sources, which requires the quantum light source to have strong scalability. However, the current quantum light source scheme based on unidirectional pumping faces certain challenges when expanding. For example, when using a helix to generate single photons, in order to ensure that the nonlinear interaction is strong enough, the length of the helix needs to be large enough. The silicon waveguide helix is ​​generally 1 to 2 cm long, resulting in a large chip area occupied by the helix; and although the MRR has a small area, it is sensitive to the manufacturing process and cannot guarantee the consistency of the performance of the prepared MRR, resulting in a decrease in the indistinguishability of the generated single photons, and the MRR needs to add a thermal phase shifter to make the resonant wavelengths between the MRRs consistent with each other, which increases the difficulty of adjustment.

[0006] In order to improve the scalability of quantum light sources, the quantum light source can be pumped in both clockwise and counterclockwise directions to generate photon pairs. The benefits of this bidirectional pumping scheme are: 1) One quantum light source structure plays the role of two light sources, which reduces the number of physical structures by half, thereby reducing the chip area of ​​the quantum light source. At the same time, when MRR is used as a single photon source, the number of required thermal phase shifters is reduced by half, reducing the control difficulty. 2) Single photons in two directions are generated in the same structure and are inherently indistinguishable, thereby improving the performance of the quantum light source.

[0007] To achieve bidirectional pumping, the quantum light source is generally placed in a Sagnac ring, that is, the two ports of the quantum light source are connected to the two outputs of a beam splitter, forming a ring structure. When the pump light enters the beam splitter from the input end, it will be divided into two beams that propagate clockwise and counterclockwise in the ring, and enter the quantum light source from two directions to stimulate the generation of single photons.

[0008] At present, for both helix and MRR single-photon sources, bidirectional pumping structures have been studied and implemented. For example, for helix single-photon sources, there have been reports on bidirectionally pumping helices by combining off-chip optical elements to produce frequency-degenerate photon pairs (npj Quantum Inf.5,90(2019)) and multiphoton quantum states (Light.Sci.&Appl.8,41(2019)); for microring single-photon sources, there have been experiments on realizing quantum beam splitters (Optica 2,779(2015)) and quantum frequency combs (npjQuantum Inf.9,57(2023)) through microrings. However, among the existing bidirectional pumping schemes, only the scheme using up-down microrings has achieved full integration, while the schemes using helices and all-pass microrings rely on the assistance of off-chip optical devices such as circulators. The reason is that the up-down MRR has two coupled straight waveguides, one of which is used for coupling input of pump light, and the other straight waveguide can be used for coupling output of single photons. Single photons generated in both directions can be extracted from the Sagnac ring through this waveguide. For helix and all-through microring single-photon sources, the generated single photons have no ports to help them be extracted from the Sagnac ring, so other optical devices are needed.

[0009] However, single photon sources based on helical wires and all-through microrings have been widely studied and are the two most commonly used quantum light source structures in photonic quantum chips. Therefore, an integrable bidirectional pumping scheme that is compatible with helical wires and all-through microrings is urgently needed to reduce the challenges of large-scale photonic quantum chips. Summary of the invention

[0010] The main purpose of the present invention is to provide a bidirectional pumping quantum light source system, which utilizes the characteristics of different frequencies of pump light and generated signal and idler photons in the spontaneous four-wave mixing process, embeds an asymmetric Mach-Zehnder interferometer (AMZI) with filtering effect into the Saganc ring, and realizes the extraction of signal and idler photons in the Sagnac ring.

[0011] Another object of the present invention is to provide a bidirectional pumping quantum light source system, which is suitable for the scenario of generating single photons using a helical waveguide or an all-pass microring resonator. This method improves the scalability of the quantum light source, can be easily integrated with subsequent optical quantum circuits, used to perform complex quantum tasks, and contributes to the development of large-scale optical quantum chips.

[0012] To achieve the above objectives, a bidirectionally pumped quantum light source system includes a multimode interference coupler, two asymmetric Mach-Zehnder interferometers AMZI1 and AMZI2, and a quantum light source, wherein:

[0013] The input end of the multimode interference coupler is used to receive the pump light, the first output end of the multimode interference coupler is connected to the input end of AMZI1 and the first output end of AMZI1 is connected to the first end of the quantum light source, the second output end of the multimode interference coupler is connected to the input end of AMZI2 and the first output end of AMZI2 is connected to the second end of the quantum light source, thereby forming a Sagnac ring;

[0014] AMZI1 is provided with a first single-photon output port and AMZI2 is provided with a second single-photon output port.

[0015] As a further preferred technical solution of the above technical solution, the working principle of the bidirectional pumping quantum light source system is:

[0016] When working, the frequency is ω p Or the frequency is ω p1 and ω p2 The pump light is input to the input end of the multimode interference coupler, and then the pump light is divided into two beams of equal power, and output from the first output end and the second output end port, respectively, and the two correspond to the clockwise and counterclockwise propagation directions in the Sagnac ring; Next, the clockwise and counterclockwise beams of light enter the input end of AMZI1 and the input end of AMZI2 respectively, and the phases of AMZI1 and AMZI2 are adjusted by the phase shifter, so that the pump light is output from the first output end of AMZI1 and the first output end of AMZI2 with the maximum efficiency and enters the quantum light source;

[0017] The two pump beams excite the quantum light source to produce single photons in the clockwise and counterclockwise directions respectively. Under the nonlinear effect of spontaneous four-wave mixing, the quantum light source produces single photons with a frequency of ω in the clockwise and counterclockwise directions. s The signal photon and frequency are ω i The idler photons, the residual pump light and the generated single photons in the two directions propagate in opposite directions. The single photons and pump light generated clockwise will enter AMZI2, while the single photons and pump light generated counterclockwise will enter AMZI1. At this time, for both the clockwise and counterclockwise directions, the pump light, signal and idler photons are input into the corresponding AMZI1 and AMZI2 from the same port. Therefore, AMZI1 and AMZI2 separate them to different output ports under the filtering action. The specific implementation is as follows:

[0018] The pump light will be output from the input end of AMZI1 and the input end of AMZI2, and then return to the multimode interference coupler. The pump light is in the Sagnac ring from beginning to end; however, the single photons propagating clockwise and counterclockwise will be output from the second single photon output port and the first single photon output port respectively, thereby separating from the pump light and leaving the Sagnac ring. At this time, the single photon generation and extraction of the bidirectional pumping quantum light source are completed.

[0019] As a further preferred technical solution of the above technical solution, the first single-photon output port and the second single-photon output port are respectively connected to the optical quantum circuit, so that the single photon is detected by the detector.

[0020] As a further preferred technical solution of the above technical solution, the quantum light source is a helical waveguide or an all-through micro-ring resonant cavity.

[0021] As a further preferred technical solution of the above technical solution, in order to ensure that the pump light and signal / idle photons are input into AMZI1 and AMZI2 from the same port and output from different ports, the free wave spectrum range of AMZI1 and AMZI2 is designed. Assuming that the target single photon frequency difference between the pump light and the quantum light source is δω, the free wave spectrum range of AMZI1 and AMZI2 is δω / (k+1 / 2), where k is a non-negative integer.

[0022] The beneficial effects of the present invention are:

[0023] 1) It provides a fully integrated solution for bidirectionally pumped helix waveguide and all-through microring single-photon sources, which helps to improve the scalability of quantum light sources and reduce the number of quantum light source structures required for large-scale optical quantum chips.

[0024] 2) The bidirectional pumping scheme of the present invention is not only applicable to basic helices and all-through microrings, but also to their improved structures to enhance the performance of quantum light sources.

[0025] 3) Bidirectional pumping improves the indistinguishability of single photons generated by nonlinear quantum light sources.

[0026] 4) The present invention separates single photons and pump light and extracts them into two waveguides outside the Sagnac ring, so that they can be easily connected to subsequent optical quantum lines to perform more complex functions, such as optical quantum computing and quantum communication.

[0027] 5) The present invention helps to reduce noise photons. First, the noise photons from the input waveguide will be filtered out by the AMZI to unused ports, so they will not enter the quantum light source. Secondly, the residual pump light that passes through the quantum light source returns to the MMI at the input end after passing through the AMZI, and will not enter the subsequent quantum circuit with the single photon, thus avoiding the possibility of exciting noise photons in the subsequent circuit.

[0028] 6) The present invention is applicable to a variety of nonlinear materials, including silicon, silicon nitride, etc., and will be helpful for the research and development of multi-system large-scale photonic quantum chips in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention.

[0030] Figure 2 It is a suitable type of quantum light source for the present invention, which can be a helical or all-through MRR. DETAILED DESCRIPTION

[0031] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0032] In the preferred embodiment of the present invention, those skilled in the art should note that the laser and the like involved in the present invention may be regarded as prior art.

[0033] Preferred embodiments.

[0034] like Figure 1-2 As shown, the present invention discloses a bidirectional pumping quantum light source system, including a (50:50) multimode interference coupler (MMI), two (2x2) asymmetric Mach-Zehnder interferometers AMZI1 and AMZI2, and a quantum light source, wherein:

[0035] The input end (in1 or in2) of the multimode interference coupler is used to receive pump light (generated by a laser), the first output end (o1) of the multimode interference coupler is connected to the input end (in3) of AMZI1 and the first output end (o4) of AMZI1 is connected to the first end of the quantum light source, the second output end (o2) of the multimode interference coupler is connected to the input end (in4) of AMZI2 and the first output end (o5) of AMZI2 is connected to the second end of the quantum light source, thereby forming a Sagnac ring;

[0036] AMZI1 is provided with a first single-photon output port (p1) and AMZI2 is provided with a second single-photon output port (p2).

[0037] Specifically, the working principle of the bidirectional pumping quantum light source system is:

[0038] When working, the frequency is ω p (non-degenerate SFWM case) or frequency ω p1 and ω p2The pump light (solid arrow) of (degenerate SFWM case) is input to the input end of the multimode interference coupler, and then the pump light is divided into two beams of equal power, and output from the first output end (o1) and the second output end (o2) ports, respectively, which correspond to the clockwise and counterclockwise propagation directions in the Sagnac ring; next, the clockwise and counterclockwise beams of light enter the input end (in3) of AMZI1 and the input end (in4) of AMZI2, respectively, and the phases of AMZI1 and AMZI2 are adjusted by the phase shifter, so that the pump light is output from the first output end (o4) of AMZI1 and the first output end (o5) of AMZI2 with maximum efficiency, and enters the quantum light source;

[0039] The two pump beams excite the quantum light source to produce single photons in the clockwise and counterclockwise directions respectively. Under the nonlinear effect of spontaneous four-wave mixing (SFWM), the quantum light source produces single photons with a frequency of ω in the clockwise and counterclockwise directions. s The signal photon (single photon) and the frequency ω i The idler photon (single photon) of the two-way residual pump light and the generated single photon propagate in opposite directions (the propagation direction of the single photon is indicated by the dotted arrow). The single photon (s 顺 i 顺 ) and pump light will enter AMZI2, while the single photons (s 逆 i 逆 ) and pump light will enter AMZI1; at this time, for both the forward and reverse directions, the pump light, signal and idler photons are input from the same port to the corresponding AMZI1 and AMZI2, so AMZI1 and AMZI2 separate them to different output ports under the filtering action, which is specifically implemented as follows:

[0040] The pump light will be output from the input end (in3) of AMZI1 and the input end (in4) of AMZI2, and then return to the multimode interference coupler (the residual pump light will transmit through AMZI and return to MMI). The pump light is always in the Sagnac ring; however, the single photons propagating clockwise and counterclockwise will be output from the second single photon output port (p2) and the first single photon output port (p1), respectively, thereby separating from the pump light and leaving the Sagnac ring. At this time, the single photon generation and extraction of the bidirectional pumping quantum light source are completed.

[0041] More specifically, the first single-photon output port (p1) and the second single-photon output port (p2) are respectively connected to the optical quantum circuit, so that the single photon is detected by the detector (and then performs complex optical quantum tasks, which can be applied to optical quantum computing, quantum communication and other fields).

[0042] Furthermore, the quantum light source is ( Figure 2 a) helical waveguide or ( Figure 2 b) All-pass microring resonator.

[0043] Furthermore, in order to make the pump light and the signal / idler photon input from the same port of AMZI1 and AMZI2 output from different ports, the free spectral range (FSR) of AMZI1 and AMZI2 is designed. Assuming that the frequency difference between the pump light and the target single photon generated by the quantum light source is δω, the free spectral range of AMZI1 and AMZI2 is δω / (k+1 / 2), where k is a non-negative integer (to determine the free spectral range of AMZI1 and AMZI2, assuming that the SFWM type is non-degenerate, the input pump light frequency is ω p , the frequencies of the signal photon and idler photon generated by the quantum light source are ω s and ω i , then the free wave spectrum range of AMZI1 and AMZI2 is 2|ω p -ω s(i) |; If the pump light and the generated photons are input into the corresponding AMZI1 and AMZI2 from the same port, they will be output from different ports of AMZI1 and AMZI2 respectively).

[0044] It is worth mentioning that the technical features such as lasers involved in the patent application of this invention should be regarded as prior art. The specific structure, working principle and possible control method and spatial arrangement method of these technical features can be selected according to the conventional methods in the field, and should not be regarded as the inventive point of this patent. This patent will not be further elaborated.

[0045] For those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bidirectionally pumped quantum light source system, characterized in that: It includes a multimode interference coupler, two asymmetric Mach-Zehnder interferometers AMZI1 and AMZI2, and a quantum light source, including: The input end of the multimode interference coupler is used to receive the pump light, the first output end of the multimode interference coupler is connected to the input end of AMZI1 and the first output end of AMZI1 is connected to the first end of the quantum light source, the second output end of the multimode interference coupler is connected to the input end of AMZI2 and the first output end of AMZI2 is connected to the second end of the quantum light source, thereby forming a Sagnac ring; AMZI1 is provided with a first single-photon output port and AMZI2 is provided with a second single-photon output port.

2. A bidirectional pumping quantum light source system according to claim 1, characterized in that: The working principle of the bidirectional pumping quantum light source system is: When working, the frequency is ω p Or the frequency is ω p1 and ω p2 The pump light is input to the input end of the multimode interference coupler, and then the pump light is divided into two beams of equal power, and output from the first output end and the second output end port, respectively, and the two correspond to the clockwise and counterclockwise propagation directions in the Sagnac ring; Next, the clockwise and counterclockwise beams of light enter the input end of AMZI1 and the input end of AMZI2 respectively, and the phases of AMZI1 and AMZI2 are adjusted by the phase shifter, so that the pump light is output from the first output end of AMZI1 and the first output end of AMZI2 with the maximum efficiency and enters the quantum light source; The two pump beams excite the quantum light source to produce single photons in the clockwise and counterclockwise directions respectively. Under the nonlinear effect of spontaneous four-wave mixing, the quantum light source produces single photons with a frequency of ω in the clockwise and counterclockwise directions. s The signal photon and frequency are ω i The idler photons, the residual pump light and the generated single photons in the two directions propagate in opposite directions. The single photons and pump light generated clockwise will enter AMZI2, while the single photons and pump light generated counterclockwise will enter AMZI1. At this time, for both the clockwise and counterclockwise directions, the pump light, signal and idler photons are input into the corresponding AMZI1 and AMZI2 from the same port. Therefore, AMZI1 and AMZI2 separate them to different output ports under the filtering action. The specific implementation is as follows: The pump light will be output from the input end of AMZI1 and the input end of AMZI2, and then return to the multimode interference coupler. The pump light is in the Sagnac ring from beginning to end; however, the single photons propagating clockwise and counterclockwise will be output from the second single photon output port and the first single photon output port respectively, thereby separating from the pump light and leaving the Sagnac ring. At this time, the single photon generation and extraction of the bidirectional pumping quantum light source are completed.

3. A bidirectional pumping quantum light source system according to claim 2, characterized in that: The first single-photon output port and the second single-photon output port are respectively connected to the optical quantum circuit, so that the single photon is detected by the detector.

4. A bidirectional pumping quantum light source system according to claim 1, characterized in that: The quantum light source is a helical waveguide or an all-through micro-ring resonator.

5. A bidirectional pumping quantum light source system according to claim 2, characterized in that: In order to ensure that the pump light and signal / idler photons are input into AMZI1 and AMZI2 from the same port and output from different ports, the free wave spectrum range of AMZI1 and AMZI2 is designed. Assuming that the frequency difference between the pump light and the target single photon generated by the quantum light source is δω, the free wave spectrum range of AMZI1 and AMZI2 is δω / (k+1 / 2), where k is a non-negative integer.

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