WO2022246715A1 - 集成光源和控制非门光量子计算芯片及采用其的教学系统 - Google Patents

集成光源和控制非门光量子计算芯片及采用其的教学系统 Download PDF

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WO2022246715A1
WO2022246715A1 PCT/CN2021/096200 CN2021096200W WO2022246715A1 WO 2022246715 A1 WO2022246715 A1 WO 2022246715A1 CN 2021096200 W CN2021096200 W CN 2021096200W WO 2022246715 A1 WO2022246715 A1 WO 2022246715A1
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gate
control
light source
quantum computing
photons
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French (fr)
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陆朝阳
王辉
王云飞
何玉明
潘建伟
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中国科学技术大学
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06E—OPTICAL COMPUTING DEVICES; COMPUTING DEVICES USING OTHER RADIATIONS WITH SIMILAR PROPERTIES
    • G06E3/00—Devices not provided for in group G06E1/00, e.g. for processing analogue or hybrid data
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09B—EDUCATIONAL OR DEMONSTRATION APPLIANCES; APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE; MODELS; PLANETARIA; GLOBES; MAPS; DIAGRAMS
    • G09B23/00—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes
    • G09B23/06—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for physics
    • G09B23/22—Models for scientific, medical, or mathematical purposes, e.g. full-sized devices for demonstration purposes for physics for optics

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  • the disclosure relates to the field of quantum computing and quantum optics technology, and relates to the design of various optical quantum computing control NOT gate chips, in particular to an optical quantum computing chip with integrated light source and control NOT gate (CNOT) and a teaching system using it, which is suitable for optical quantum computing , teaching experiments and other application fields.
  • CNOT integrated light source and control NOT gate
  • Photons have the advantages of fast operation speed, simple and precise single-bit manipulation, and strong anti-noise ability, and can provide a quantum interface between remote atoms and solid-state quantum systems.
  • the realization of large-scale optical quantum computing and simulation will solve some computing problems that classical computers are not capable of, and will have a profound impact on human society.
  • many large high-tech companies have strongly intervened in quantum computing, which has greatly promoted the development of this field. Therefore, the cultivation of talents in this direction also needs to be trained as early as possible at the university level.
  • universities due to the integration of many disciplines, expensive research equipment, and shortage of technical personnel, universities currently lack professional equipment for quantum computing experiments. Therefore, it is very necessary and urgent to design some quantum computing teaching systems.
  • Optical quantum logic gates have already been realized under various schemes. For example, non-deterministic control phase gates can be realized by relying on fully linear optical devices, single photon sources and photon detectors, and the success rate can be improved through quantum teleportation. , but consumes a lot of device resources and requires very high device precision;
  • the present disclosure provides an optical quantum computing chip integrating a light source and a control NOT gate and a teaching system using the same, in order to at least partly solve the above technical problems.
  • an optical quantum computing chip integrating a light source and a control NOT gate
  • the chip includes a coherent excitation light source, a single-bit gate, a control NOT gate circuit and a detection module;
  • the coherent excitation light source emits two photons, prepares any single-bit state photons through the two single-bit gates, and inputs them into the control NOT gate circuit, and is detected by the detection module after passing through the control NOT gate circuit .
  • the chip integrates the coherent excitation light source, the single-bit gate and the control NOT gate circuit, or integrates the coherent excitation light source, the single-bit gate, the control NOT gate circuit and the detection module on the semiconductor chip.
  • the coherent excitation light source adopts a silicon waveguide structure, a silicon nitride microcavity structure or a periodically poled lithium niobate waveguide structure.
  • the periodically polarized lithium niobate material absorbs two photons with a frequency of , and emits signal light and idler light with a frequency of and respectively; two light sources are used to generate 2 pairs of photons, and one photon in each pair of photons will directly Send it into the detection module as a single photon forecast; and two photons with the same frequency will be sent into the circuit to realize the operation of the control NOT gate.
  • the single-bit gate and the control NOT gate circuit jointly form an optical quantum logic gate.
  • control NOT gate circuit includes a beam splitter and a phase shifter, and the splitting ratio of the beam splitter and the phase of the phase shifter need to be adjusted arbitrarily, so as to realize unitary transformation.
  • the change of the displacement of the phase shifter is realized by locally changing the temperature of the phase shifter in the waveguide to control the refractive index of the waveguide; the beam splitting ratio of the beam splitter is changed by a Mach-Zehnder interferometer.
  • the detection module includes an integrated superconducting nanowire single photon detector or a photon number detector connected to an optical fiber outside the chip through a grating coupler.
  • a teaching system which includes the optical quantum computing chip as described above.
  • the teaching system also includes a teaching control system, and the teaching control system is used to control the phase shift of the phase shifter in the control NOT gate circuit.
  • FIG. 1 is a schematic diagram illustrating the coupling of a coherent excitation light source, a control NOT gate circuit, a single photon detection module and a control system according to an embodiment of the present disclosure
  • FIG. 2 illustrates the principle of the four-wave mixing process and a schematic diagram of a silicon-based predictive single photon source according to an embodiment of the present disclosure
  • Fig. 3 illustrates a single-photon bit gate of path encoding and a schematic diagram of a single-bit gate implemented by a beam splitter and a phase shifter according to an embodiment of the present disclosure
  • FIG. 4 illustrates a schematic circuit diagram of a Mach-Zehnder interferometer according to an embodiment of the present disclosure
  • FIG. 5 illustrates a schematic diagram of a control NOT gate and a circuit diagram of a control NOT gate according to an embodiment of the present disclosure
  • FIG. 6 illustrates a schematic diagram of an integrated superconducting nanowire single photon detector and an external single photon detector according to an embodiment of the present disclosure
  • FIG. 7 illustrates a teaching system for controlling a NOT gate chip based on a silicon waveguide forecasting single photon source according to an embodiment of the present disclosure
  • FIG. 8 illustrates a teaching system for controlling a NOT gate chip based on a silicon nitride microcavity forecasting single photon source according to an embodiment of the present disclosure
  • Figure 9 illustrates the spontaneous parametric down-conversion process and the schematic diagram of the periodically poled lithium niobate waveguide
  • FIG. 10 schematically illustrates a teaching system for controlling a NOT gate chip based on a periodically polarized lithium niobate waveguide predicting a single photon source according to an embodiment of the present disclosure.
  • the schematic diagram of the overall structure of the control NOT gate chip teaching system designed in this design is shown in Figure 1.
  • the coherent excitation light source emits two photons prepared to the path code
  • the single photon detection module After passing through the control NOT gate, the single photon detection module detects, and the phase shift of the phase shifter in the control NOT gate circuit can be controlled by the control system.
  • the light source part can be realized through four-wave mixing or parametric down-conversion process shown in FIG. 2 .
  • Universal quantum logic gates can be realized by arbitrary single-bit gates and controlled NOT gates (C-NOTs). As shown in Figure 3, the photon bits are coded on two paths.
  • the splitting ratio of the beam splitter and the phase of the phase shifter can be adjusted arbitrarily.
  • the phase change is achieved by controlling the refractive index of the waveguide by locally changing the temperature of the phase shifter in the waveguide.
  • the splitting ratio of the beam splitter is changed by a Mach Zehnder Interferometer (MZI).
  • the interferometer includes two 50:50 beam splitters, one of the interference arms is equipped with Au/Ti heating electrodes, after the current is passed, the phase between the two paths of the interferometer will change, so that Change the light intensity of the output port to achieve the purpose of adjustable beam splitting ratio.
  • the phase shifter is equivalent to the Rz single-bit gate
  • the Mach-Zehnder interferometer is equivalent to the Ry single-bit gate, so the structure in Figure 3(ii) can realize any single-bit gate operation on a single photon bit.
  • Figure 5(i) is the integrated optical path connection for realizing the controlled NOT gate (CNOT), and Figure 5(ii) is the schematic diagram of the optical path for realizing the controlled NOT gate, in which the reflective splitting ratio of the three beam splitters is 1/3, and the two The reflective splitting ratio of each beam splitter is 1/2.
  • a Mach-Zehnder interferometer is also used to realize the beam splitter with adjustable beam splitting ratio. The actual optical path is shown in Fig. 5(iii).
  • the control of the input state of the CNOT line can be realized through single-bit unitary transformation.
  • the two outputs of CNOT line c and t can be detected by an integrated superconducting nanowire single photon detector, or can be connected to an off-chip photon number detector through a grating coupler.
  • the CNOT operation is successful, and the success probability is 1/9.
  • the detector is connected with an electronic control device, which can display whether the CNOT operation is successful and perform subsequent output and counting.
  • the present disclosure provides silicon-based, Si3N4 and laser direct writing lithium niobate integrated CNOT chips based on traditional CMOS technology.
  • the chip integrates the light source and circuit part, or integrates all the light source, circuit and detection part on the semiconductor chip.
  • the light source part can be realized by various materials.
  • This patent provides the use of Si or Si3N4 microcavities or waveguides to provide single photons through the process of four-wave mixing. As shown in Fig. 2(i), the material absorbs two photons with frequency ⁇ 0 and emits signal light and idler light with frequencies ⁇ 1 and ⁇ 2 , respectively. Since two light sources are used, the light source can generate 2 pairs of photons.
  • Figure 2(ii) shows part of the waveguide-based light source.
  • the input and output of the light source are coupled by a grating.
  • This light source design is suitable for silicon-based waveguides.
  • a better design is a four-wave mixing light source based on a silicon or silicon nitride microring cavity. This design can naturally achieve phase matching conditions, and the photon coherence length can reach millimeter or even centimeter level.
  • the pump light input is coupled into the two-mode waveguide by a 50:50 beam splitter, and the purity of the outgoing photon can be improved by adding an appropriate phase delay to the low-order mode; the ring structure is to save space and increase the purity of the outgoing photon and conversion efficiency, and the outgoing photons are directly coupled into the waveguide.
  • a source that coherently excites multiple such structures can preserve high photon indistinguishability.
  • the redundant excitation light is exported to the chip by the directional coupler and the waveguide to avoid affecting the stability of the whole chip.
  • the efficiency itself is extremely high.
  • one of our methods is to couple the generated photons into a single-mode fiber (or multi-mode fiber) through a waveguide, and the prediction efficiency can be as high as 80%.
  • Another method is to directly grow superconducting nanowire single photon detectors on the chip. The entire chip operates at a temperature of ⁇ 2K, and the predicted efficiency can reach more than 95%.
  • Periodically poled lithium niobate materials can undergo quasi-phase-matched second-order spontaneous parametric down-conversion nonlinear processes. Since the second-order nonlinear coefficients are usually much higher than the third-order nonlinear coefficients, this process is more complex than the third-order spontaneous four-wave mixing. The frequency process is more likely to occur, and the compressed vacuum state of materials such as silicon base and silicon nitride can be obtained under the same pump laser power. Through the second-order spontaneous parametric down-conversion process, the periodically poled lithium niobate waveguide can be fabricated into a single-photon source with high predictive efficiency, high purity, and high inresolution. As shown in Fig.
  • Lithium niobate is a ferroelectric crystal, and the orientation of the electric dipole moment of each unit cell depends on the position of niobium and lithium ions in the unit.
  • the crystal structure can be reversed by a strong electric field, so that periodically arranged poled lithium niobate crystals can be made.
  • the periodic lithium niobate waveguide is shown in Fig. 9(ii).
  • This design achieves a high-efficiency predictive single-photon source through spontaneous parametric down-conversion in a periodically poled lithium niobate waveguide.
  • the integrated quantum circuit based on the periodic lithium niobate waveguide prediction single photon source is shown in Figure 10.
  • Embodiment 1 of the present disclosure a silicon light source-based teaching system for an integrated miniaturized optical quantum control NOT gate chip is provided. , single photon detector module and teaching control system, which can be applied to the demonstration teaching of optical quantum control NOT gate, the teaching demonstration of Bell state preparation and inspection.
  • FIG. 1 it includes two predictive single-photon sources for coherent excitation, two single-bit gate circuits for preparing CNOT gate inputs, CNOT gate circuits and a single-photon detection and control system.
  • the pumping pulsed laser passes through the beam splitter and coherently excites two silicon waveguide prediction single photon sources, and the signal is generated through the third-order nonlinear four-wave mixing process in the silicon waveguide
  • Light and idler photon pairs are input and forecast photons as CNOT lines. Redundant background excitation light is guided out of the chip by a waveguide to avoid noise effects.
  • Figure 2(i) shows the four-wave mixing process
  • Figure 2(ii) shows the silicon waveguide predicting the single photon source.
  • the photon state output by the light source is the
  • a single-bit control gate needs to be inserted between the light source and the CNOT input port, as shown in Figure 3(i) . It can be shown that the phase shifter can impose an Rz rotation operation on the single photon path encoded bits,
  • U p represents the unitary transformation of the photon bit by the phase shifter
  • ⁇ 1 represents the phase shift of the upper path of the photon relative to the lower path by the phase shifter
  • R z (- ⁇ 1 ) is the qubit rotation operator, so that the qubit Rotate - ⁇ 1 degree around the Z axis on the Bloch sphere.
  • the Mach-Zehnder interferometer can apply a Ry rotation operation to the single-photon path encoded bits
  • U m represents the unitary transformation of the photon bit by the Mach-Zehnder interferometer
  • ⁇ 2 represents the phase shift of the upper path of the photon relative to the lower path by the phase shifter in the Mach-Zehnder interferometer
  • R y ( ⁇ 2 ) is the qubit The rotation operator makes the qubit rotate ⁇ 2 degrees around the Y axis on the Bloch sphere.
  • the photon path encoding bits can be prepared to any state via the circuit shown in Fig. 3(ii).
  • the Mach-Zehnder interferometer is shown in Figure 4.
  • control NOT gate is composed of three splitters with a splitting ratio of 1/3 and two splitters with a splitting ratio of 1/2, when the control bit (control When the bit) output port c and the target bit output port receive a photon signal at the same time, the control NOT gate operation is successful, and the counting control system records the count; otherwise, the control NOT gate operation fails and the count is discarded.
  • the single-photon detector can be composed of a superconducting nanowire single-photon detector directly integrated into the chip, or it can be coupled into an optical fiber through a grating coupler and connected to an off-chip single-photon detector for detection.
  • Fig. 6(i) is a schematic diagram of a superconducting nanowire single-photon detector
  • Fig. 6(ii) is a schematic diagram of an off-chip single-photon detector.
  • the coherent excitation light source, the CNOT operation circuit, and the single photon detector are connected as shown in the figure. Adjust and control the splitting ratio of each beam splitter in the NOT gate line, and change the input state of the CNOT gate line by changing the phase shift of each phase shifter in the single-bit gate line, observe the count of the output port, and carry out the demonstration operation teaching experiment of the CNOT gate.
  • the light source part uses a silicon nitride microcavity structure, and a four-wave mixing process occurs in the microcavity to generate signal photons and idler photon pairs, which are used as CNOT gate input and forecast photons.
  • the silicon nitride microcavity light source for coherent excitation, the CNOT gate circuit and the single photon detection module are connected as shown in the figure. Adjust and control the splitting ratio of each beam splitter in the NOT gate circuit, and change the input state of the CNOT gate circuit by changing the phase shift of each phase shifter in the single-bit gate circuit, observe the photon count at the output port, and carry out the demonstration teaching experiment of the CNOT gate circuit.
  • the detectors can also be classified into on-chip integrated type or externally connected type.
  • the light source part uses a periodically poled lithium niobate waveguide structure.
  • the periodically poled lithium niobate waveguide In the periodically poled lithium niobate waveguide, quasi-phase-matched second-order nonlinear spontaneous parameters will occur.
  • the conversion process as shown in Fig. 9(i), the photon with frequency ⁇ 0 is transformed into signal light and idler light of ⁇ 1 and ⁇ 2 through the spontaneous parametric down-conversion process, which are used as the input photon and forecast photon of the CNOT gate circuit.
  • Lithium niobate is a ferroelectric crystal, and the orientation of the electric dipole moment of each unit cell depends on the position of niobium and lithium ions in the unit. The crystal structure can be reversed by a strong electric field, so that periodically arranged poled lithium niobate crystals can be made.
  • the periodic lithium niobate waveguide is shown in Fig. 9(ii).
  • the coherently excited periodically polarized lithium niobate waveguide forecast light source, the CNOT gate circuit and the single photon detection module are connected as shown in FIG. 10 .
  • FIG. 2 only show an equivalent single-bit quantum logic gate circuit, and the number and connection mode of the Mach-Zehnder interferometer and phase shifter are not limited to this embodiment, that is, the preparation of the input state of the CNOT gate circuit Single-bit gates are not limited to this embodiment.
  • the multi-mode optical quantum logic gate circuit of the present disclosure has the feature of full connectivity of all modes, that is, it can realize interference among all modes.
  • the optical quantum computing chip with integrated light source and control NOT gate and the teaching system using it have at least one of the following beneficial effects:
  • the present disclosure can avoid complex four-wave mixing frequency degeneracy through on-chip integration of light sources and control NOT gates.
  • the on-chip integration approach has the advantages of high integration, stable working conditions, and low cost.
  • this optical quantum chip can achieve lower optical loss
  • each light-receiving coupler can have close to the same coupling collection efficiency
  • the output of the CNOT gate is connected to the photon number detector, combined with the input end to connect the light source and the single-bit gate, the demonstration operation experiment of the CNOT gate and the entanglement state preparation and inspection experiment can be realized;
  • the photon number non-destructive detector is connected through the CNOT gate output terminal, and can be connected according to specific needs to realize the programmable universal quantum computing chip;
  • the operation of the CNOT gate can be canceled by adjusting the reflective splitting ratio of the beam splitter to 1, which increases the programmability of the chip after etching.

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Abstract

一种集成光源和控制非门（CNOT）的光量子计算芯片，芯片包括相干激发光源、单比特门、控制非门（CNOT）线路和探测模块；其中，相干激发光源发射两个光子，通过两个单比特门制备任意单比特态光子，输入到控制非门（CNOT）线路中，经过控制非门（CNOT）线路后由探测模块进行探测。通过片上集成光源和控制非门（CNOT）可以避免进行复杂的四波混频频率简并，同时，片上集成的途径具有集成度高，工作条件稳定，低成本等优势。

Description

集成光源和控制非门光量子计算芯片及采用其的教学系统 技术领域
本公开涉及量子计算与量子光学技术领域，涉及多种光量子计算控制非门芯片设计，特别涉及一种集成光源和控制非门(CNOT)的光量子计算芯片及采用其的教学系统，适用于光量子计算、教学实验等应用领域。
背景技术
光子具有操作速度快、单比特操纵简单精确、抗噪声能力强等优势，并可为远程的原子和固态量子系统之间提供量子接口。大型光量子计算和模拟的实现，将解决若干经典计算机无法胜任的计算问题，对人类社会产生深刻影响。近年来，许多大型高科技公司强势介入量子计算，对该领域的发展起到极大的促进作用。因此，对该方向的人才培养也需要在大学阶段尽早训练。但由于该方向融合了众多学科，研究设备昂贵，技术人员短缺等原因，目前各个高校对量子计算方面的实验缺少专业的设备。因此，设计若干量子计算教学系统是非常必要且急需研制的。
在实现本公开构思的过程中，发明人发现相关技术中至少存在如下问题：
(1)光学量子逻辑门早已在多种方案下获得实现，如依靠全线性光学器件、单光子源和光子探测器可以实现非确定性的控制相位门，并可以通过量子隐形传态提高成功率，但需要消耗大量器件资源并且需要非常高的器件精度；
(2)基于四波混频的光源要做到频率简并非常复杂，要实现四波混频频率简并，必须通过两个波长不同的激光同时激发非线性材料，同时满足相位匹配条件。这一方面会增加成本，另一方面技术难度较大，且存在布拉格散射、单边激发等问题，降低光子全同性。
因此，亟需一种降低器件资源消耗并可以解决四波混频的光源需要进行频率简并的问题的光量子计算芯片。
发明内容
针对上述技术问题，本公开提供了一种集成光源和控制非门的光量子计算芯片及采用其的教学系统，以期至少部分地解决上述技术问题。
为了实现上述目的，作为本公开的一方面，提供了一种集成光源和控制非门的光量子计算芯片，所述芯片包括相干激发光源、单比特门、控制非门线路和探测模块；其中，
所述相干激发光源发射两个光子，通过两个所述单比特门制备任意单比特态光子，输入到所述控制非门线路中，经过所述控制非门线路后由所述探测模块进行探测。
其中，所述芯片将相干激发光源、单比特门和控制非门线路部分进行集成，或将相干激发光源、单比特门、控制非门线路和探测模块全部集成在半导体芯片上。
其中，所述相干激发光源采用硅波导结构、氮化硅微腔结构或周期性极化铌酸锂波导结构。
其中，周期性极化铌酸锂材料吸收两个频率为的光子，发射频率分别为和的信号光和闲频光；采用两个光源进而产生2对光子，每对光子中的一个光子会直接送入探测模块，作为预报单光子；而频率相同的两个光子会被送入线路实现控制非门的操作。
其中，所述单比特门和所述控制非门线路共同形成光量子逻辑门。
其中，所述控制非门线路包括分束器和移相器，分束器的分束比和移相器的相位需要任意可调，以用于实现么正变换。
其中，所述移相器的位移的改变是通过局部改变波导中的移相器温度控制波导折射率来实现的；所述分束器的分束比是通过马赫曾德干涉仪来改变的。
其中，所述探测模块包括集成的超导纳米线单光子探测器或通过光栅耦合器连接光纤到片外的光子数探测器。
作为本公开的另一方面，提供了一种教学系统，其中，包括如上所述的光量子计算芯片。
其中，所述教学系统还包括教学控制系统，所述教学控制系统用于 控制所述控制非门线路中移相器的相移。
附图说明
图1示意了根据本公开实施例的相干激发光源、控制非门线路、单光子探测模块和控制系统耦合示意图；
图2示意了四波混频过程原理和根据本公开实施例的基于硅的预报单光子源示意图；
图3示意了路径编码的单光子比特门和根据本公开实施例的通过分束器和移相器实现的单比特门线路示意图；
图4示意了根据本公开实施例的马赫曾德干涉仪线路示意图；
图5示意了控制非门原理图和根据本公开实施例的控制非门线路示意图；
图6示意了根据本公开实施例的集成超导纳米线单光子探测器和外接单光子探测器示意图；
图7示意了根据本公开实施例的基于硅波导预报单光子源的控制非门芯片教学系统；
图8示意了根据本公开实施例的基于氮化硅微腔预报单光子源的控制非门芯片教学系统；
图9示意了自发参量下转换过程和周期性极化铌酸锂波导示意图；
图10示意了根据本公开实施例的基于周期性极化铌酸锂波导预报单光子源的控制非门芯片教学系统。
具体实施方式
为使本公开的目的、技术方案和优点更加清楚明白，以下结合具体实施例，并参照附图，对本公开作进一步的详细说明。
本设计的控制非门芯片教学系统整体结构示意图如图1所示，相干激发光源发射两个制备到路径编码|0>的光子，通过两个单比特门可以制备控制非门输入端口的任意单比特态输入。经过控制非门后由单光子探测模块进行探测，控制非门线路中移相器的相移可以通过控制系统控制。其中光源部分可通过图2所示的四波混频或者参量下转换过程实现。
通过任意单比特门和控制非门(C-NOT)可以实现普适量子逻辑门。如图3，光子比特编码在两路径上，为实现任意幺正变换需要分束器的分束比和移相器的相位可以任意调节。通过局部改变波导中的移相器温度控制波导折射率，从而实现相位的改变。分束器的分束比则是通过一个马赫曾德干涉仪(Mach Zehnder Interferometer,MZI)来改变。如图4所示，干涉仪包括两个50:50分束器，其中一条干涉臂上加有Au/Ti的加热电极，在通过电流后，干涉仪两条路径之间的相位会改变，从而改变输出口的出光强度，达到分束比可调的目的。忽略全局相位，移相器相当于Rz单比特门，马赫曾德干涉仪相当于Ry单比特门，因此图3(ii)的结构可以实现对单个光子比特的任意单比特门操作。
图5(i)为实现控制非门(CNOT)的集成光路连接，图5(ii)为实现控制非门的光路原理图，其中三个分束器的反射分束比为1/3，两个分束器的反射分束比为1/2。为了实现光路的可编程和准确调控，同样使用马赫曾德干涉仪来实现分束比可调的分束器，实际光路如图5(iii)所示。
通过单比特幺正变换可以实现对于CNOT线路输入态的控制。CNOT线路c、t两路输出可以通过集成的超导纳米线单光子探测器探测，也可以通过光栅耦合器连接光纤到片外的光子数探测器。当CNOT线路c路输出和t路输出各探测到一个光子时CNOT操作成功，成功概率为1/9，探测器外接电子控制器件，可以显示CNOT操作是否成功并且进行后续的输出和计数。
本公开提供了基于传统CMOS工艺的硅基、Si3N4以及激光直写的铌酸锂集成CNOT芯片。该芯片将光源、线路部分进行集成，或将光源、线路和探测部分全部集成在半导体芯片上。其中光源部分可以通过多种材料实现。本专利提供了利用Si或Si3N4的微腔或波导中通过四波混频的过程提供单光子。如图2(i)所示，材料吸收两个频率为ω 0的光子，发射频率分别为ω 1和ω 2的信号光和闲频光。由于采用了两个光源，因此光源可以产生2对光子。实验时，每对光子中的一个光子会直接送入探测器，当做预报单光子；而频率相同的两个光子会被送入线路实现CNOT 操作。这种设计的好处在于不用产生频率简并的光子对，极大的降低了对光源的要求。
图2(ii)所示为基于波导的光源部分，光源的输入输出由光栅耦合，此光源设计适合基于硅的波导。然而，一种更好的设计是基于硅或者氮化硅微环腔的四波混频光源。该设计可以天然的达到相位匹配条件，且光子相干长度可达毫米甚至厘米级别。泵浦光输入由50:50的分束器耦合到两个模式的波导中，通过在低阶模式一路加适当的相位延迟可以提高出射光子纯度；环形结构是为了节省空间，同时增加出射光子纯度和转换效率，并且出射光子会直接耦合到波导中。相干激发多个这样的结构的光源可以保持很高的光子不可分辨性。冗余的激发光由方向耦合器和波导导出芯片，避免影响整个芯片的稳定性。
由于产生的下转换光子直接耦合到波导中，自身的效率极高。为了得到高的预报效率，我们一种方法是将产生的光子通过波导耦合到单模光纤(或多模光纤)中，预报效率可高达80％以上。另一种方法是直接在芯片上生长超导纳米线单光子探测器，整个芯片在～2k温度下运行，预计预报效率能达到95％以上。
周期性极化铌酸锂材料可以发生准相位匹配的二阶自发参量下转换非线性过程，由于二阶非线性系数通常比三阶非线性系数高很多，此过程比三阶的自发四波混频过程更容易发生，相同泵浦激光功率下可以得到压缩系数远远高于硅基、氮化硅等材料的压缩真空态。通过二阶自发参量下转换过程，周期性极化铌酸锂波导可以制成高预报效率、高纯度、高不可分辨性的单光子源。如图9(i)，频率为ω 0的光子通过自发参量下转换过程转化为ω 1和ω 2的信号光和闲频光。铌酸锂是铁电晶体，每一个晶胞单元的电偶极矩取向取决于该单元中铌和锂离子的位置。通过强电场可以反转晶体结构，从而可以制成周期性排列的极化铌酸锂晶体。如图9(ii)所示周期性铌酸锂波导。
本设计通过周期性极化铌酸锂波导的自发参量下转换实现高效率的预报单光子源。基于周期性铌酸锂波导预报单光子源的集成量子线路如图10所示。
实施例1
在本公开的实施例1中，提供了一种基于硅光源的集成小型化光量子控制非门芯片教学系统，该集成光量子控制非门芯片集成了相干激发的预报单光子源、集成控制非门线路、单光子探测器模块和教学控制系统，可应用于光量子控制非门演示教学，Bell态制备和检验教学演示。
在本实施例中，如图1所示，包括两个相干激发的预报单光子源，两个用于制备CNOT门输入的单比特门线路，CNOT门线路和单光子探测和控制系统。
在本实施例中，如图2所示，泵浦脉冲激光通过分束器分束相干激发两个硅波导预报单光子源，通过硅波导中三阶非线性的四波混频过程，产生信号光和闲频光子对作为CNOT线路输入和预报光子。冗余的背景激发光会由波导导出芯片以避免引起噪声影响。图2(i)为四波混频过程，图2(ii)为硅波导预报单光子源。
在本实施例中，光源输出的光子态为|0>态，为实现任意比特的CNOT门端口输入，需要在光源和CNOT输入端口之间接入单比特控制门，如图3(i)所示。可以证明，移相器可以对单光子路径编码比特施加一个Rz旋转操作，
Figure PCTCN2021096200-appb-000001
其中，U p表示移相器对光子比特的幺正变换，θ 1表示移相器使光子上面一路相对下面一路的相移，R z(-θ 1)是量子比特旋转算符，使量子比特在Bloch球面上绕Z轴旋转-θ 1度。
马赫曾德干涉仪可以对单光子路径编码比特施加一个Ry旋转操作，
Figure PCTCN2021096200-appb-000002
其中，U m表示马赫曾德干涉仪对光子比特的幺正变换，θ 2表示马赫曾德干涉仪中移相器使光子上面一路相对下面一路的相移，R y(θ 2)是量子比特旋转算符，使量子比特在Bloch球面上绕Y轴旋转θ 2度。
经图3(ii)所示线路可以将光子路径编码比特制备到任意的态上。马赫曾德干涉仪如图4所示。
在本实施例中，如图5所示，控制非门(CNOT门)由三个分束比为1/3和两个分束比为1/2的分束器组成，当控制比特(control bit)输出端口c和目标比特(target bit)输出端口同时各接收到一个光子信号时，控制非门操作成功，计数控制系统记录此次计数，否则控制非门操作失败，丢弃此次计数。
在本实施例中，单光子探测器可以由直接集成到片上的超导纳米线单光子探测器组成，也可以通过光栅耦合器耦合到光纤中，连接到片外的单光子探测器中进行探测。图6(i)为超导纳米线单光子探测器示意图，图6(ii)为外接片外单光子探测器示意图。
在本实施例中，如图7所示，相干激发光源、CNOT操作线路，单光子探测器如图示方式连接。调节控制非门线路中各分束器的分束比，并通过改变单比特门线路各移相器相移改变CNOT门线路输入态，观察输出端口的计数，进行CNOT门演示性操作教学实验。
实施例2
在本实施例中，光源部分与实施例1相比改用氮化硅微腔结构，在微腔中发生四波混频过程产生信号光子和闲频光子对，作为CNOT门输入和预报光子。如图8所示，相干激发的氮化硅微腔光源、CNOT门线路和单光子探测模块按如图方式连接。调节控制非门线路中各分束器的分束比，并通过改变单比特门线路各移相器相移改变CNOT门线路输入态，观察输出端口光子计数，进行CNOT门线路演示性教学实验。本实施案例中，探测器也可分为片上集成型或者外接型两种。
实施例3
在本实施例中，光源部分与实施例1相比改用周期性极化铌酸锂波导结构，在周期性极化铌酸锂波导中会发生准相位匹配的二阶非线性的自发参量下转换过程，如图9(i)所示，频率为ω 0的光子通过自发参量下转换过程转化为ω 1和ω 2的信号光和闲频光，作为CNOT门线路的输入光子和预报光子。铌酸锂是铁电晶体，每一个晶胞单元电偶极矩取向取决于该单元中铌和锂离子的位置。通过强电场可以反转晶体结构，从而可以制成周期性排列的极化铌酸锂晶体。如图9(ii)所示周期性铌酸锂波导。
在本实施例中，按照图10方式连接相干激发的周期性极化铌酸锂波导预报光源、CNOT门线路和单光子探测模块。调节控制非门线路中个分束器的分束比，并通过改变单比特门线路各移相器相移改变CNOT门线路输入态，观察输出端口光子计数，进行CNOT门线路演示性教学实验。
需要说明的是，实施例和图2仅仅展示一种等效单比特量子逻辑门线路，马赫曾德干涉仪和移相器数目及连接方式不限于本实施例，即制备CNOT门线路输入态的单比特门线路不限于本实施例。
对所公开的实施例，本公开的多模式光量子逻辑门线路具有所有模式全连通的特点，即能实现所有模式间的干涉。
综上所述，与现有技术相比，本公开的集成光源和控制非门的光量子计算芯片及采用其的教学系统至少具有如下有益效果之一：
(1)本公开通过片上集成光源和控制非门可以避免进行复杂的四波混频频率简并，同时，片上集成的途径具有集成度高，工作条件稳定，低成本等优势。
(2)通过片上集成光源、低损耗集成光学元件和光学镀膜的方法，这种光量子芯片可以达到较低光学损耗；
(3)满足从输入模式准直器到收光耦合器具有相等的光程，即每个收光耦合器能够具有接近相同的耦合收集效率；
(4)CNOT门输出连接光子数探测器，结合输入端连接光源和单比特门，可以实现CNOT门演示性操作实验和纠缠态制备和检验实验；
(5)具有任意可编程的单比特门和CNOT门，通过CNOT门输出端连接光子数非破坏性探测器，可以根据特定需要连接实现可编程普适量子计算芯片；
(6)CNOT门操作可以通过调节分束器反射分束比为1取消，增加了刻蚀后芯片的可编程性。
以上所述的具体实施例，对本公开的目的、技术方案和有益效果进行了进一步详细说明，应理解的是，以上所述仅为本公开的具体实施例而已，并不用于限制本公开，凡在本公开的精神和原则之内，所做的任 何修改、等同替换、改进等，均应包含在本公开的保护范围之内。

Claims (10)

  1. 一种集成光源和控制非门的光量子计算芯片，所述芯片包括相干激发光源、单比特门、控制非门线路和探测模块；其中，
    所述相干激发光源发射两个光子，通过两个所述单比特门制备任意单比特态光子，输入到所述控制非门线路中，经过所述控制非门线路后由所述探测模块进行探测。
  2. 根据权利要求1所述的光量子计算芯片，所述芯片将相干激发光源、单比特门和控制非门线路部分进行集成，或将相干激发光源、单比特门、控制非门线路和探测模块全部集成在半导体芯片上。
  3. 根据权利要求1所述的光量子计算芯片，所述相干激发光源采用硅波导结构、氮化硅微腔结构或周期性极化铌酸锂波导结构。
  4. 根据权利要求3所述的光量子计算芯片，周期性极化铌酸锂材料吸收两个频率为ω 0的光子，发射频率分别为ω 1和ω 2的信号光和闲频光；采用两个光源进而产生2对光子，每对光子中的一个光子会直接送入探测模块，作为预报单光子；而频率相同的两个光子会被送入线路实现控制非门的操作。
  5. 根据权利要求1所述的光量子计算芯片，所述单比特门和所述控制非门线路共同形成光量子逻辑门。
  6. 根据权利要求1所述的光量子计算芯片，所述控制非门线路包括分束器和移相器，分束器的分束比和移相器的相位需要任意可调，以用于实现么正变换。
  7. 根据权利要求6所述的光量子计算芯片，所述移相器的位移的改变是通过局部改变波导中的移相器温度控制波导折射率来实现的；所述分束器的分束比是通过马赫曾德干涉仪来改变的。
  8. 根据权利要求1所述的光量子计算芯片，所述探测模块包括集成的超导纳米线单光子探测器或通过光栅耦合器连接光纤到片外的光子数探测器。
  9. 一种教学系统，包括如权利要求1-8任一项所述的光量子计算芯片。
  10. 根据权利要求9所述的教学系统，所述教学系统还包括教学控制系统，所述教学控制系统用于控制所述控制非门线路中移相器的相移。
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