An optical quantum GKP state generating device and method based on cavity quantum electrodynamics

Abstract

The application belongs to the technical field of quantum computing, and particularly relates to a light quantum GKP state generating device and method based on cavity quantum electrodynamics. The application is based on a high-integration cavity quantum electrodynamics system composed of a nano-beam optical cavity and an equivalent three-energy-level system, so that when the compressed light resonates in the nano-beam optical cavity, the light quantum state is subjected to displacement and controlled rotation operation in cooperation with the equivalent three-energy-level system, and high-quality light quantum GKP states can be generated. The light quantum GKP state generating device for fault-tolerant quantum computing disclosed in the application is beneficial to the development of light quantum information technology towards integration, practicality and large-scale commercialization.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of quantum computing, and particularly relates to a light quantum GKP state generation device and method based on cavity quantum electrodynamics. BACKGROUND

[0002] Quantum error correction is a necessary step for constructing a large-scale quantum computer with real noise components. In 2001, "Encoding a qubit in an oscillator Daniel Gottesman" (Physical Review A, 2001, 64(1): 012310) proposed an error correction protocol, which encodes each quantum bit as a continuous variable Bose mode, called GKP state. Through this encoding, as long as a high-quality GKP encoding state is provided, a small amount of loss error or small displacement error can be corrected using Gaussian operations. GKP error correction is particularly suitable for long-distance quantum communication schemes and optical cluster state related research, and only uses a beam splitter, a homodyne detector and a GKP state preparation device to realize quantum relay.

[0003] However, the required GKP state is a non-Gaussian state, which is difficult to produce in experiments. Therefore, the core of GKP encoding error correction is to solve the problem of how to prepare the GKP state. Until recently, the GKP state has been prepared in the motion mode of the ion trap and the microwave cavity field of the superconducting circuit. However, the GKP state prepared in these experiments is not suitable for preparing a flying GKP state that can be transmitted over a long distance, because only light can be transmitted over a long distance in modern communication networks, so it is very important to explore corresponding measures to prepare a light quantum GKP state. SUMMARY

[0004] In view of the above problems, the application provides a light quantum GKP state generation device and method based on cavity quantum electrodynamics, which aims to solve the influence of real noise on light quantum computing and improve the performance of fault-tolerant algorithms. The application uses cavity quantum electrodynamics (CQED) to perform controlled rotation or displacement operation iteration on the compressed state of light through an equivalent three-level system to generate an optical flying approximate GKP state. The GKP state prepared by the method is probabilistic.

[0005] The technical scheme adopted by the application is as follows:

[0006] An optical quantum GKP state generating device based on cavity quantum electrodynamics, characterized in that it comprises a nanobeam optical cavity 1, an equivalent three-level system 2, a coupling optical fiber 3, a compressed light source 4, a control signal source 5, a first beam splitter 6, a phase modulator 7, a second beam splitter 8, a first detector 9, a second detector 10, and a homodyne detection device 11.

[0007] The compressed light source 4 and the control signal source 5 are respectively connected to the two input ends of the first beam splitter 6; the two output ends of the first beam splitter 6 are respectively connected to the input end of the coupling optical fiber 3 and the input end of the phase modulator 7; the output end of the coupling optical fiber 3 and the output end of the phase modulator 7 are respectively connected to the two input ends of the second beam splitter 8; the two output ends of the second beam splitter 8 are respectively connected to the input end of the first detector 9 and the input end of the second detector 10; the output ends of the first detector 9 and the second detector 10 are respectively connected to the input ends of the homodyne detection device 11.

[0008] The control signal source 5 is used to generate a control signal that changes the ground state spin state of the equivalent three-level system 2 and input into the first beam splitter 6.

[0009] The first beam splitter 6 is used to divide the light output by the compressed light source 4 into two parts, one of which is incident into the coupling optical fiber 3, and the other of which is incident into the phase modulator 7, wherein the compressed light incident into the coupling optical fiber 3 is combined with the signal generated by the control signal source 5.

[0010] The compressed light input into the coupling optical fiber 3 is coupled into the nanobeam optical cavity 1 through the evanescent field, the compressed light in the nanobeam optical cavity 1 interacts with the equivalent three-level system 2, and the compressed light is subjected to displacement and controlled rotation operation, and then coupled back into the coupling optical fiber 3 through the evanescent field, thereby obtaining the GKP state optical signal.

[0011] The phase modulator 7 causes the light to move in phase.

[0012] The second beam splitter 8 is used to combine the light output from the coupling optical fiber 3 and the phase modulator 7, and divide the combined light into two beams, one of which is input to the first detector 9, and the other of which is input to the second detector 10.

[0013] The first detector 9 and the second detector 10 are used to detect the energy of the input light.

[0014] The homodyne detection device 11 is used to detect the output quantum state.

[0015] Further, the nanobeam optical cavity 1 is composed of a reflection region and a resonance region, wherein the reflection region is used to reflect the arriving light to form a reflection optical cavity, and the resonance region is used to retain a fixed optical mode to produce resonance.

[0016] Further, the equivalent three-level system 2 includes two ground states with a frequency interval in the microwave band, corresponding to the upper spin energy level and the lower spin energy level, and an excited state with a frequency interval in the optical band from the ground state, wherein the upper spin or lower spin energy level can be strongly coupled with the resonant mode in the nanobeam optical cavity 1, and the spin state of the ground state is controlled by the control signal.

[0017] Further, the equivalent three-level system 2 is embedded in the middle position of the resonant region of the nanobeam optical cavity 1; the equivalent three-level system 2 is one of an atomic system, a spin system, an ion system or a quantum dot system, and the implementation of embedding the nanobeam optical cavity 1 is ion doping or optical tweezer trapping the equivalent three-level system 2 on the surface of the nanobeam optical cavity 1.

[0018] Further, the coupling distance between the coupling optical fiber 3 and the nanobeam optical cavity 1 is in the range of 100 nm-200 nm, and the typical value is 140 nm.

[0019] Further, the material used by the nanobeam optical cavity 1 is one of silicon (Si), lithium niobate (LiNbO3) and diamond (C), and the typical material is Si, and the substrate layer is silicon dioxide (SiO2).

[0020] Further, the compressed light source 4 is a single-mode compressed light source with a compression degree greater than 10 dB, and the typical value is 10 dB, which is generated by optical parametric amplification, cavity optical force system and the like.

[0021] Further, the first beam splitter 6 and the second beam splitter 8 are 50 / 50 beam splitters.

[0022] Further, the phase modulator 7 is one of an acousto-optic phase modulator, an electro-optic phase modulator and a thermo-optic phase modulator; and the first detector 9 and the second detector 10 are photodiode detectors.

[0023] A method for generating an optical quantum GKP state based on cavity quantum electrodynamics, comprising the following steps: generating compressed-state light by using a compressed light source 4; splitting the output light beam into two parts by a first beam splitter 6, and respectively inputting the two parts into a phase modulator 7 and a coupling optical fiber 3; coupling the compressed-state light into a nanobeam optical cavity 1 through the coupling optical fiber 3 to make the light generate resonance; controlling the ground state spin direction of an equivalent three-level system 2 by a control signal generated by a control signal source 5, and the energy difference between the ground state level and the excited state level of the equivalent three-level system 2 satisfies the resonance coupling condition of the light in the nanobeam optical cavity 1, so that the nanobeam optical cavity 1 cooperates with the equivalent three-level system 2 and the control signal to perform displacement and controlled rotation operations on the compressed optical quantum state, and an optical quantum GKP state is generated; the output light is coupled back into the coupling optical fiber 3 through evanescent field coupling and is output; the phase modulator 7 performs phase modulation on the split compressed light; the modulated light and the resonant light output by the coupling optical fiber 3 are combined and interfered by a second beam splitter 8, the combined light is input into a first detector 9 and a second detector 10 for energy detection, and the electrical signal detected is used to test the Winger function of the phase space by a homodyne detection device 11 and perform quantum state tomography to analyze the corresponding quantum state.

[0024] The method has the advantages that: the compressed-state light is coupled into the nanobeam optical cavity 1 through evanescent field coupling, when the compressed light resonates in the nanobeam optical cavity 1, the displacement and controlled rotation operations are performed on the compressed optical quantum state by cooperating with the equivalent three-level system 2 and the control signal, and a high-quality optical quantum GKP state can be generated, and the output quantum state is tomographically detected by using the homodyne detection method. The method applies the nanometer structure cavity quantum electrodynamics system, sets the parameters of the air hole of the cavity quantum electrodynamics system, adjusts the effective refractive index in the cavity, makes the compressed light resonate in the nanobeam optical cavity 1, and performs displacement and controlled rotation operations on the compressed optical quantum state by cooperating with the equivalent three-level system 2 and the control signal. The method can lay a foundation for exploring quantum measurement and quantum error correction algorithm based on spatial compression state, and has important application value in complex quantum information processing. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a structure schematic diagram of the nanobeam optical cavity of the embodiment of the method;

[0026] Figure 2 It is a structure schematic diagram of the method for generating an optical quantum GKP state based on cavity quantum electrodynamics of the embodiment of the method;

[0027] Figure 3 It is a rotation and displacement operation schematic diagram of the embodiment of the method;

[0028] Figure 4The Winger phase space diagram of the GKP state prepared by a method for generating photonic GKP states based on cavity quantum electrodynamics according to an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram of the iterative system evaluation curve of an embodiment of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments. Example

[0031] like Figure 1 As shown, the structure of this embodiment includes a nanobeam optical cavity 1, an equivalent three-level system 2, a coupled optical fiber 3, a compressed light source 4, a control signal source 5, a first beam splitter 6, a phase modulator 7, a second beam splitter 8, a first detector 9, a second detector 10, and a zero-difference detection device 11.

[0032] The compressed light source 4 and the control signal source 5 are respectively connected to the two input terminals of the first beam splitter 6; the two output terminals of the first beam splitter 6 are respectively connected to the coupling fiber 3 and the phase modulator 7; the output terminals of the coupling fiber 3 and the phase modulator 7 are respectively connected to the two input terminals of the second beam splitter 8; the two output terminals of the second beam splitter 8 are respectively connected to the first detector 9 and the second detector 10; the output terminals of the first detector 9 and the second detector 10 are respectively connected to the input terminals of the zero-difference detection device 11.

[0033] The nanobeam optical cavity 1 consists of a reflective region and a resonant region. In this embodiment, a two-end reflective nanobeam optical cavity is used, comprising a first reflective region, a resonant region, and a second reflective region. This is used in conjunction with the equivalent three-level system 2 and a control signal to perform controlled rotation and displacement operations on the compressed light, thereby generating high-quality photonic quantum GKP states. The integrated device that generates GKP states using an equivalent two-level nanobeam optical cavity system is achieved through the following technical solution, comprising: a bottom-up designed substrate layer and a nanobeam optical cavity;

[0034] The substrate layer is SiO2, and in this embodiment, the thickness of the substrate layer is 725 μm.

[0035] The materials used for the nanobeam optical cavity 1 include, but are not limited to, single-crystal silicon, lithium niobate, diamond, etc. Taking single-crystal silicon as an example, the following description is provided, including the air hole region and the silicon region. In this embodiment, the thickness of the nanobeam optical cavity 1 is 2 μm.

[0036] The nanobeam optical cavity 1 adopts a two-end reflective nanobeam optical cavity structure, including a first reflection region, a resonant region, and a second reflection region. The air hole region is used to change the refractive index of the first reflection region, the resonant region, and the second reflection region in the nanobeam optical cavity 1.

[0037] The resonance region of the nanobeam optical cavity 1 is used to retain a fixed optical mode, generating resonance. The resonance region includes X coupling air holes; the horizontal half-axis length of the coupling air holes increases from the center to both sides, and the spacing between the coupling air holes and the adjacent coupling air holes close to the center direction increases from the center to both sides; the resonance region of the nanobeam optical cavity 1 in this embodiment includes 13 coupling air holes, and the radius of the coupling air holes is 0.28 times the corresponding spacing.

[0038] The first reflection region and the second reflection region in the nanobeam optical cavity 1 are used to reflect the arriving light, forming a two-end reflection optical cavity. The first reflection region and the second reflection region each include Y equally spaced reflection air holes, and Y is a positive integer greater than or equal to 6; in this embodiment, the first reflection region and the second reflection region each include 6 equally spaced reflection air holes, and the vertical half-axis length of the reflection air holes is 180 nm, the horizontal half-axis length is 125 nm, and the spacing is 475 nm.

[0039] The equivalent three-level system 2 includes two ground states with a frequency interval in the microwave frequency band, corresponding to the upper spin energy level and the lower spin energy level, and an excited state with a frequency interval in the optical frequency band from the ground state, wherein the upper spin or lower spin energy level can be strongly coupled with the resonance mode in the nanobeam optical cavity 1. By adjusting the spin state through a microwave control signal and cooperating with the nanobeam optical cavity 1, controlled rotation and displacement operations are performed on the optical quantum state, and a GKP state optical mode is generated. In this embodiment, a rubidium atomic system is used, and the equivalent three-level system is trapped in the middle position of the resonance region of the nanobeam optical cavity 1 by using an optical tweezer, so as to ensure that the coupling energy is at the maximum (the coupling efficiency is the highest);

[0040] The coupling optical fiber 3 is used to couple the compressed light into the resonance region of the nanobeam optical cavity 1 through the evanescent field, and to generate resonance in the resonance region. The resonant light signal is coupled into the coupling optical fiber 3 through the evanescent field, and the optical signal outputs a GKP state optical signal along the coupling optical fiber 3. The shortest distance between the coupling optical fiber 3 and the resonance region of the nanobeam optical cavity 1 is the coupling spacing, and in this embodiment, the thickness of the coupling layer is 220 nm, and the coupling spacing is 140 nm;

[0041] The compressed light source 4 is used to generate light in a squeezed state, which refers to the compression of the phase space. In this embodiment, an optical parametric amplifier is used, in which strong pump light passes through a second-order nonlinear crystal, and one photon in the pump light is split into two lower-energy photons. The frequency, wave vector, and polarization of the generated photons are determined by the phase matching condition. If the two generated photons are degenerate, that is, all degrees of freedom such as frequency, direction, and polarization are indistinguishable, a single-mode squeezed state is generated;

[0042] The resonant light signal of the squeezed state is coupled into the nanobeam optical cavity 1 through an evanescent field, and when the squeezed light is resonant in the nanobeam optical cavity 1, the light quantum state is subjected to displacement and controlled rotation operation in cooperation with the equivalent three-level system 2, thereby generating a high-quality optical quantum GKP state.

[0043] The control signal source 5 is used to generate a control signal for changing the spin of the ground state of the equivalent three-level system, and the frequency of the generated control signal satisfies the coupling condition of the energy difference of the ground state of the two spins in the equivalent three-level system 2.

[0044] The first beam splitter 6 is used to divide the light output by the squeezed light source 4 into two parts, one of which is incident into the coupling optical fiber 3, and the other of which is incident into the phase modulator 7, and the squeezed light source 4 and the control signal source 5 are combined into the nanobeam optical cavity 1, and the beam splitting ratio of the beam splitter is 50 / 50.

[0045] The phase modulator 7 is used to cause the current light path to produce a phase shift, and in the embodiment, a lithium niobate electro-optic phase modulator is used, the working wavelength is C+L waveband, the half-wave voltage is 2.28 V, the waveguide cross-section size is 1 μm*0.5 μm, and the insertion loss is 3.68 dB.

[0046] The second beam splitter 8 is used to combine the light output from the coupling optical fiber 3 and the phase modulator 7, and divide the combined light into two beams, one of which is input into the first detector 9, and the other of which is input into the second detector 10, and the beam splitting ratio of the beam splitter is 50 / 50.

[0047] The first detector 9 and the second detector 10 are used to detect the energy of the input light, and in the embodiment, a light power meter PM100D of Thorlabs Company is used, the detection wavelength range is 800 nm-1700 nm, and the maximum detection power is 20 mW.

[0048] The homodyne detection device 11 is used to subtract the results of the first detector 9 and the second detector 10, and perform optical quantum state tomography, which is operated on a host computer.

[0049] In the above embodiment, the phase modulator 7 is driven by changing the electrical signal to realize phase modulation, and the homodyne detection device 11 is used to scan the interference results at different phases, thereby obtaining the optical quantum state tomography result.

[0050] To solve the above technical problems, the embodiment of the present application provides a kind of based on cavity quantum electrodynamics optical quantum GKP state generation method implementation, comprising the following steps:

[0051] The compressed light is generated by the compressed light source 4, the output light beam is divided into two parts by the first beam splitter 6, and is input into the phase modulator 7 and the coupling optical fiber 3 respectively; the compressed light is coupled into the nanobeam optical cavity 1 through the coupling optical fiber 3, so that the resonance is generated; the ground state spin direction of the equivalent three-level system 2 is regulated by the control signal generated by the control signal source 5, the energy difference between the ground state level and the excited state level of the equivalent three-level system 2 satisfies the resonance coupling condition of the light in the nanobeam optical cavity 1, so that the nanobeam optical cavity 1 cooperates with the equivalent three-level system 2 and the control signal to perform displacement and controlled rotation operation on the compressed light quantum state, and the optical quantum GKP state is generated; the output light is coupled back into the coupling optical fiber 3 through the evanescent field and is output; the phase modulator 7 performs phase modulation on the compressed light after beam splitting; the modulated light and the resonant light output from the coupling optical fiber 3 are combined and interfered by the second beam splitter 8, the combined light is input into the first detector 9 and the second detector 10 for energy detection, the electrical signal detected by the zero difference detection device 11 is used for testing the Winger function of the phase space, the Winger phase space diagram of the prepared optical quantum GKP state is obtained, and the corresponding quantum state is analyzed. In the embodiment, the evaluation value of the optical quantum GKP state preparation system under different iteration numbers is tested respectively, and the system evaluation curve after iteration is obtained.

[0052] Figure 3 The rotation and displacement operation schematic diagram of the embodiment of the application is shown.

[0053] Figure 4 The GKP state Winger phase space diagram prepared by the optical quantum GKP state generation method based on cavity quantum electrodynamics is shown. Figure 4 The horizontal coordinate is the position component of the generated quantum state, and the vertical coordinate is the momentum component of the generated quantum state.

[0054] Figure 5 The system evaluation curve after iteration of the embodiment of the application is shown. Figure 5 The horizontal coordinate is the internal cooperativity of the optical quantum GKP state generation device based on cavity quantum electrodynamics, and the vertical coordinate is the effective compression amount of the generated quantum state.

[0055] The optical quantum GKP state generation system for fault-tolerant quantum computing disclosed in the application can be used in the fields of quantum communication, quantum computing and quantum precision measurement, and is beneficial to the development of optical quantum information technology towards integration, practicality and large-scale commercialization.

Claims

1. An optical quantum GKP state generation device based on cavity quantum electrodynamics, characterized by, The device comprises a nanobeam optical cavity (1), an equivalent three-level system (2), a coupling optical fiber (3), a compressed light source (4), a control signal source (5), a first beam splitter (6), a phase modulator (7), a second beam splitter (8), a first detector (9), a second detector (10), and a homodyne detection device (11). The nanobeam optical cavity (1) is composed of a reflection region and a resonance region, wherein the reflection region is used for reflecting the arriving light to form a reflection optical cavity, and the resonance region is used for retaining a fixed optical mode to produce resonance. The equivalent three-level system (2) comprises two ground states with a microwave frequency interval, corresponding to an upper spin energy level and a lower spin energy level, and an excited state with a light frequency interval from the ground state, wherein the upper spin or lower spin energy level can be strongly coupled with the resonance mode in the nanobeam optical cavity (1), and the spin state of the ground state is controlled by the control signal. The compressed light source (4) and the control signal source (5) are respectively connected to the two input ends of the first beam splitter (6); the two output ends of the first beam splitter (6) are respectively connected to the input end of the coupling optical fiber (3) and the input end of the phase modulator (7); the output end of the coupling optical fiber (3) and the output end of the phase modulator (7) are respectively connected to the two input ends of the second beam splitter (8); the two output ends of the second beam splitter (8) are respectively connected to the input end of the first detector (9) and the input end of the second detector (10); the output ends of the first detector (9) and the second detector (10) are respectively connected to the input ends of the homodyne detection device (11). The control signal source (5) is used to generate a control signal for changing the spin state of the ground state of the equivalent three-level system (2) and inputting the control signal into the first beam splitter (6). The first beam splitter (6) is used to divide the light output by the compressed light source (4) into two parts, one of which is incident into the coupling optical fiber (3), and the other of which is incident into the phase modulator (7), wherein the compressed light incident into the coupling optical fiber (3) is combined with the signal generated by the control signal source (5). The compressed light input into the coupling optical fiber (3) is coupled into the nanobeam optical cavity (1) through evanescent field, the compressed light in the nanobeam optical cavity (1) interacts with the equivalent three-level system (2), and the compressed light is subjected to displacement and controlled rotation operation, and then the compressed light is coupled back into the coupling optical fiber (3) through evanescent field, thereby obtaining a GKP state optical signal. The phase modulator (7) causes the light to produce a phase shift. The second beam splitter (8) is used to combine the light output from the coupling optical fiber (3) and the phase modulator (7), and divide the combined light into two beams, one of which is input into the first detector (9), and the other of which is input into the second detector (10). The first detector (9) and the second detector (10) are used to detect the energy of the input light. The homodyne detection device (11) is used to detect the output quantum state. 2.The optical quantum GKP state generation device based on cavity quantum electrodynamics of claim 1, wherein The equivalent three-level system (2) is embedded in the middle of the resonant region of the nanobeam optical cavity (1); the equivalent three-level system (2) is one of an atomic system, a spin system, an ion system or a quantum dot system, and the nanobeam optical cavity (1) is implemented by ion doping or optical tweezers to confine the equivalent three-level system (2) on the surface of the nanobeam optical cavity (1). 3.The optical quantum GKP state generation device based on cavity quantum electrodynamics of claim 1, wherein The coupling optical fiber (3) and the nanobeam optical cavity (1) have a coupling distance in the range of 100 nm-200 nm. 4.The optical quantum GKP state generation device based on cavity quantum electrodynamics of claim 1, wherein, The nanobeam optical cavity (1) is made of one of silicon (Si), lithium niobate (LiNbO3) and diamond (C). 5.The optical quantum GKP state generation device based on cavity quantum electrodynamics of claim 1, wherein, The compressed light source (4) is a single-mode compressed light source with a compression degree greater than 10 dB. 6.The optical quantum GKP state generation device based on cavity quantum electrodynamics of claim 1, wherein, The first beam splitter (6) and the second beam splitter (8) are 50 / 50 beam splitters. 7.The optical quantum GKP state generation device based on cavity quantum electrodynamics of claim 1, wherein The phase modulator (7) is one of an acousto-optic phase modulator, an electro-optic phase modulator and a thermo-optic phase modulator; and the first detector (9) and the second detector (10) are photodiode detectors.

8. A method for generating an optical quantum GKP state based on cavity quantum electrodynamics, characterized in that, The device for generating a GKP state of a light quantum based on cavity quantum electrodynamics according to any one of claims 1-7 comprises the following steps: a compressed state light is generated by using a compressed light source (4), the output light beam is divided into two parts by a first beam splitter (6), and the two parts are respectively incident on a phase modulator (7) and a coupling optical fiber (3); the compressed state light is coupled into a nanobeam optical cavity (1) by the coupling optical fiber (3) to generate resonance; the ground state spin direction of an equivalent three-level system (2) is regulated by a control signal generated by a control signal source (5), the energy difference between the ground state and the excited state of the equivalent three-level system (2) satisfies the resonance coupling condition of the light in the nanobeam optical cavity (1), so that the nanobeam optical cavity (1) cooperates with the equivalent three-level system (2) and the control signal to displace and control the rotation of the compressed light quantum state, thereby generating a GKP state of a light quantum; the output light is coupled back into the coupling optical fiber (3) by an evanescent field and is output; the phase modulator (7) modulates the phase of the compressed light after beam splitting; the modulated light and the resonant light output by the coupling optical fiber (3) are combined and interfered by a second beam splitter (8), the combined light is input into a first detector (9) and a second detector (10) for energy detection, and the electrical signals detected are used to test the Winger function of the phase space by a homodyne detection device (11) and perform quantum state tomography, thereby analyzing the corresponding quantum state.

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