A bidirectional pumped quantum light source system

Abstract

The application 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. The first output end of the multimode interference coupler is connected with the input end of the AMZI1, and 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 as to form a Sagnac ring. The bidirectional pumping quantum light source system disclosed by the application utilizes the characteristics that the frequencies of pumping light and generated signal and idler photons are different in the spontaneous four-wave mixing process, embeds the asymmetric Mach-Zehnder interferometer with filtering effect into the Sagnac ring, and realizes the extraction of signal and idler photons in the Sagnac ring.

Description

Technical Field

[0001] This invention belongs to the field of quantum information technology, and specifically relates to a bidirectional pumped quantum light source system. Background Technology

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

[0003] On-chip single-photon generation can be achieved through spontaneous four-wave mixing (SFWM) in a helical waveguide or microring resonator (MRR). SFWM is a third-order nonlinear effect. When pump light is input into a nonlinear medium, under the premise of energy conservation and phase matching, two pump photons annihilate, generating a pair of photons at new frequencies, called the signal photon and the idler photon, respectively. Based on whether the generated photons have the same frequency, SFWM can be divided into degenerate and non-degenerate types. Degenerate SFWM requires two pump photons ω at different frequencies. p1 and ω p2 Annihilation produces a pair of signal idler photons ω of the same frequency. s,i , satisfying ω p1 +ω p2 =ω s +ω i Non-degenerate SFWM requires the same frequency (ω). p The annihilation of two pump photons generates a pair of signal photons ω of different frequencies at a point symmetrical to the pump frequency center. s And idle frequency photon ω i Satisfying 2ω p =ω s +ω i In a spiral single-photon source, single photons can be generated within the phase-matched bandwidth. A post-filter is needed to select single photons at a specific frequency. In contrast, a MRR (Medium-Range Resonant Source) can only generate single photons at the resonant wavelength and does not require a post-filter. There are two common types of MRRs: an all-pass MRR, consisting of a microring and a straight waveguide coupled to the microring; and a top-down MRR, consisting of a microring and two straight waveguides coupled to the microring.

[0004] Currently, extensive research has been conducted to enhance the performance of individual quantum light sources, such as by 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 only one direction.

[0005] To enable quantum chips to handle complex tasks, it is necessary to scale up the chip and integrate multiple indistinguishable quantum light sources, requiring strong scalability of the quantum light sources. However, current quantum light source schemes based on unidirectional pumping face certain challenges when scaling up. For example, when using helices to generate single photons, a sufficiently long helix is ​​required to ensure strong nonlinear interactions. Silicon waveguide helices are typically 1–2 cm long, resulting in a large chip area occupied by the helix. While MRRs have a smaller area, they are sensitive to manufacturing processes, making it impossible to guarantee consistent performance among the fabricated MRRs. This reduces the indistinguishability of the generated single photons. Furthermore, MRRs require the addition of thermal phase shifters to ensure that the resonant wavelengths of the MRRs are consistent, increasing the difficulty of adjustment.

[0006] To improve the scalability of quantum light sources, photon pairs can be generated by simultaneously pumping the quantum light source in both clockwise and counterclockwise directions. The advantages of this bidirectional pumping scheme are: 1) A single quantum light source structure functions as two light sources, halving the number of physical structures and thus reducing the chip area ratio of the quantum light source. Furthermore, when using MRR as a single photon source, the number of required thermal phase shifters is halved, reducing control complexity. 2) Single photons from both directions are generated within the same structure, possessing inherent indistinguishability, thereby improving the performance of the quantum light source.

[0007] To achieve bidirectional pumping, the quantum light source is typically placed within a Sagnac ring, where 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, it is split into two beams that propagate clockwise and counterclockwise within the ring, and then enter the quantum light source from both directions to excite single photons.

[0008] Currently, bidirectional pumping structures have been studied and implemented for both helical and MRR single-photon sources. For example, for helical single-photon sources, there have been reports of bidirectionally pumping helices to generate frequency degenerate photon pairs (npj Quantum Inf. 5, 90 (2019)) and multiphoton quantum states (Light. Sci. & Appl. 8, 41 (2019)) by combining under-chip optical elements; for microring single-photon sources, there have been experiments on realizing quantum beam splitters (Optica 2, 779 (2015)) and quantum frequency combs (npj Quantum Inf. 9, 57 (2023)) using microrings. However, among the existing bidirectional pumping schemes, only the scheme using top-down and bottom-up microrings has achieved full integration, while the schemes using helices and all-through microrings rely on the assistance of under-chip optical devices such as circulators. The reason for this is that the uplink / downlink MRR has two coupled straight waveguides. One straight waveguide is used for the coupled input of the pump light, and the other straight waveguide can be used for the coupled output of single photons. The bidirectional single photons can be extracted from the Sagnac ring through this waveguide. However, for spiral and all-through micro-ring single-photon sources, the generated single photons do not have a port to help them be extracted from the Sagnac ring, so other optical devices are required.

[0009] However, single-photon sources based on helices and all-through microrings are widely studied and are the two most commonly used quantum light source structures in optical quantum chips. Therefore, there is an urgent need for an integrable bidirectional pumping scheme compatible with both helices and all-through microrings to reduce the challenges of large-scale optical quantum chips. Summary of the Invention

[0010] The main objective of this invention is to provide a bidirectional pumped quantum light source system that utilizes the characteristic that the pump light and the generated signal and idler photons have different frequencies during the spontaneous four-wave mixing process. An asymmetric Mach-Zehnder interferometer (AMZI) with filtering function is embedded in the Saganc ring to extract the signal and idler photons in the Saganc ring.

[0011] Another objective of this invention is to provide a bidirectional pumped quantum light source system suitable for scenarios where single photons are generated using helical waveguides or all-through micro-ring resonators. This method improves the scalability of the quantum light source, allowing for easy integration with subsequent optical quantum circuits to perform complex quantum tasks, and contributing to the development of large-scale optical quantum chips.

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

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

[0014] AMZI1 has a first single-photon output port and AMZI2 has a second single-photon output port.

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

[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 of the multimode interference coupler, and then split into two beams of equal power, which are output from the first and second output ports respectively. The two beams propagate in clockwise and counterclockwise directions within the Sagnac ring. Next, the clockwise and counterclockwise beams enter the input ports of AMZI1 and AMZI2 respectively. The phase of AMZI1 and AMZI2 is adjusted by a phase shifter so that the pump light is output from the first output port of AMZI1 and the first output port of AMZI2 with maximum efficiency and enters the quantum light source.

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

[0018] The pump light will be output from the input terminals of AMZI1 and AMZI2, and then return to the multimode interference coupler. The pump light is always within the Sagnac ring. However, the clockwise and counterclockwise propagating single photons will be output from the second single photon output port and the first single photon output port, respectively, thus separating from the pump light and leaving the Sagnac ring. At this point, the single photon generation and extraction of the bidirectional pumped quantum light source are completed.

[0019] As a further preferred embodiment 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 can be detected by the detector.

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

[0021] As a further preferred technical solution to the above technical solution, in order to ensure that when the pump light and the signal / idle photon are input from the same port to AMZI1 and AMZI2, they will be output from different ports, the free 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 spectrum range of AMZI1 and AMZI2 is δω / (k+1 / 2), where k is a non-negative integer.

[0022] The beneficial effects of this invention are as follows:

[0023] 1) It provides a fully integrated solution for bidirectional pumped helical waveguides and all-pass micro-ring 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 applicable not only to basic spirals 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) This invention separates the single photon and the pump light and extracts them into two waveguides outside the Sagnac ring, so that they can be easily connected to subsequent optical quantum circuits to perform more complex functions, such as optical quantum computing and quantum communication.

[0027] 5) This invention helps reduce noise photons. First, noise photons from the input waveguide are filtered out by the AMZI and directed to unused ports, thus preventing them from entering the quantum light source. Second, the residual pump light from the quantum light source returns to the MMI at the input end after passing through the AMZI, and does not enter subsequent quantum circuits with single photons, avoiding the possibility of exciting noise photons in subsequent circuits.

[0028] 6) This invention is applicable to a variety of nonlinear materials, including silicon and silicon nitride, and is helpful for the future development of large-scale multi-system optical quantum chips. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the present invention.

[0030] Figure 2 This is the applicable type of quantum light source for the present invention, which can be a spiral or all-through MRR. Detailed Implementation

[0031] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0032] In the preferred embodiments of the present invention, those skilled in the art should note that the lasers and the like involved in the present invention can be considered as prior art.

[0033] Preferred embodiment.

[0034] like Figure 1-2 As shown, this invention discloses a bidirectional pumped quantum light source system, comprising one (50:50) multimode interference coupler (MMI), two (2x2) asymmetric Mach-Zend interferometers AMZI1 and AMZI2, and one quantum light source, wherein:

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

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

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

[0038] When working, the frequency is ω p (Non-degenerate SFWM case) or frequency ω p1 and ω p2(In the case of degenerate SFWM) The pump light (solid arrow) is input to the input of the multimode interference coupler, and then the pump light is split into two beams of equal power, which are output from the first output port (o1) and the second output port (o2) respectively. The two beams have clockwise and counterclockwise propagation directions within the Sagnac ring. Next, the clockwise and counterclockwise beams enter the input ports (in3) of AMZI1 and (in4) of AMZI2 respectively. The phase of AMZI1 and AMZI2 is adjusted by the phase shifter so that the pump light is output from the first output port (o4) of AMZI1 and the first output port (o5) of AMZI2 with maximum efficiency and enters the quantum light source.

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

[0040] The pump light will be output from the input terminals (in3) of AMZI1 and (in4) of AMZI2, and then return to the multimode interference coupler (the residual pump light will pass through AMZI and return to MMI). The pump light is always within the Sagnac ring. However, the clockwise and counterclockwise propagating single photons will be output from the second single photon output port (p2) and the first single photon output port (p1) respectively, thus separating from the pump light and leaving the Sagnac ring. At this point, the single photon generation and extraction of the bidirectional pumped 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 can be detected by the detector (and then perform complex optical quantum tasks, which can be applied to fields such as optical quantum computing and quantum communication).

[0042] Furthermore, quantum light sources are ( Figure 2 (as shown in a) helical waveguide or ( Figure 2 (b) is an all-through micro-ring resonator.

[0043] Furthermore, to ensure that pump light and signal / idle photons, when input from the same port to AMZI1 and AMZI2, will output from different ports, the free spectral range (FSR) of AMZI1 and AMZI2 is designed. Assuming the frequency difference between the pump light and the target single photon generated by the quantum light source is δω, the FSR of AMZI1 and AMZI2 is δω / (k+1 / 2), where k is a non-negative integer. (To determine the FSR of AMZI1 and AMZI2, it is assumed that the SFWM type is non-degenerate, and the input pump light frequency is ω.) p The frequencies of the signal photon and the idler photon generated by the quantum light source are ω and ω, respectively. 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 from the same port to the corresponding AMZI1 and AMZI2, then 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 this patent application should be regarded as prior art. The specific structure, working principle, and possible control methods and spatial arrangement of these technical features can be adopted using conventional choices in the field, and should not be regarded as the inventive point of this patent. This patent will not be further elaborated in detail.

[0045] For those skilled in the art, 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. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A bidirectional pumped quantum light source system, characterized in that, It includes one multimode interference coupler, two asymmetric Mach-Zend interferometers AMZI1 and AMZI2, and one quantum light source, wherein: The input of the multimode interference coupler is used to receive pump light. The first output of the multimode interference coupler is connected to the input of AMZI1 and the first output of AMZI1 is connected to the first end of the quantum light source. The second output of the multimode interference coupler is connected to the input of AMZI2 and the first output of AMZI2 is connected to the second end of the quantum light source, thereby forming a Sagnac ring. AMZI1 has a first single-photon output port and AMZI2 has a second single-photon output port; The working principle of the bidirectional pumped quantum light source system is as follows: During operation, the frequency is Or the frequency is and The pump light is input to the input of the multimode interference coupler, and then split into two beams of equal power, which are output from the first and second output ports respectively. The two beams propagate in clockwise and counterclockwise directions within the Sagnac ring. Next, the clockwise and counterclockwise beams enter the input ports of AMZI1 and AMZI2 respectively. The phase of AMZI1 and AMZI2 is adjusted by a phase shifter so that the pump light is output from the first output port of AMZI1 and the first output port of AMZI2 with maximum efficiency and enters the quantum light source. Two pump beams excite a quantum light source to produce single photons from clockwise and counterclockwise directions, respectively. Under the nonlinear effect of spontaneous four-wave mixing, the quantum light source produces photons with frequencies of [frequency value missing] in both the clockwise and counterclockwise directions. The signal photons and frequencies are The idler photons, residual pump light, and generated single photons propagate in opposite directions. Clockwise generated single photons and pump light enter AMZI2, while counter-clockwise generated single photons and pump light enter AMZI1. At this point, for both clockwise and counter-clockwise directions, the pump light, signal, and idler photons are all input from the same port to the corresponding AMZI1 and AMZI2. Therefore, AMZI1 and AMZI2, under filtering, separate them to different output ports. Specifically, the implementation is as follows: The pump light will be output from the input terminals of AMZI1 and AMZI2, and then return to the multimode interference coupler. The pump light is always within the Sagnac ring. However, the clockwise and counterclockwise propagating single photons will be output from the second single photon output port and the first single photon output port, respectively, thus separating from the pump light and leaving the Sagnac ring. At this point, the single photon generation and extraction of the bidirectional pumped quantum light source are completed.

2. The bidirectional pumped quantum light source system according to claim 1, characterized in that, The first and second single-photon output ports are connected to the quantum circuit, respectively, so that the single photon can be detected by the detector.

3. The bidirectional pumped 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.

4. The bidirectional pumped quantum light source system according to claim 1, characterized in that, To ensure that pump light and signal / idle photons, when input from the same port to AMZI1 and AMZI2, will output from different ports, the free spectral ranges of AMZI1 and AMZI2 are designed. Assume the frequency difference between the pump light and the target single photon generated by the quantum light source is... Then the free-wave spectrum ranges of AMZI1 and AMZI2 are , where k is a non-negative integer.

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