WO2023071648A1 - 用于量子计算的光学装置、系统、方法及存储介质 - Google Patents

用于量子计算的光学装置、系统、方法及存储介质 Download PDF

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WO2023071648A1
WO2023071648A1 PCT/CN2022/120888 CN2022120888W WO2023071648A1 WO 2023071648 A1 WO2023071648 A1 WO 2023071648A1 CN 2022120888 W CN2022120888 W CN 2022120888W WO 2023071648 A1 WO2023071648 A1 WO 2023071648A1
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photons
photon
module
lens
feedforward
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PCT/CN2022/120888
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English (en)
French (fr)
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维夫莱什卡米哈尔
沃尔特菲利普
勒希鲍默伊丽莎白
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腾讯科技（深圳）有限公司
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Publication of WO2023071648A1 publication Critical patent/WO2023071648A1/zh
Priority to US18/144,508 priority Critical patent/US20230318716A1/en

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    • 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
    • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication
    • 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
    • G06N10/70—Quantum error correction, detection or prevention, e.g. surface codes or magic state distillation

Definitions

  • the embodiments of the present application relate to the technical field of quantum computing, and in particular to an optical device, system, method and storage medium for quantum computing.
  • Measurement Based Quantum Computing is a quantum computing method based on highly entangled cluster states as quantum computing resources.
  • the measurement-based quantum computing method measures the polarization states of multiple photons through a photosensitive element. Due to the entanglement between the quanta of the cluster state, each measured quantum will measure a random result, which has an impact on the next quanta to be measured, and is fed forward to the subsequent quantum according to the measurement result of the previous quantum.
  • the measurement results can obtain more accurate values.
  • Embodiments of the present application provide an optical device, system, method, and storage medium for quantum computing, which can reduce the number of active optical elements used to measure quantum data and reduce costs. Described technical scheme is as follows:
  • an optical device for quantum computing includes: a delay generation module, an optical fiber collimation module, a quasi-spatial mode generation module and a feedforward measurement module,
  • the feedforward measurement module includes an active optical element for modulating the optical signal;
  • the delay generating module is used to generate different time delays for n photons respectively, so that the n photons respectively arrive at the active optical element at different times, and n is an integer greater than 1;
  • the optical fiber collimation module is used to convert the light of the n photons into n-way collimated light to propagate in free space;
  • the quasi-spatial mode generation module is used to control the light rays of the n photons propagating in free space to pass through the same active optical element in turn, and the active optical element is used to control the light rays of the n photons according to the n photon Arriving at the time sequence of the active optical element, sequentially performing modulation processing on the optical signals of the n photons;
  • the feedforward measurement module is used to measure the polarization of the modulated optical signal of the first photon to obtain the measurement result of the first photon, and the measurement result of the first photon is used to measure the Feedforward compensation or feedforward error correction is performed on the measurement result of the second photon; wherein, the first photon is one of the n photons, and the second photon is the next photon of the first photon Measured photons.
  • a quantum computing system includes the above-mentioned optical device for quantum computing.
  • a multi-photon mode active optical feed-forward method is provided, the method is applied in an optical device for quantum computing, and the device includes: a delay generation module, an optical fiber quasi- A direct module, a quasi-spatial mode generation module, and a feedforward measurement module, wherein the feedforward measurement module includes an active optical element for modulating an optical signal;
  • the methods include:
  • n is an integer greater than 1;
  • the light rays of the n photons propagating in free space are controlled by the quasi-spatial mode generation module, and pass through the same active optical element in sequence, and the active optical element is used to arrive at the n photons according to the
  • the time sequence of the active optical elements is to sequentially perform modulation processing on the optical signals of the n photons;
  • the polarization measurement of the modulated optical signal of the first photon is carried out by the feedforward measurement module to obtain the measurement result of the first photon, and the measurement result of the first photon is used to measure the first photon to be measured.
  • Feedforward compensation or feedforward error correction is performed on the measurement results of two photons; wherein, the first photon is one of the n photons, and the second photon is the next one of the first photon to be measured of photons.
  • a computer-readable storage medium is provided, and a computer program is stored in the computer-readable storage medium, and the computer program is loaded and executed by a processor to implement the above-mentioned multiple Active Optical Feedforward Approach for Photonic Modes.
  • a computer program product includes a computer program, the computer program is loaded and executed by a processor to realize the active optical mode of the multi-photon mode as described above Feedforward approach.
  • multiple photons that are entangled with each other in the cluster state have different time delays; and through the quasi-spatial mode generation module, multiple photons are in a quasi-spatial mode that is very close in spatial distance but does not overlap,
  • the system only needs to use one active optical element to complete several fast feed-forward operations, realize the measurement of multiple photons respectively, and obtain the measurement results corresponding to the multiple photons respectively.
  • the time delay of multiple photons is different, so that different photons arrive at the feedforward measurement module at different times.
  • the feedforward measurement module uses the time interval between the arrival of adjacent photons to measure the photons to obtain the measurement results, and based on the measurement results, the system adjustment to achieve feed-forward compensation or correction. Since the same feed-forward measurement module can measure measurements between multiple photons in an entangled state, the number of active optical elements used in the calculation process is reduced, which helps to reduce the design difficulty of quantum devices, and Reduce the cost of quantum devices.
  • the feedforward measurement module can perform feedforward operations at high speed without reducing the speed and calculation accuracy of quantum computing and in cryptographic protocols. The security of the situation will have no impact on the speed or ubiquity of quantum computing.
  • Fig. 1 is a structural block diagram of an optical device for quantum computing provided by an embodiment of the present application
  • FIG. 2 is a schematic diagram of the positional relationship between photons and light rays provided by an embodiment of the present application
  • Fig. 3 is a schematic diagram of three lens modules in the quasi-spatial pattern generation module provided by an embodiment of the present application;
  • Fig. 4 is a schematic structural diagram of an optical device for quantum computing provided by an embodiment of the present application.
  • Fig. 5 is a schematic diagram of the composition of the feedforward measurement module and the relationship between the angle of the Pockels cell and the light intensity provided by one embodiment of the present application;
  • Fig. 6 is a schematic diagram of the relationship between the intensity function measured by the photodiode and the angle of the Pockels cell provided by an embodiment of the present application.
  • Quantum computing based on measurement Encode the calculation process in a specific complex entangled state, and realize quantum computing by operating and measuring this entangled state in a specific order, including quantum state adjustment.
  • MBQC is based on the highly entangled cluster state as the resource state of quantum computing. The computation itself is performed by continuously measuring neighboring qubits from the cluster state.
  • the sequence of measurements, together with the measurement devices, define computer systems that enable universal quantum computing by efficiently enabling arbitrary one-qubit and two-qubit (or multi-qubit) operations.
  • Electro Optical Modulators (Electro Optical Modulators, EOM): It is made by using the electro-optic effect of certain electro-optic crystals, such as lithium niobate crystal (LiNbO 3 ), gallium arsenide crystal (GaAs) and lithium tantalate crystal (LiTaO 3 ). into the modulator.
  • the electro-optic effect means that when a voltage is applied to the electro-optic crystal, the refractive index of the electro-optic crystal will change, resulting in a change in the characteristics of the light wave passing through the crystal, and realizing the modulation of the phase, amplitude, intensity and polarization state of the optical signal.
  • AOM Acousto Optical Modulators It is a modulator that uses external modulation technology to control the change of laser beam intensity.
  • the modulation signal acts on the transducer in the form of an electrical signal (amplitude modulation), and then converts it into a wave field that changes in the form of an electrical signal.
  • the optical carrier is modulated to become an intensity-modulated wave that "carries" information. .
  • Electro-optic modulation Pockels Cells It is an electro-optic modulation device based on the Pockels effect.
  • the Pockels effect refers to the photoelectric phenomenon in which the refractive index of a specific crystal is proportional to the strength of an applied electric field. By controlling the external electric field, the refractive index in a certain direction is changed, so that the electro-optic modulation Pockels cell can work as a variable half-wave plate, thereby realizing the polarization state change.
  • the electro-optic modulation Pockels cell is placed between two vertical polarizers, light intensity modulation can be realized.
  • the Pockels effect can be divided into longitudinal Pockels effect and transverse Pockels effect.
  • the voltage application direction is parallel to the light propagation direction, it is called the longitudinal Pockels effect.
  • the transverse Pockels effect When the voltage application direction is perpendicular to the light propagation direction.
  • Feed forward is an information processing technique used to process data containing errors or incompleteness and provide meaningful answers. When the technology is applied to solve real-world problems, it can increase the speed at which information is processed.
  • Single Photon Detectors (Single Photon Detectors, SPD): It is an ultra-low noise device used to detect the smallest energy quantum of light - photon. Single-photon detectors can detect and count individual photons with enhanced sensitivity, especially for emerging applications where the achievable signal strength is only a few photon energies.
  • Optical collimator It is used to convert the transmitted light in the fiber into collimated light (parallel light), or couple the external parallel (approximately parallel) light into the single-mode fiber.
  • Fiber collimators can be based on the principle of precise positioning of pigtails and self-focusing lenses.
  • Wave plate It is an optical device that can generate an additional optical path difference (or phase difference) between two mutually perpendicular optical vibrations.
  • Waveplates are usually made of birefringent crystals such as quartz, calcite, or mica of precise thickness, with the optical axis parallel to the crystal surface.
  • Quarter-wave plate also known as "quarter retardation plate", it is a kind of phase difference between ordinary light and extraordinary light when light of a certain wavelength is incident vertically. 1/4 wavelength optics. In the optical path, it is often used to change linearly polarized light into circularly polarized light or elliptically polarized light; or conversely, to change circularly polarized light or elliptically polarized light into linearly polarized light.
  • This kind of wave plate is usually made of birefringent material parallel to the optical axis and cut into a parallel plane plate. Made of optically active materials that can rotate the plane of polarization of incident light A wave plate with odd multiples is also called a quarter wave plate.
  • Field Programmable Gate Array (Field Programmable Gate Array, FPGA): It is a programmable logic array, and its basic structure includes programmable input and output units, configurable logic blocks, digital clock management modules, embedded blocks Random access memory (Random Access Memory, RAM), wiring resources, embedded dedicated hard core, and embedded functional units in the bottom layer.
  • FPGA is a product of further development on the basis of programmable devices such as Programmable Array Logic (PAL) and Generic Array Logic (GAL). It emerged as a semi-custom circuit in the field of Application Specific Integrated Circuit (ASIC), which not only solves the shortcomings of custom circuits, but also overcomes the shortcomings of the limited number of original programmable device gates.
  • PAL Programmable Array Logic
  • GAL Generic Array Logic
  • FPGA has the characteristics of rich wiring resources, reprogrammable and high integration, and low investment, it has been widely used in the field of digital circuit design.
  • the FPGA design process includes algorithm design, code simulation and design, board machine debugging, the designer and the actual needs to establish the algorithm architecture, use electronic design automation (Electronic Design Automation, EDA) to establish a design scheme or write design code through hardware, and through code simulation Ensure that the design scheme meets the actual requirements, and finally carry out board-level debugging, and use the configuration circuit to download relevant files to the FPGA chip to verify the actual operation effect.
  • EDA Electronic Design Automation
  • Polarizing beam splitter referred to as "polarizing beam splitter” is a combination of polarizing beam splitters instead of traditional polarizers, so that the output of the filter becomes perpendicular to each other in vibration, and the spectra are mutually perpendicular Complementary two beams of polarized light, i.e. optics that create two channels. Combining multiple polarizing beam splitters can result in multi-channel birefringent filters. By adjusting each channel of the multi-channel birefringent filter so that the transmission bands of each channel are continuously distributed in the spectral region near the spectral line, a new type of video spectrometer can be obtained.
  • Integrated photonics chip It is a chip obtained by integrating the light-emitting properties of indium phosphide and the optical path capability of silicon into a single hybrid chip, which can be applied to photonics-based computer equipment to realize In the case of applying a voltage to indium phosphide, the light enters the waveguide of the silicon chip to generate a continuous laser beam to drive other silicon photonic devices.
  • This silicon-based laser technology could make photonics more widely used in computers, because large-scale silicon-based manufacturing techniques can greatly reduce costs.
  • the technology is still a long way from commercialization, it is believed that dozens or even hundreds of hybrid silicon lasers will be integrated on a single silicon chip along with other silicon photonics components in the future. This is a sign of the beginning of low-cost mass production of highly integrated silicon photonic chips.
  • Rayleigh Length In optics and laser science, Rayleigh distance or Rayleigh Range (Rayleigh Range) refers to the beam along its direction of travel, from its waist to the cross-section whose area is twice the area of the waist The distance, at this time the section radius is about 1.414 times the waist radius.
  • Active optical components refers to electronic components that change photon motion properties (such as polarization, amplitude, etc.) through electrical energy.
  • an active optical element refers to an electro-optic modulator or an acousto-optic modulator, such as an electro-optic modulation Pockels cell.
  • the driving feed-forward is based on field-programmable gate arrays driving ultra-high-speed active Optical components (1MHz), that is, each feedforward operation requires an active optical component.
  • active optical elements having the same number as the number of photons are required to respectively measure the plurality of photons to obtain measurement results of the plurality of photons.
  • the present application by shortening the spatial distance between light rays of photons, multiple photons can pass through the same active optical element, and the same active optical element can complete the feedforward measurement of multiple photons.
  • the number of active optical elements needed to be used in the feedforward operation is reduced.
  • multiple photons have different time delays.
  • an active optical element such as an electro-optic modulator
  • the polarization state of the photons will change through the refraction of the electro-optic crystal. Since the crystal structure in electro-optic crystals is not completely uniform, reducing the spatial distance of multiple photons in free space can make multiple photons respectively pass through an electro-optic modulator, and after being modulated by the electro-optic modulator, the polarization state
  • the amount of change is basically the same.
  • this solution can minimize the influence of the inhomogeneity of the electro-optic crystal of the active optical element (such as the electro-optic modulator) on the polarization of multiple photons. Since in the standard measurement-based quantum computing method, feedforward operation is also required, and qubits need to be delayed, so when the number of photons to be measured remains unchanged, this scheme will not generate additional time loss, and the calculation frequency limit.
  • feedforward operation is also required, and qubits need to be delayed, so when the number of photons to be measured remains unchanged, this scheme will not generate additional time loss, and the calculation frequency limit.
  • FIG. 1 shows a schematic diagram of an optical device for quantum computing provided by an embodiment of the present application.
  • the device can also be called a multi-photon mode active optical feed-forward system.
  • the device may include: a delay generation module 10 , an optical fiber collimation module 20 , a quasi-spatial mode generation module 30 and a feedforward measurement module 40 .
  • the feedforward measurement module 40 includes an active optical element 41 for modulating the optical signal.
  • the delay generation module 10 is used to generate different time delays for the n photons respectively, so that the n photons arrive at the active optical element 41 at different times, where n is an integer greater than 1.
  • Photon refers to the medium of electromagnetic interaction.
  • n photons are in a highly entangled cluster state.
  • a photon is also called a single photon, and a qubit preferably corresponds to a single photon.
  • the time delay is caused by the difference in propagation time length (ie length) of the n photons passing through the delay generation module 10 .
  • the propagation time of photon 1 in the delay generation module 10 is about 7.34*10 -7 s
  • the propagation time of photon 2 in the delay generation module 10 is about 1.47*10 -6 s
  • the propagation time of photon 3 in the delay generation module 10 The propagation time in is about 2.20*10 ⁇ 6 s, and since the propagation time of the three photons in the delay generating module 10 is different, the three photons have different time delays.
  • the time delay of a certain photon refers to the time difference between the time when the photon enters the delay generation module 10 and the time when it leaves the delay generation module 10, that is, the photon passes through the delay generation module 10 10 The length of time it takes to propagate.
  • the active optical element 41 refers to an electrical element capable of modulating photons, and the active optical element 41 includes at least one of the following: an electro-optic modulator and an acousto-optic modulator.
  • the delay generating module 10 generates different time delays for n photons, and the difference between the time delays between adjacent photons is the same, that is, between two adjacent photons, the previous photon is different from the next photon.
  • Photons differ by a delay factor ⁇ .
  • the size of the delay factor ⁇ depends on the speed of the feedforward operation, and the delay factor ⁇ is greater than or equal to the minimum time required to perform a feedforward operation.
  • the optical fiber collimation module 20 is used to transform the light of n photons into n channels of collimated light to propagate in free space.
  • n-paths of collimated light rays refer to n-paths of light rays that are parallel to each other and do not diverge.
  • Free space refers to the space in which photons freely propagate.
  • the free space can be an open space or a closed space, such as open spaces such as air and outer space, and closed spaces such as airtight chambers.
  • the fiber collimation module 20 at least includes: a pigtail and a lens.
  • the focal length of the lens is 10 mm in consideration of factors such as precise alignment and reduction of beam divergence.
  • the quasi-spatial mode generation module 30 is used to control the light rays of n photons propagating in free space, passing through the same active optical element 41 sequentially, and the active optical element 41 is used to reach the active optical element 41 according to the n photons In time sequence, the modulation processing is performed sequentially on the optical signal of n photons.
  • the quasi-spatial mode generation module 30 controls the spatial distance between the light of n photons, so that the light of n photons can pass through the same active optical element 41 sequentially.
  • the quasi-spatial mode generation module 30 can also adjust the propagating directions of the above n photons.
  • a ray of photons is referred to as a spatial pattern of photons, a photon path.
  • n 3, that is, there are 3 photons in a highly entangled cluster state, and the light rays of the 3 photons are aligned in a non-overlapping manner through the quasi-spatial mode generation module 30, that is, the 3 photons pass through
  • the combination of free space elements generates three quasi-spatial patterns.
  • three photons generate three quasi-spatial modes.
  • the propagation direction of the three photons is perpendicular to the screen and inward, and the cross-sections of the light rays 201, 202 and 203 corresponding to the three photons are arranged in a triangle, that is, the distance between the light cross-sections (especially their central points) Connect the lines to form a triangle. Every two rays are aligned parallel to each other in a non-overlapping manner, and this quasi-spatial pattern minimizes the difference in the propagation environment of the photons during propagation. It can be seen that the quasi-spatial mode generation module 30 can change the spatial position of light rays of n photons in free space, so that n photons can be modulated by the same active optical element.
  • the small spatial distance between the photons' rays allows these photons to pass through the same active optical element in the same small location area. Because the crystal structure of the electro-optic crystal in the active optical element is not completely uniform, in the same small position area, the crystal structure of the electro-optic crystal is basically the same, and the refractive power is similar. Therefore, multiple photons pass through the same active optical element in the same small area of the block, so that the modulation effect of these photons by the active optical element 41 is basically the same, which helps to avoid adding new system errors.
  • the feedforward measurement module 40 is used to measure the polarization of the modulated optical signal of the first photon to obtain the measurement result of the first photon, and the measurement result of the first photon is used to measure the second photon to be measured As a result, feed-forward compensation or feed-forward error correction is performed; wherein, the first photon is one of the n photons, and the second photon is the next photon to be measured after the measurement of the first photon is started or completed.
  • the first photon may be any photon except the last photon reaching the feedforward measurement module 40 among the n photons.
  • the feedforward measurement module 40 measures the optical signal of the first photon to obtain the measurement result of the first photon.
  • the measurement includes polarization information of the first photon.
  • the second photon is the next photon arriving at the feedforward measurement module 40 after the first photon among the n photons. Since the n photons are in a cluster state of mutual entanglement, the properties of the n photons affect each other, so the measurement result of the first photon has an influence on the measurement result of the second photon. According to relevant principles of quantum physics, before the measurement result of the first photon is obtained, the first photon has multiple measurement results with different probabilities. Once the feedforward measurement module 40 measures the first photon, the measurement result of the first photon will undergo probability collapse, and the measurement result will be converted from an uncertain result to a definite result.
  • the feedforward measurement module 40 is adjusted to realize compensation or correction.
  • the adjustment of the feed-forward measurement module 40 based on the measurement of the first photon is performed by a rapidly switching element.
  • the feedforward measurement module 40 can be adjusted based on the measurement result of the first photon through the wave plate and the active optical element 41 in the open and closed states, and the measurement result of the second photon to be measured can be adjusted. Feedforward compensation and feedforward error correction.
  • the wave plate is a quarter wave plate. In some cases, after being modulated by the active optical element 41 , the polarization state of the photon will be distorted, and the distorted polarization state of the photon can be transformed into a sinusoidal polarization state by a quarter-wave plate. After the second photon reaches the feedforward measurement module 40 , the second photon is measured by the adjusted feedforward measurement module 40 to obtain a measurement result of the second photon.
  • the speed at which the feedforward measurement module 40 performs the feedforward operation is controlled by the active optical element 41 and is preferably related to the working speed of the active optical element 41 or is further preferably controlled by the working speed of the active optical element 41 The speed is determined, and the maximum speed of the feedforward operation is further preferably the working speed of the active optical element 41 .
  • the switching state of the active optical element 41 is controlled by a fast FPGA board.
  • multiple photons that are entangled in a cluster state have different time delays through the delay generation module; Quasi-spatial patterns that are very close together but do not overlap each other.
  • the system only needs to use one active optical element to complete several fast feedforward operations, realize the measurement of multiple photons, and obtain multiple corresponding measurement results respectively.
  • the time delays corresponding to multiple photons are different, so that different photons arrive at the feedforward measurement module at different times.
  • the feedforward measurement module uses the time interval between the arrival of adjacent photons to perform a feedforward operation on the previous photon.
  • the same feed-forward measurement module is able to measure measurements between multiple photons in an entangled state, the number of active optical elements required is reduced while at least keeping the number of photons measured constant, effectively It helps to reduce the design difficulty of quantum devices and reduce the production cost of quantum devices.
  • the feedforward measurement module can perform feedforward operations at high speed without reducing the speed and calculation accuracy of quantum computing and in cryptographic protocols. The security of the situation will not affect the universality of quantum computing.
  • optical device for quantum computing will be described below through several embodiments.
  • the difference between the time delay of the first photon and the time delay of the second photon is related to the time consumption of the feedforward operation.
  • the feedforward operation is performed in the feedforward measurement module.
  • the feed-forward operation time consumption refers to the length of time it takes to perform the feed-forward operation on a single photon.
  • the time consumption of the feedforward operation is related to the speed of the feedforward operation.
  • the feedforward operation at least includes the process of measuring the polarization of a certain single photon and the process of adjusting the feedforward measurement module based on the measurement result of the single photon.
  • the time consumption of the feedforward operation is related to the processing time consumption of the active optical components.
  • the time consumption of the feedforward operation at least includes: the measurement time of the first photon by the feedforward measurement module and the modulation time of the photon by the active optical element.
  • the difference between the time delays of the first photon and the second photon is controlled by the delay generation module to make it equal to Or slightly longer than the measurement time of the first photon by the feedforward measurement module plus the modulation time of the photon by the active optical element, so that the optical device used for quantum computing can obtain the measurement result of the photon and perform the feedforward operation without interruption.
  • the quasi-spatial pattern generation module includes at least one lens module, which is used to converge the light of n photons and then emit it in the form of n-way collimated light, so that the n photons The spatial distance between the light rays decreases.
  • the quasi-spatial mode generation module When a certain photon passes through the quasi-spatial mode generation module, it needs to pass through at least one lens module, and the spatial position of the light of the photon is changed through the refraction of the lens module. It should be noted that, before the n photons enter the quasi-spatial mode generating module, they need to pass through the delay generating module. Therefore, the time when the n photons arrive at the quasi-spatial mode generating module is different. In some embodiments, when the quasi-spatial pattern generation module includes more than one lens module, n photons respectively pass through each lens module in the propagation direction sequentially in time sequence.
  • the n photons are respectively refracted by at least one lens module in the quasi-spatial mode generation module, so that the spatial positions of the light rays of the n photons in free space are closer, and the light rays are still kept parallel.
  • the light rays corresponding to these photons have a small spatial distance and do not completely coincide, which allows these photons to pass through the same active optical element.
  • these photons can pass through the active optical element from the same small position area, so the modulation effect of the active optical element on n photons is basically similar, and will not increase during the measurement of the measurement results corresponding to n photons New calculation error.
  • each lens module includes a first lens and a second lens; the first lens is used for converging light rays of n photons; the second lens is used for converging n photons after passing through the first lens The light is converted into n-way collimated light and emitted.
  • the first lens is a convex lens
  • the second lens is a concave lens.
  • the distance between the center point of the first lens 311 and the center point of the second lens 312 is equal to the focal length of the first lens 311 minus the focal length of the second lens 312 . Since the first lens 311 is a convex lens, when a certain photon passes through the first lens 311 , the light of the photon is deflected to the direction of the optical axis of the first lens 311 through the converging effect of the convex lens. The photon then continues to propagate and passes through the second lens 312 .
  • the second lens 312 is a concave lens
  • the light direction of the photon is changed through the divergence of the concave lens.
  • the photon light is kept parallel to the optical axis of the first lens 311 (or the second lens 312 ) before and after passing through the lens module 310 . After a certain photon passes through a lens module, the space distance between the light of the photon and the optical axis of the lens in the lens module decreases.
  • the first lens is a convex lens
  • the second lens is a concave lens.
  • the center point of the first lens 321 and the center point of the second lens 322 are The distance between them is equal to the focal length of the first lens 321 plus the focal length of the second lens 322 .
  • the spatial distances of light rays of n photons are respectively closer to the optical axis of the first lens 321 (or the second lens 322), that is, n The spatial distance between the light rays of photons is closer.
  • three groups of lens modules are set in the quasi-spatial pattern generation module, namely lens module 310 , lens module 320 and lens module 330 .
  • the first lens 311 is a convex lens
  • the second lens 312 is a concave lens
  • the first lens 321 is a convex lens
  • the second lens 322 is a convex lens
  • the first lens is a convex lens 331.
  • the second lens 332 is a concave lens.
  • Three lens modules are placed sequentially in the direction of photon propagation.
  • the n photons enter the quasi-spatial mode generation module in chronological order, and for any one of the n photons, the photon passes through the lens module 310 , the lens module 320 and the lens module 330 in the propagation direction in sequence.
  • the spatial distance between the light rays corresponding to the n photons (less than the diameter of the light rays of the photons) achieves a better effect of being close to each other and not overlapping.
  • the use of the above three lens modules can make the light rays of the three photons be at an appropriate spatial distance, and the light rays of the three photons are parallel to each other in a quasi-spatial mode.
  • the three photons can pass through the same active optical element 41 smoothly through the convergence of the above three lens modules.
  • the quasi-spatial modes of n photons are parallel to each other during the feedforward operation of n photons in sequence.
  • Arranging at least one lens module in the quasi-spatial mode generation module is beneficial to increase the Rayleigh distance and improve the fault tolerance of the optical device used for quantum computing.
  • the quasi-spatial mode generating module further includes other adaptive optical devices.
  • the other adaptive optical devices at least include: adaptive mirrors.
  • the adaptive mirror 340 is used to change the propagation direction of photons.
  • the direction in which the adaptive mirror 340 is placed is 45° to the propagation direction of the photons, and the propagation direction of the photons is rotated by 90° through the refraction of the adaptive mirror 340 .
  • Adaptive mirror 340 is capable of generating a large number of high quality quasi-spatial modes.
  • the delay generation module includes n fiber loops, which are in one-to-one correspondence with n photons; the n fiber loops are used to generate different time delays for the n photons respectively.
  • the n fiber loops have different fiber lengths.
  • the fiber loops corresponding to different photons have different fiber lengths. If the fiber loop corresponding to a certain photon is longer, the time delay of the photon will be greater; if the fiber loop corresponding to a photon is shorter, the photon’s time delay will be greater. The smaller the time delay.
  • the delay generation module includes three optical fiber loops. The lengths of the three optical fiber loops are 220m, 440m and 660m respectively, and the time delay is t(660)>t(440)>t(220).
  • t(660) refers to the time delay of photons propagating in a fiber loop with a length of 660m, and the time delay of photons can be controlled by changing the length of the fiber loop.
  • the difference in the time delay of the first photon and the second photon is referred to as a delay factor ⁇ .
  • the minimum value of the delay factor ⁇ is related to the operating speed of the active optical element. In some embodiments, the delay factor ⁇ is limited to 1/(1 MHz). If an active optical element with a faster working speed is used, the delay factor ⁇ can be set smaller.
  • the operating speed of the active optical element is allowed to reach the order of tens of megahertz, which can further reduce the value of the delay factor ⁇ , and the specific range of the delay factor ⁇ is not limited here.
  • the length of the optical fiber loop can be set according to the value range of the delay factor ⁇ .
  • the time delay of a certain photon is related to its corresponding optical fiber loop and the propagation speed of the photon. The optical fiber loop is used to control the different time delays of different photons, and try to avoid changing other properties of the photons, so that the photons reach the active optical components at different times, and the active optical components can modulate the photons in turn.
  • the fiber optic loop is isolated from ambient temperature. Since the temperature will affect the polarization state of the photons, isolating the fiber loop from the ambient temperature can avoid the change of the polarization state of the photons during the propagation of the fiber loop as much as possible, which will help to improve the optical device used for quantum computing. Accuracy of photon polarization measurements.
  • the fiber collimator module includes n fiber collimators, and the n fiber collimators correspond to n fiber loops one by one; the target fiber collimator in the n fiber collimators is used The purpose is to convert the light of photons in the target fiber loop into collimated light to propagate in free space; wherein, the target fiber loop is the fiber loop corresponding to the target fiber collimator among the n fiber loops.
  • the photon For a certain photon, the photon propagates in the corresponding fiber loop. After leaving the fiber loop, it passes through the target fiber collimator in the fiber collimation module. ejected from the reactor and propagate in free space.
  • the n fiber collimators can transform the light of n photons into n channels of collimated light, so that the light of any two photons is parallel to each other.
  • the feedforward measurement module includes: a first polarization beam splitter, an active optical element, a wave plate, a second polarization beam splitter, a detector, and a driver for the active optical element; the first polarization beam splitter The device is used to obtain photons in the first polarization state; the active optical element is used to change the polarization state of the photons in the first polarization state to obtain photons with a second polarization state; the wave plate and the second polarization beam splitter are used to obtain photons from the second polarization state At least one photon of a single polarization state is separated from the photons of the state; the detector is used to detect the light intensity of the photon of at least one single polarization state.
  • the first polarization beam splitter and the second polarization beam splitter are respectively used to filter out photons with a specific polarization state.
  • the first polarization beam splitter Taking the first polarization beam splitter as an example to filter out photons with horizontal polarization, the first polarization beam splitter only allows photons in the horizontal polarization state to continue propagating along the original propagation direction of the photons, so as to filter out photons with a specific polarization state photon effect.
  • the first polarization beam splitter can change the propagation direction of photons with other polarization states, or absorb these photons.
  • the first polarization beam splitter and the second polarization beam splitter may respectively filter out photons with the same polarization state, or may respectively filter out photons with different polarization states.
  • Active optical elements modulate photons by changing the polarization state of photons passing through them.
  • the distance between the n collimated rays formed by the light rays of the photons is very close, so that these photons pass through the same active optical element in the feedforward measurement module.
  • polarization rotation In some embodiments, in the case of quantum encoding based on polarization information, the active optical element may be an electro-optic modulator.
  • the refractive index of the electro-optic crystal in the electro-optic modulator can be changed, thereby affecting the vibrational state of the photons passing through the electro-optic modulator.
  • the optical intensity modulation can be achieved by adjusting the voltage of the electro-optic modulator, and the electro-optic modulator is equivalent to a half-wave plate .
  • the active optical element refers to an acousto-optic modulator.
  • the wave plate is a quarter wave plate, and the wave plate is rotated in steps of 5°.
  • the feedforward measurement module includes two detectors, and the two detectors are respectively used to detect single photons of different polarization states.
  • the detectors include photodiodes or other devices capable of detecting single photons.
  • the initial logic of the first detector is named "0" and the initial logic of the second detector is named "1".
  • the logical designation is the number used to distinguish the first detector from the second detector.
  • the measurement result of the feedforward measurement module is 0.
  • the group has a measurement of 1.
  • the logical naming of the first detector becomes 1 and the logical naming of the second detector becomes 0.
  • the measurement result of the feedforward measurement module is 1.
  • the measurement result is 0.
  • the feedforward measurement module after a certain photon enters the feedforward measurement module, it can sequentially pass through the first polarization beam splitter, the active optical element, the wave plate, the second polarization beam splitter, and finally reach the detector.
  • the optical device for quantum measurement provided by this application only needs to pass through a quarter-wave plate, an active optical element (such as a Pockels cell, etc.) and two detectors that can be interchangeably named logically. Realize the measurement of the rotation angle of single photon polarization.
  • an active optical element such as a Pockels cell, etc.
  • two detectors that can be interchangeably named logically. Realize the measurement of the rotation angle of single photon polarization.
  • the opportunity to measure four polarization angles of photons can be obtained.
  • the opportunity to measure the four polarization angles of photons is achieved by changing the switching state of the active optical element and exchanging the state of the first detector and the second detector respectively.
  • the specific method is as follows:
  • the number of measurable polarization angles can be increased by using more complex active optical element controllers, enabling the system to move closer to pervasive quantum computing.
  • FIG. 4 shows a schematic diagram of an optical device for quantum computing provided by an embodiment of the present application.
  • 3 highly entangled photons in the cluster state respectively enter the fiber loops of different lengths in the delay generation module (not shown in the figure) to propagate, and the fiber loops of different lengths make the 3 photons in the optical fiber Different propagation times in the loop create different time delays.
  • Photons enter the fiber collimation module 20 after leaving the delay generation module.
  • the fiber collimation module 20 includes at least 3 target fiber collimators 21.
  • the 3 photons enter the corresponding target fiber collimators respectively, and collimate through the fiber.
  • the detector converts the light of 3 photons into collimated light.
  • the light rays of the three photons propagate in free space parallel to each other, and enter the quasi-spatial pattern generation module 30 in a time sequence.
  • the quasi-spatial mode generation module 30 respectively passes through the three lens modules in the propagation direction in sequence.
  • the three photons pass through the convergence of the three lens modules 310 , 320 and 330 respectively to form quasi-spatial modes with close spatial distances and parallel to each other.
  • the spatial distances between the quasi-spatial modes corresponding to the three photons are very close and will not overlap.
  • the quasi-spatial pattern generation module 30 also includes other adaptive optical elements such as an adaptive plane mirror 340.
  • the adaptive flat mirror 340 is used to change the propagation direction of the photons; since the time delays generated by the three photons in the delay generation module are different, the moments when the three photons arrive at the feedforward measurement module 40 are different, and the feedforward measurement module 40 utilizes The difference between the delay times of the first photon and the second photon completes the feedforward operation on the first photon.
  • the first polarization beam splitter 42 in the feedforward measurement measurement module 40 only allows photons in a horizontally polarized state to pass through. After a certain photon passes through the first polarization beam splitter 42 , it continues to propagate in the original direction and reaches the active optical element 41 .
  • the active optical element 41 is an electro-optic modulator.
  • the refractive index of the electro-optic crystal in the electro-optic modulator can be changed, thereby changing the polarization state of the photon.
  • the modulated photons are filtered through the quarter-wave plate 43 with a step size of 5° and the second polarization beam splitter 44 successively.
  • the detector 45 is able to detect whether a certain photon has reached its surface. According to the detection result of the detector 45, the polarization of the photon can be determined, and a measurement result corresponding to the photon can be generated.
  • the optical fiber loop in the delay generation module adopts 780HP optical fiber with FC (Ferrule Connector)/PC (Physical Contact, physical contact) connector.
  • FC Ferule Connector
  • PC Physical Contact, physical contact
  • This optical fiber is at a given wavelength (800nm)
  • the loss is minimal
  • the delay factor ⁇ is determined as 1/(1MHz) by the speed of the feedforward operation.
  • the lengths of the three optical fiber loops are 220m, 440m and 660m respectively, and are used in optical devices for quantum computing
  • the type of fiber used depends on the wavelength of the qubit to be measured, and the length of the fiber loop depends on the speed at which the feedforward measurement module performs the feedforward operation.
  • the lenses in at least one of the lens modules in the quasi-spatial mode generation module are made of boron-coated ultraviolet silicon lens material, which can reduce the loss of photons passing through the lens.
  • each lens module for the parameters of the lens in the group please refer to Table 1, the design table of the lens group in the quasi-spatial mode generation module.
  • Pockels cell This system uses double KTP crystal Pockels cell.
  • the specifications of the Pockels cell are: crystal size: 6 ⁇ 6 ⁇ 10mm, diameter: 25.4mm, length: 42.2mm, CA diameter: 5.5mm, light transmittance>98%@790nm.
  • Pockels cell drive The specifications of the Pockels cell drive used in this system are: working voltage 2.9kV, repetition rate 1MHz.
  • FPQA The specifications of FPQA used in this system are: 1GB 1800Mbps onboard DDR3, fully populated 400-pin FMCH Pockels box interface, 5 Pmod ports.
  • the ray diameter of the photon and the quasi-spatial mode data corresponding to the three photons are measured by the laser and WinCamD (far-infrared spot analyzer) produced by DataRay.
  • the diameters d1, d2 and d3 of the three rays and the distance between the three rays D12 , D23 and D13 please refer to the relevant data of 500 in FIG. 5 for the serial numbers corresponding to the rays of the three photons and the positional relationship between the three rays), as shown below.
  • the first polarizing beam splitter 510 preceding the Kerr cell 520 is used to filter photons (filter out photons with a specific polarization state), ensuring that only initially horizontally polarized photons are part of the characterization. These photons then pass through a Pockels cell 520 and a half-wave plate 530 rotated in 5° steps.
  • the second polarizing beam splitter 540 filters (polarizes) the photons again before the photodiode 550 .
  • the photodiode 550 measures the intensity of the photon as the Pockels cell is turned on and off, and the Pockels cell 520 is determined by the phase between the two intensity functions. set the angle.
  • the reason for the different angles is the possible step size of the PCB motor of the controlled half-wave plate.
  • FIG. 6 shows the intensity function measured by the photodiode as a function of the rotation angle of the Pockels cell.
  • the amplitude of beam 1 is ⁇ 0.7
  • the amplitude of beam 2 is ⁇ 1.3
  • the amplitude of beam 3 is unchanged.
  • An exemplary embodiment of the present application provides a quantum computing system, which includes the optical device for quantum computing described in the above embodiments.
  • the system further includes an entangled photon generation module and a measurement error correction module.
  • the entangled photon generation module is used to generate photon clusters with n photons in a highly entangled state.
  • the entangled photon generation module at least includes: an ultraviolet generator and a photon generation crystal.
  • four photon clusters in a highly entangled state can be generated by irradiating the surface of the photon-generating crystal with an ultraviolet generator.
  • the measurement error correction module is used to correct the measurement results about photon polarization measured by the above-mentioned optical device for quantum computing.
  • the polarization information of a certain photon includes three components (quantum states) in spatial position.
  • the polarization information of a certain photon is stored in a certain component of the polarization information of the other two photons, and by performing quantum calculations on the polarization information of the other two photons, it can be determined If there is an error in the measurement of that photon, an error correction process is implemented.
  • An exemplary embodiment of the present application provides a multi-photon mode active optical feed-forward method, which is applied in an optical device for quantum computing, and the device includes: a delay generation module, an optical fiber collimation module, A quasi-spatial mode generation module and a feedforward measurement module, wherein the feedforward measurement module includes active optical elements for modulating and processing optical signals; the method may include the following steps:
  • the delay generation module generates different time delays for n photons, so that the n photons arrive at the active optical element at different times, and n is an integer greater than 1.
  • the light of n photons is converted into n channels of collimated light to propagate in free space.
  • the difference between the time delay of the first photon and the time delay of the second photon is related to the time consumption of the feedforward operation.
  • the quasi-spatial pattern generation module includes at least one lens module, and the lens module reduces the spatial distance between light rays of n photons.
  • the lens module is used for converging the light of n photons and then emitting it in the form of n channels of collimated light.
  • each lens module includes a first lens and a second lens; the first lens is used for converging light rays of n photons; the second lens is used for converging n photons after passing through the first lens The light is converted into n-way collimated light and emitted.
  • the first lens is a convex lens
  • the second lens is a concave lens or a convex lens
  • the delay generation module includes n fiber loops, which are in one-to-one correspondence with n photons; the n fiber loops are used to generate different time delays for the n photons respectively.
  • the n fiber loops have different fiber lengths.
  • the fiber collimator module includes n fiber collimators, and the n fiber collimators correspond to n fiber loops one by one; the target fiber collimator in the n fiber collimators is used The purpose is to convert the light of photons in the target fiber loop into collimated light to propagate in free space; wherein, the target fiber loop is the fiber loop corresponding to the target fiber collimator among the n fiber loops.
  • the delay generating module is isolated from ambient temperature so as to preserve the polarization state of each photon during the delay operation.
  • the feedforward measurement module includes: a first polarization beam splitter, an active optical element, a wave plate, a second polarization beam splitter, a detector, and a driver for the active optical element; the first polarization beam splitter The device is used to obtain photons in the first polarization state; the active optical element is used to change the polarization state of the photons in the first polarization state to obtain photons with a second polarization state; the wave plate and the second polarization beam splitter are used to obtain photons from the second polarization state At least one photon of a single polarization state is separated from the photons of the state; the detector is used to detect the light intensity of the photon of at least one single polarization state.
  • the active optical element includes an electro-optic modulator.
  • multiple photons that are entangled with each other in the cluster state have different time delays; and through the quasi-spatial mode generation module, multiple photons are in a quasi-spatial mode that is very close in spatial distance but does not overlap,
  • the system only needs to use one active optical element to complete several fast feed-forward operations, realize the measurement of multiple photons respectively, and obtain the measurement results corresponding to the multiple photons respectively.
  • the time delay of multiple photons is different, so that different photons arrive at the feedforward measurement module at different times.
  • the feedforward measurement module uses the time interval between the arrival of adjacent photons to measure the photons to obtain the measurement results, and based on the measurement results, the system adjustment to achieve feed-forward compensation or correction.
  • the same feed-forward measurement module is able to measure measurements between multiple photons in an entangled state, the number of active optical elements used in the calculation is reduced while the number of measured photons remains at least the same , help to reduce the design difficulty of quantum equipment, and reduce the cost of quantum equipment.
  • the embodiment of the present application also provides a computer-readable storage medium, where a computer program is stored in the computer-readable storage medium, and the computer program is loaded and executed by a processor to realize the multi-photon active optical mode provided by the above-mentioned method embodiments. Feedforward approach.
  • the computer-readable storage medium may include: ROM (Read-Only Memory, read-only memory), RAM (Random-Access Memory, random access memory), SSD (Solid State Drives, solid state drive) or an optical disc, etc.
  • the random access memory may include ReRAM (Resistance Random Access Memory, resistive random access memory) and DRAM (Dynamic Random Access Memory, dynamic random access memory).
  • the embodiment of the present application also provides a computer program product, the computer program product includes a computer program, and the computer program is loaded and executed by a processor to implement the multi-photon mode active optical feedforward method provided by the implementation of the above methods.
  • the "plurality” mentioned herein refers to two or more than two.
  • the numbering of the steps described herein only exemplarily shows a possible sequence of execution among the steps.
  • the above-mentioned steps may not be executed according to the order of the numbers, such as two different numbers The steps are executed at the same time, or two steps with different numbers are executed in the reverse order as shown in the illustration, which is not limited in this embodiment of the present application.

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Abstract

本申请公开了一种用于量子计算的光学装置、系统、方法及存储介质，涉及量子计算技术领域。所述装置包括：延迟产生模组（10），用于对n个光子分别产生不同的时间延迟，使得n个光子分别在不同的时刻到达有源光学元件；光纤准直模组（20），用于将n个光子的光线转变成n路准直光传播；准空间模式产生模组（30），用于使n个光子的光线依次经过同一个有源光学元件，有源光学元件用于按照n个光子到达的时间顺序，对n个光子的光信号依次进行调制处理；前馈测量模组（40），用于对经调制处理后的第一光子的光信号进行偏振测量，并得到测量结果，该结果用于对将被测量的第二光子的测量结果进行前馈补偿或前馈纠错。

Description

用于量子计算的光学装置、系统、方法及存储介质
本申请要求于2021年10月27日提交的、申请号为202111258194.1、发明名称为“用于量子计算的光学装置、系统及方法”的中国专利申请，以及于2021年10月29日提交的、申请号为202111272875.3、发明名称为“用于量子计算的光学装置、系统、方法及存储介质”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请实施例涉及量子计算技术领域，特别涉及一种用于量子计算的光学装置、系统、方法及存储介质。
背景技术
基于测量的量子计算(Measurement Based Quantum Computing，MBQC)是一种基于高度纠缠的团簇状态作为量子计算资源的量子计算方法。
相关技术中，基于测量的量子计算方法通过感光元件测量多个光子的偏振状态。由于团簇态的量子之间具有纠缠性，每一个被测量的量子会测量出一个随机的结果，这个结果对接下来需要测量的量子具有影响，根据前向量子的测量结果前馈到后续量子的测量结果，可以获得比较准确的数值。
然而，在相关技术中，需要通过大量用于测量量子的有源光学元件实现基于测量的量子计算，量子设备体积大，成本高。
发明内容
本申请实施例提供了一种用于量子计算的光学装置、系统、方法及存储介质，能够减少用于测量量子数据的有源光学元件的数量，降低成本。所述技术方案如下：
根据本申请实施例的一个方面，提供了一种用于量子计算的光学装置，所述装置包括：延迟产生模组、光纤准直模组、准空间模式产生模组和前馈测量模组，所述前馈测量模组中包括用于对光信号进行调制处理的有源光学元件；
所述延迟产生模组用于对n个光子分别产生不同的时间延迟，以使得所述n个光子分别在不同的时刻到达所述有源光学元件，n为大于1的整数；
所述光纤准直模组用于将所述n个光子的光线转变成n路准直光在自由空间中传播；
所述准空间模式产生模组用于控制在自由空间中传播的所述n个光子的光线，依次经过同一个所述有源光学元件，所述有源光学元件用于按照所述n个光子到达所述有源光学元件的时间顺序，对所述n个光子的光信号依次进行调制处理；
所述前馈测量模组用于对经调制处理后的第一光子的光信号进行偏振测量，得到所述第一光子的测量结果，所述第一光子的测量结果用于对将被测量的第二光子的测量结果进行前馈补偿或前馈纠错；其中，所述第一光子是所述n个光子中的一个光子，且所述第二光子是所述第一光子的下一个被测量的光子。
根据本申请实施例的一个方面，提供了一种量子计算系统，所述系统包括如上所述的用于量子计算的光学装置。
根据本申请实施例的一个方面，提供了一种多光子模式的有源光学前馈方法，所述方法在用于量子计算的光学装置中应用，所述装置包括：延迟产生模组、光纤准直模组、准空间模式产生模组和前馈测量模组，所述前馈测量模组中包括用于对光信号进行调制处理的有源光学元件；
所述方法包括：
通过所述延迟产生模组对n个光子分别产生不同的时间延迟，以使得所述n个光子分别在不同的时刻到达所述有源光学元件，n为大于1的整数；
通过所述光纤准直模组将所述n个光子的光线转变成n路准直光在自由空间中传播；
通过所述准空间模式产生模组控制在自由空间中传播的所述n个光子的光线，依次经过同一个所述有源光学元件，所述有源光学元件用于按照所述n个光子到达所述有源光学元件的时间顺序，对所述n个光子的光信号依次进行调制处理；
通过所述前馈测量模组对经调制处理后的第一光子的光信号进行偏振测量，得到所述第一光子的测量结果，所述第一光子的测量结果用于对将被测量的第二光子的测量结果进行前馈补偿或前馈纠错；其中，所述第一光子是所述n个光子中的一个光子，且所述第二光子是所述第一光子的下一个被测量的光子。
根据本申请实施例的一个方面，提供了一种计算机可读存储介质，所述计算机可读存储介质中存储有计算机程序，所述计算机程序由处理器加载并执行以实现如上面所述的多光子模式的有源光学前馈方法。
根据本申请实施例的一个方面，提供了一种计算机程序产品，所述计算机程序产品包括计算机程序，所述计算机程序由处理器加载并执行以实现如上面所述的多光子模式的有源光学前馈方法。
本申请实施例提供的技术方案可以带来如下有益效果：
通过延迟产生模组使得处于团簇状态相互纠缠的多个光子具有不同的时间延时；以及，通过准空间模式产生模组使得多个光子处于空间距离十分接近，但不重叠的准空间模式，使得本系统只需使用一个有源光学元件就能完成几次快速前馈操作，实现对多个光子分别进行测量，并分别获得多个光子对应的测量结果。利用多个光子的时间延迟不同，使得不同光子到达前馈测量模组的时刻不同，前馈测量模组利用相邻光子到达的时间间隔对光子进行测量得到测量结果，并基于测量结果对系统进行调整，实现前馈补偿或纠正。由于同一个前馈测量模组能够测量处于纠缠状态的多个光子之间的测量结果，因此减少了计算过程中使用的有源光学元件的数量，有助于降低了量子设备的设计难度，以及降低量子设备的成本。
另外，因为多个光子逐个到达前馈测量模组，光子之间到达的时间间隔较短，前馈测量模组能够高速进行前馈操作，不会降低量子计算的速率和计算精度以及在密码协议情况下的安全性，对量子计算的速度或普适性不会产生影响。
附图说明
图1是本申请一个实施例提供的用于量子计算的光学装置的结构框图；
图2是本申请一个实施例提供的光子的光线之间的位置关系的示意图；
图3是本申请一个实施例提供的准空间模式生成模组中三个镜头模组的示意图；
图4是本申请一个实施例提供的用于量子计算的光学装置的结构示意图；
图5是本申请一个实施例提供前馈测量模组的组成以及普克尔盒角度和光强关系的示意图；
图6是本申请一个实施例提供的光电二极管测得的强度函数与普克尔盒角度的关系的示意图。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合附图对本申请实施方式作进一步地详细描述。
在对本申请实施例进行介绍说明之前，首先对本申请中涉及的一些名词进行解释说明。
1.基于测量的量子计算：将计算过程编码于特定的复杂纠缠态，通过按特定顺序对这个纠 缠态进行操作和测量，包括量子态调整，而实现的量子计算。MBQC是基于高度纠缠的团簇状态(cluster state)来作为量子计算的资源状态(resource state)。计算本身是通过从团簇状态连续测量相邻量子比特来实现的。测量的顺序，连同测量装置一起，通过有效地实现任意的单量子比特和两量子比特(或多量子比特)运算，来定义实现通用量子计算的计算机系统。
2.电光调制器(Electro Optical Modulators，EOM)：是利用某些电光晶体，如铌酸锂晶体(LiNbO 3)、砷化稼晶体(GaAs)和钽酸锂晶体(LiTaO 3)的电光效应制成的调制器。电光效应即当把电压加到电光晶体上时，电光晶体的折射率将发生变化，结果引起通过该晶体的光波特性的变化，实现对光信号的相位、幅度、强度以及偏振状态的调制。
3.声光调制器(Acousto Optical Modulators，AOM)：是一种利用外调制技术控制激光束强度变化的调制器。调制信号是以电信号(调幅)形式作用于换能器上，再转化为以电信号形式变化的波场，当光波通过介质时，使光载波受到调制而成为“携带”信息的强度调制波。
4.电光调制普克尔盒(Pockels Cells)：是基于普克尔效应制作的电光调制器件。普克尔效应(pockels effect)指的是特定晶体折射率与外加电场强度成一定比例关系的光电现象。通过对外加电场的控制，从而改变一定方向的折射率，使得电光调制普克尔盒可以作为一个可变半波片工作，从而实现偏振态改变。当该电光调制普克尔盒置于两片垂直偏振片之间时，就可以实现光强调制。根据电压加压方向不同，普克尔效应又可分为纵向普克尔效应和横向普克尔效应。当电压加压方向平行与光传播方向时，称为纵向普克尔效应。当电压加压方向与光传播方向垂直时，称为横向普克尔效应。
5.前馈操作(feed forward operation)：前馈是一种信息处理技术，用于处理包含错误或不完整的数据，并提供有意义的答案。该技术被应用于解决现实世界的问题时，可以提高处理信息的速度。
6.单光子探测器(Single Photon Detectors，SPD)：是一种超低噪声器件，用于探测光的最小能量量子——光子。单光子探测器可以利用增强的灵敏度对单个光子进行探测和计数，尤其适用于可获得的信号强度仅为几个光子能量级的新兴应用中。
7.光纤准直器(Optical Collimator)：用于将光纤内的传输光转变成准直光(平行光)，或将外界平行(近似平行)光耦合至单模光纤内。光纤准直器可基于尾纤与自聚焦透镜精确定位的原理。
8.波片(wave plate)：是能使互相垂直的两光振动间产生附加光程差(或相位差)的光学器件。波片通常由具有精确厚度的石英、方解石或云母等双折射晶片做成，其光轴与晶片表面平行。
9.四分之一波片(quarter-wave plate)：又称“四分之一推迟板”，是一种使得一定波长的光垂直入射通过时，出射的寻常光和异常光之间相位差1/4波长的光学器件。在光路中它常用来使线偏振光变为圆偏振光或椭圆偏振光；或者相反，用来使圆偏振光或椭圆偏振光变为线偏振光。这种波片通常采用双折射材料沿平行于光轴方向切割制成平行平面板，其厚度应精确地为双折射材料两个主轴折射率差和给定波长1/4的乘积的奇数倍。用旋光材料制成的能使入射光偏振面旋转
Figure PCTCN2022120888-appb-000001
的奇数倍的波片也称为四分之一波片。
10.现场可编程逻辑门阵列(Field Programmable Gate Array，FPGA)：是一种可编程的逻辑列阵，其基本结构包括可编程输入输出单元，可配置逻辑块，数字时钟管理模块，嵌入式块随机存取存储器(Random Access Memory，RAM)，布线资源，内嵌专用硬核，底层内嵌功能单元。FPGA是在可编程阵列逻辑(Programmable Array Logic，PAL)、通用逻辑阵列(Generic Array Logic，GAL)等可编程器件的基础上进一步发展的产物。它是作为专用集成电路(Application Specific Integrated Circuit，ASIC)领域中的一种半定制电路而出现的，既解决了定制电路的不足，又克服了原有可编程器件门电路数有限的缺点。由于FPGA具有布线资源丰富，可重复编程和集成度高，投资较低的特点，在数字电路设计领域得到了广泛的应用。FPGA的设计流程包括算法设计、代码仿真以及设计、板机调试，设计者以及实际需求建立算 法架构，利用电子设计自动化(Electronic Design Automation，EDA)建立设计方案或通过硬件编写设计代码，通过代码仿真保证设计方案符合实际要求，最后进行板级调试，利用配置电路将相关文件下载至FPGA芯片中，验证实际运行效果。
11.偏振射束分离器(polarizing beam splitter)：简称为“偏振分束器”，是一种利用组合偏振光束分离器代替传统的偏振片，使滤光器的出射成为振动彼此垂直，光谱彼此互补的两束偏振光，即产生两个通道的光学器件。使用多个偏振分束器进行组合，能得到多通道双折射滤光器。调节多通道双折射滤光器的各个通道，使各个通道透过带连续分布于谱线附近光谱区，能够得到新型的视频光谱仪。
12.集成光子芯片(integrated photonics chip)：是一种通过将磷化铟的发光属性和硅的光路进行能力整合到单一混合芯片中得到的芯片，可应用于基于光子学的计算机设备中，实现在对磷化铟施加电压的情况下，使得光进入硅片的波导，产生持续的激光束，驱动其它的硅光子器件的效果。这种基于硅片的激光技术可使光子学更广泛地应用于计算机中，因为采用大规模硅基制造技术能够大幅度降低成本。尽管该技术离商品化仍有很长距离，但相信未来数十个、甚至数百个混合硅激光器会和其它硅光子学部件一起，被集成到单一硅基芯片上去。这是开始低成本大批量生产高集成度硅光子芯片的标志。
13.瑞利距离(Rayleigh Length)：在光学及激光科学中，瑞利距离或瑞利范围(Rayleigh Range)是指光束沿着其行进方向，从其腰部到其面积为腰部面积两倍的截面的距离，此时截面半径约为1.414
Figure PCTCN2022120888-appb-000002
倍的腰部半径。
14.有源光学元件：是指通过电能改变光子运动属性(如偏振、振幅等)的电子元件。在本申请中，有源光学元件是指电光调制器或声光调制器，如电光调制普克尔盒。
在基于测量的量子计算框架下，以高度纠缠的团簇状态的量子作为计算资源，在一种前馈测量结果的纠错方法中，驱动前馈是基于现场可编程门阵列驱动超高速有源光学元件(1MHz)来实现的，即每进行一次前馈操作，都需要一个有源光学元件。相关技术中，对多个光子进行测量时，需要与光子数目相同的有源光学元件分别对多个光子进行测量，获得多个光子的测量结果。本申请通过缩短光子的光线之间的空间距离，使得多个光子能够穿过同一个有源光学元件，同一个有源光学元件能够完成对多个光子的前馈测量。出于改变量子计算结构的目的，本申请中为了减少前馈操作中需要使用的有源光学元件的数量。通过为多个光子设定不同的传播路径长度，使得多个光子具有不同的时间延迟。光子在有源光学元件(如电光调制器)中传播时，经过电光晶体的折射作用，光子的偏振状态会发生改变。由于电光晶体中晶体结构不是完全均匀的，缩小多个光子的光线在自由空间中的空间距离能够使得多个光子分别穿过某个电光调制器，并被该电光调制器调制后，偏振状态的变化量基本相同。由此，本方案可以将有源光学元件(如电光调制器)的电光晶体不均匀性对多个光子偏振情况造成的影响降到最低。由于在标准的基于测量的量子计算方法中，也需要进行前馈操作，需要对量子比特进行延迟，因此在待测量光子数量不变的情况下，本方案不会产生额外的时间损失，以及计算频率限制。下面通过几个实施例对本申请技术方案进行介绍说明。
请参考图1，其示出了本申请一个实施例提供的用于量子计算的光学装置的示意图。可选地，该装置也可以称为多光子模式的有源光学前馈系统。该装置可以包括：延迟产生模组10、光纤准直模组20、准空间模式产生模组30和前馈测量模组40。前馈测量模组40中包括用于对光信号进行调制处理的有源光学元件41。
延迟产生模组10用于对n个光子分别产生不同的时间延迟，以使得n个光子在不同的时刻到达有源光学元件41，n为大于1的整数。
光子是指电磁相互作用的媒介。在一些实施例中，n个光子处于高度纠缠的团簇状态。在本方案中，一个光子也称为单光子，一个量子比特优选地对应于一个单光子。在一些实施例 中，使用n＝3的光子进行测试，证明了本系统不会引入其它误差，n可以取更大的数值，本申请对n的最大范围不进行限定。
时间延迟是由于n个光子在通过延迟产生模组10过程中的传播时间长度(即时长)不同导致的。例如，在n＝3的情况下，光子1、光子2和光子3处于高度纠缠的团簇状态。光子1在延迟产生模组10中的传播时长约为7.34*10 -7s，光子2在延迟产生模组10中的传播时长约为1.47*10 -6s，光子3在延迟产生模组10中的传播时长约为2.20*10 -6s，由于3个光子在延迟产生模组10中的传播时长不同，使得3个光子具有不同的时间延迟。在本申请实施例中，某一光子的时间延迟，是指该光子从进入延迟产生模组10的时刻到离开延迟产生模组10的时刻之间的时间差，也即该光子在延迟产生模组10中传播所消耗的时长。
有源光学元件41是指能够对光子进行调制的用电元件，有源光学元件41至少包括以下之一：电光调制器、声光调制器。
在一些实施例中，延迟产生模组10对n个光子产生不同的时间延迟，相邻光子之间的时间延迟之差相同，也即相邻两个光子之间，前一个光子相对于后一个光子相差一个延迟因子τ。延迟因子τ的大小取决于前馈操作的速度，延迟因子τ大于或等于执行一次前馈操作所需的最小时间。相邻两个光子是指n个光子中，时间延迟最接近的两个光子，例如n＝4，光子A的时间延迟约为1.51*10 -6s、光子B时间延迟约为4.56*10 -6s、光子C时间延迟约为3.02*10 -6s、光子D时间延迟约为7.15*10 -6s，光子A和光子C是相邻光子，光子B和光子C是相邻光子，并且光子B和光子D是相邻光子。
光纤准直模组20用于将n个光子的光线转变成n路准直光在自由空间中传播。
上述n路准直光是指相互平行不会发散的n路光线。自由空间是指光子在其中自由传播的空间，自由空间可以是开放空间，也可以是封闭空间，例如空气、外层空间等开放空间，密闭腔室等封闭空间。在一些实施例中，光纤准直模组20中至少包括：尾纤和透镜。可选地，出于对精密对准、减少光束发散等因素的考虑，透镜的焦距为10mm。
准空间模式产生模组30用于控制在自由空间中传播的n个光子的光线，依次经过同一个有源光学元件41，有源光学元件41用于按照n个光子到达有源光学元件41的时间顺序，对n个光子的光信号依次进行调制处理。
在一些实施例中，准空间模式产生模组30通过控制n个光子的光线之间的空间距离，使得n个光子的光线能够依次经过同一个有源光学元件41。可选地，准空间模式产生模组30还能够调整上述n个光子的传播方向。在一些实施例中，光子的光线称为光子的空间模式、光子路径。
在一些实施例中，n＝3，即有3个光子处于高度纠缠的团簇状态，通过准空间模式产生模组30使得3个光子的光线以不重叠的方式对齐，也即3个光子通过自由空间元素组合生成了3个准空间模式。通过准空间模式产生模组30，3个光子生成了3个准空间模式。如图2所示，3个光子的传播方向为垂直于屏幕向内，3个光子分别对应的光线201、202和203的截面呈三角形排列，即光线截面(特别是其中心点)之间的连线形成三角形。每两个光线之间以不重叠的方式相互平行对齐，这种准空间模式使得光子在传播过程中的传播环境的差异最小。由此可见，准空间模式产生模组30能够改变n个光子的光线在自由空间中的空间位置，使得n个光子能够通过同一个有源光学元件进行调制。光子的光线之间的空间距离很小(光子的光线之间的空间距离能够小于光线的直径)，这使得这些光子能够在同一个块很小的位置区域穿过同一个有源光学元件。因为有源光学元件中电光晶体的晶体结构不是完全均匀的，在同一很小的位置区域中，电光晶体的晶体结构基本相同，折射能力相近。因此，多个光子在同一个块很小的位置区域穿过同一个有源光学元件，使得这些光子受到有源光学元件41的调制作用基本相同，有助于避免增加新的系统误差。
前馈测量模组40用于对经调制处理后的第一光子的光信号进行偏振测量，得到第一光子的测量结果，第一光子的测量结果用于对将被测量的第二光子的测量结果进行前馈补偿或前 馈纠错；其中，第一光子是n个光子中的一个光子，且第二光子是开始或者完成第一光子的测量以后的下一个被测量的光子。
第一光子可以是n个光子中，除了最后一个达到前馈测量模组40的光子之外的任意一个光子。前馈测量模组40对第一光子的光信号进行测量，得到第一光子的测量结果。在一些实施例中，测量结果包括第一光子的偏振信息。
第二光子是n个光子中，继第一光子之后，下一个到达前馈测量模组40的光子。由于n个光子之间处于相互纠缠的团簇状态，n个光子之间的属性相互影响，因此第一光子的测量结果对第二光子的测量结果具有影响。根据量子物理的相关原理，在没有获得第一光子的测量结果之前，第一光子具有不同概率的多种测量结果。一旦前馈测量模组40对第一光子进行测量，第一光子的测量结果会发生概率塌缩，测量结果由不确定转换成确定的某个结果。由于第一光子与第二光子处于纠缠状态，因此第一光子的测量结果对第二光子的测量结果有影响。基于第一光子的测量结果对前馈测量模组40进行调整，实现补偿或纠正。
在一些实施例中，基于第一光子的测量结果对前馈测量模组40调整，通过能够快速开关的元件来进行。可选地，通过波片和处于打开、关闭状态的有源光学元件41，可以实现基于第一光子的测量结果对前馈测量模组40进行调整，对即将测量的第二光子的测量结果进行前馈补偿和前馈纠错。在一些实施例中，波片为四分之一波片。在一些情况下，通过有源光学元件41的调制后，光子的偏振状态会发生畸变，通过四分之一波片能够将畸变的光子偏振状态转变正弦的偏振状态。在第二光子到达前馈测量模组40后，通过调整后的前馈测量模组40对第二光子进行测量，获得第二光子的测量结果。
在一些实施例中，前馈测量模组40进行前馈操作的速度通过有源光学元件41控制且优选地与有源光学元件41的工作速度有关或进一步优选地由有源光学元件41的工作速度决定，前馈操作的速度最大值更进一步优选地为有源光学元件41的工作速度。在一些实施例中，有源光学元件41的开关状态通过快速FPGA板控制。
综上所述，一方面，通过延迟产生模组使得处于团簇状态相互纠缠的多个光子具有不同的时间延时；另一方面，通过准空间模式产生模组使得多个光子的光线处于空间距离十分接近，但相互之间不重叠的准空间模式。本系统只需使用一个有源光学元件就能够完成几次快速前馈操作，实现对多个光子进行测量，并分别获得多个对应的测量结果。多个光子分别对应的时间延迟不同，使得不同光子到达前馈测量模组的时刻不同，前馈测量模组利用相邻光子到达的时间间隔对前一个光子的前馈操作。由于同一个前馈测量模组能够测量处于纠缠状态的多个光子之间的测量结果，因此在所测量的光子数量至少保持不变的情况下减少了所需要的有源光学元件的数量，有助于降低量子设备的设计难度，以及降低量子设备的制作成本。
另外，因为多个光子逐个到达前馈测量模组，光子之间到达的时间间隔较短，前馈测量模组能够高速进行前馈操作，不会降低量子计算的速率和计算精度以及在密码协议情况下的安全性，对量子计算的普适性不会产生影响。
下面通过几个实施例对量子计算的光学装置进行介绍说明。
在一些实施例中，第一光子的时间延迟和第二光子的时间延迟之间的差值，与前馈操作的耗时有关。
前馈操作在前馈测量模组中进行。在一些实施例中，前馈操作耗时是指对单光子进行前馈操作耗费的时长。前馈操作的耗时与前馈操作的速度有关，前馈操作至少包括对某个单光子偏振的测量过程和基于该单光子的测量结果对前馈测量模组进行调整的过程。前馈操作的耗时与有源光学元件的处理耗时有关。前馈操作的耗时至少包括：前馈测量模组对第一光子的测量时间和有源光学元件对光子的调制时间。为了进一步降低用于量子计算的光学装置在获取n个光子的测量结果过程中产生的延时，通过延迟产生模组控制第一光子与第二光子的时间延迟之间的差值，使其等于或略大于前馈测量模组对第一光子的测量时间加上有源光学 元件对光子的调制时间，使得用于量子计算的光学装置能够不间断地获得光子的测量结果和进行前馈操作。
在一些实施例中，准空间模式产生模组包括至少一个镜头模组，镜头模组用于对n个光子的光线产生会聚作用之后再以n路准直光的形式射出，以使得n个光子的光线之间的空间距离减小。
某个光子在穿过准空间模式产生模组的过程中，需要通过至少一个镜头模组，经过镜头模组的折射作用，该光子的光线的空间位置发生改变。需要说明的是，在n个光子进入准空间模式产生模组之前，需要先通过延迟产生模组，因此，n个光子到达准空间模式产生模组的时刻不同。在一些实施例中，在准空间模式产生模组中包括一个以上镜头模组的情况下，n个光子分别按时间先后顺序依次经过传播方向上的各个镜头模组。n个光子在准空间模式产生模组中分别经过至少一个镜头模组的折射作用，使得n个光子的光线在自由空间中的空间位置更接近，并且光线之间依旧保持平行。这些光子分别对应的光线之间的空间距离很小，并且不完全重合，这使得这些光子能通过同一个有源光学元件。进一步地，这些光子能够从同一块很小的位置区域通过有源光学元件，因此有源光学元件对n个光子的调制作用基本相似，在测量n个光子对应的测量结果的过程中不会增加新的计算误差。
在一些实施例中，每个镜头模组包括第一透镜和第二透镜；第一透镜用于对n个光子的光线产生会聚作用；第二透镜用于将经过第一透镜之后的n个光子的光线，转换为n路准直光的形式射出。
在一个示例中，在某个镜头模组中，第一透镜为凸透镜，第二透镜为凹透镜。如图3中的镜头模组310所示，第一透镜311中心点和第二透镜312中心点之间的距离等于第一透镜311的焦距减去第二透镜312焦距。由于第一透镜311是凸透镜，当某个光子穿过第一透镜311时，通过凸透镜的会聚作用，该光子的光线偏向第一透镜311光轴的方向。随后该光子继续传播并穿过第二透镜312。由于第二透镜312是凹透镜，通过凹透镜的发散作用，该光子的光线方向发生转变。在一些实施例中，光子的光线在经过镜头模组310前后，与第一透镜311(或第二透镜312)的光轴保持平行。某个光子通过一个镜头模组后，该光子的光线与镜头模组中透镜的光轴间的空间距离减小。
在另一个示例中，某个镜头模组中，第一透镜为凸透镜，第二透镜为凹透镜，如图3中镜头模组320所示，第一透镜321中心点与第二透镜322中心点之间的距离等于第一透镜321的焦距加上第二透镜322的焦距。可选地，经过第一透镜321和第二透镜322的会聚作用，使得n个光子的光线的空间距离分别与第一透镜321(或第二透镜322)的光轴更接近，也即n个光子的光线间的空间距离更加接近。
如图3所示，在一些实施例中，在准空间模式产生模组中设置3组镜头模组，分别为镜头模组310、镜头模组320和镜头模组330。其中，镜头模组310中第一透镜311为凸透镜，第二透镜312为凹透镜；镜头模组320中第一透镜321为凸透镜，第二透镜322为凸透镜；镜头模组330中第一透镜为凸透镜331，第二透镜332为凹透镜。三个镜头模组依次放置在光子的传播方向上。n个光子按照时间先后顺序进入准空间模式产生模组，对于n个光子中的任意一个光子，该光子依次经过传播方向上的镜头模组310、镜头模组320和镜头模组330。经过各个镜头模组的会聚作用，使得n个光子分别对应的光线之间的空间距离(小于光子的光线直径)达到相互接近且不重叠的较好效果。经过多次实验，在n＝3的情况下，使用上述3个镜头模组可以使得3个光子的光线之间处于合适的空间距离，且3个光子的光线之间相互平行处于准空间模式。3个光子通过上述3个镜头模组的会聚作用能够顺利通过同一个有源光学元件41。
前馈测量模型依次对n个光子进行前馈操作的过程中，n个光子的准空间模式是相互平行的。在准空间模式产生模组中设置至少一个镜头模组，有利于增大瑞利距离，提高用于量子计算的光学装置的容错能力。
在一些实施例中，准空间模式产生模组还包括其它自适应光学器件，可选地，其它自适应光学器件至少包括：自适应反射镜。如图4所示，自适应反射镜340用于改变光子的传播方向。在一些实施例中，将自适应反射镜340放置方向与光子的传播方向呈45°，通过自适应反射镜340的折射作用，使得光子的传播方向旋转90°。
通过自适应反射镜340改变光子的传播方向，能够有效缩短准空间模式产生模组的长度，有助于减小用于量子计算的光学装置的体积。自适应反射镜340能够产生大量高质量的准空间模式。
在一些实施例中，延迟产生模组包括n个光纤环路，n个光纤环路和n个光子一一对应；n个光纤环路用于对n个光子分别产生不同的时间延迟。
在一些实施例中，n个光纤环路具有不同的光纤长度。
不同光子对应的光纤环路具有的光纤长度不同，若某个光子对应的光纤环路越长，则该光子的时间延迟越大；若某个光子对应的光纤环路越短，则该光子的时间延迟越小。例如，在n＝3的情况下，延迟产生模组中包括三个光纤环路。三个光纤环路的长度分别为220m、440m和660m，时间延迟t(660)>t(440)>t(220)。以t(660)为例，t(660)是指在长度为660m的光纤环路中传播的光子的时间延迟，通过改变光纤环路的长度能够控制光子的时间延迟。在一些实施例中，第一光子和第二光子的时间延迟之差称为延迟因子τ。延迟因子τ的最小值和有源光学元件的工作速度有关，在一些实施例中，延迟因子τ被限制在1/(1MHz)。若使用工作速度更快的有源光学元件，则延迟因子τ可以设置的更小。目前技术状态中，有源光学元件的工作速度允许达到几十兆赫兹的量级，这能够进一步降低了延迟因子τ的取值，延迟因子τ的具体范围在此不进行限定。在一些实施例中，可以根据延迟因子τ的取值范围设定光纤环路的长度。在一些实施例中，某个光子的时间延迟与其对应的光纤环路以及光子的传播速度有关。光纤环路用于控制不同光子的具有不同的时间延迟，并且尽量避免改变光子的其它属性，使得光子达到有源光学元件的时间不同，有源光学元件能够依次对光子进行调制。
在一些实施例中，光纤环路与环境温度隔离。由于温度会对光子的偏振状态造成影响，将光纤环路与环境温度隔离，能够尽可能避免光子在光纤环路中传播过程中偏振状态发生改变，有助于提高用于量子计算的光学装置对光子偏振的测量结果的准确性。
在一些实施例中，光纤准直模组包括n个光纤准直器，n个光纤准直器和n个光纤环路一一对应；n个光纤准直器中的目标光纤准直器，用于将目标光纤环路中光子的光线转变成准直光在自由空间中传播；其中，目标光纤环路是n个光纤环路中与目标光纤准直器对应的光纤环路。
对于某个光子来说，该光子在对应的光纤环路中传播，离开该光纤环路后，通过光纤准直模组中的目标光纤准直器，该光子转变成准直光从目标准直器中射出，并在自由空间中传播。n个光纤准直器能够将n个光子的光线转变成n路准直光，使得任意两个光子的光线之间相互平行。
在一些实施例中，前馈测量模组包括：第一偏振分束器、有源光学元件、波片、第二偏振分束器、探测器和有源光学元件的驱动器；第一偏振分束器用于获得第一偏振状态的光子；有源光学元件用于改变第一偏振状态的光子的偏振状态，得到具有第二偏振状态的光子；波片和第二偏振分束器用于从第二偏振状态的光子中分离出至少一种单一偏振状态的光子；探测器用于探测至少一种单一偏振状态的光子的光强。
第一偏振分束器和第二偏振分束器分别用于过滤出具有特定偏振状态的光子。以第一偏振分束器用于过滤出具有水平偏振的光子为例，第一偏振分束器仅允许处于水平偏振状态的光子继续沿着光子原来传播方向进行传播，从而实现过滤出具有特定偏振状态的光子的效果。可选地，第一偏振分束器可以改变具有其它偏振状态的光子的传播方向，或将这些光子吸收。可选地，第一偏振分束器和第二偏振分束器可以分别过滤出具有相同偏振状态的光子，也可以分别过滤出具有不同偏振状态的光子。有源光学元件通过改变穿过其内部的光子的偏振状 态，实现了对光子的调制。由于n个光子分别通过准空间模式产生模组时，光子的光线形成的n路准直光线间的距离很接近，使得这些光子在前馈测量模组中的有源光学元件中经过了相同的偏振旋转。在一些实施例中，在基于偏振信息进行量子编码的情况下，有源光学元件可以是电光调制器。通过调节电光调制器两侧的电压，可以改变电光调制器中电光晶体的折射率，从而影响穿过电光调制器的光子的振动状态。在一些情况中，当电光调制器放置在两个相互垂直的偏振分束器之间，通过调节电光调制器的电压能够实现光强调制，此时电光调制器相当于一块二分之一波片。在另一些实施例中，在基于路径信息进行量子编码的情况下，有源光学元件是指声光调制器。在一些实施例中，波片是四分之一波片，并且该波片以5°的步长旋转。在一些实施例中，前馈测量模组中包括两个探测器，两个探测器分别用于探测不同偏振状态的单光子。可选地，探测器包括光电二极管或其他能够探测单光子的设备。第一探测器的初始逻辑命名为“0”，第二探测器的初始逻辑命名为“1”。逻辑命名是用于区别第一探测器和第二探测器的编号。在两个探测器处于初始逻辑命名的情况下，当第一探测器检测到单光子时，前馈测量模组的测量结果为0，当第二探测器检测到单光子时，前馈测量模组的测量结果为1。在改变两个探测器的逻辑命名后(相当于交换两个探测器的逻辑命名)，第一探测器的逻辑命名变为1，第二探测器的逻辑命名变为0。在交换两个探测器的逻辑命名后，当第一探测器检测到单光子时，前馈测量模组的测量结果为1，当第二探测器检测到单光子时，前馈测量模组的测量结果为0。通过交换第一探测器和第二探测器之间的命名在量子比特上实现了比特旋转门的功能，通过上述方法实现的量子旋转门，具有很快的运行速度，并且技术上容易实现。
在一些实施例中，某个光子进入前馈测量模组后，能够依次经过第一偏振分束器、有源光学元件、波片、第二偏振分束器，最终到达探测器。
本申请提供的用于量子测量的光学装置，只需要通过一个四分之一波片、一个有源光学元件(如普克尔盒等)和两个可以互换逻辑命名的探测器，就可以实现对单光子偏振的旋转角度进行测量。在一个实施例中，通过打开/关闭有源光学元件，交换第一探测器和第二探测器的逻辑命名，可以获得测量光子的四种偏振角度的机会。测量光子的四种偏振角度的机会通过分别变换有源光学元件的开关状态和交换第一探测器、第二探测器的状态实现，具体方式如下：
1.打开有源光学元件41，使用第一探测器、第二探测器的初始逻辑命名；
2.关闭有源光学元件41，使用第一探测器、第二探测器的初始逻辑命名；
3.打开有源光学元件41，交换第一探测器、第二探测器的初始逻辑命名；
4.关闭有源光学元件41，交换第一探测器、第二探测器的初始逻辑命名。
在一些实施例中，通过使用更加复杂的有源光学元件控制器能够增加可测量的偏振角度的数量，使得本系统能够向普适化量子计算靠拢。
请参考图4，其示出本申请一个实施例提供的用于量子计算的光学装置的示意图。
在一些实施例中，3个处于高度纠缠的团簇状态光子分别进入延迟产生模组(图中未示出)中不同长度的光纤环路传播，不同长度的光纤环路使得3个光子在光纤环路中的传播时间不同，产生了不同的时间延迟。光子离开延迟产生模组后进入光纤准直模组20，光纤准直模组20中至少包括3个目标光纤准直器21。3个光子分别进入对应的目标光纤准直器，通过光纤准直器将3个光子的光线转换成准直光。3个光子的光线之间相互平行地在自由空间中进行传播，并按照时间先后顺序进入准空间模式生成模组30。可选地，需要通过光线准直模组中的平面镜22的折射作用，改变某个光子的光线的空间位置，从而使得该光子能进入准空间模式生成模组30。3个光子在准空间模式生成模组30中分别按顺序经过传播方向上的3个镜头模组。3个光子分别通过三个镜头模组310、320和330的会聚作用，形成了空间距离很接近并且相互平行的准空间模式。3个光子分别对应的准空间模式之间的空间距离很接近，并且不会重叠。可选地，准空间模式生成模组30中还包括其它自适应光学元件如自适应平面 镜340。自适应平面镜340用于改变光子的传播方向；由于3个光子在延迟产生模组中产生的时间延迟不同，因此3个光子到达前馈测量模组40的时刻不同，前馈测量模组40利用第一光子和第二光子延迟时间之差完成对第一光子的前馈操作。在一些实施例中，在前馈测量测量模组40中第一偏振分束器42只允许处于水平偏振状态的光子通过。某个光子通过第一偏振分束器42后，继续按照原有的方向进行传播，到达有源光学元件41。可选地，有源光学元件41是电光调制器，通过改变电光调制器两极的电压，能够改变电光调制器中电光晶体的折射率，从而改变该光子的偏振状态。经过调制后的光子先后经过步长为5°的四分之一波片43以及第二偏振分束器44进行过滤。探测器45能够探测出某个光子是否到达其表面。根据探测器45的探测结果，可以确定该光子的偏振情况，生成对应于该光子的测量结果。
下面对多光子模式的有源光学前馈系统中的关键要素进行说明。
1.延迟产生模组中的光纤环路采用带有FC(Ferrule Connecter，套圈连接器)/PC(Physical Contact，物理接触)连接器的780HP光纤，这种光纤在给定波长(800nm)的损失最小，延时因子τ由前馈操作的速度确定为1/(1MHz)，在上述实施例中，三个光纤环路的长度分别为220m、440m和660m，用于量子计算的光学装置中使用的光纤类型取决于待测量的量子比特的波长，光纤环路的长度取决于前馈测量模组进行前馈操作的速度。
2.准空间模式产生模组中的至少一个镜头模组中的透镜均为镀硼紫外硅透镜材质，这种材质能够降低光子穿过透镜过程中产生的损耗，上述实施例中，各个镜头模组中透镜的参数请参考表1，准空间模式产生模组中镜头组的设计表。
表1准空间模式产生模组中镜头组的设计表
Figure PCTCN2022120888-appb-000003
3.普克尔盒：本系统采用双倍KTP晶体普克尔盒，该普克尔盒的规格为：晶体尺寸：6×6×10mm，直径：25.4mm，长度：42.2mm，CA直径：5.5mm，透光率>98％@790nm。
4.普克尔盒驱动器：本系统采用的普克尔盒驱动器规格为：工作电压2.9kV，重复率1MHz。
5.FPQA：本系统采用的FPQA的规格为：1GB 1800Mbps板载DDR3，全填充400-pin FMCH普克尔盒接口，5个Pmod端口。
下面通过3个处于高度纠缠、团簇状态的光子在上述用于量子计算的光学装置中的实验数据证明本申请的可行性。
1.关于准空间模式和光束直径的表征。
光子的光线直径和三种光子对应的准空间模式的数据由激光和DataRay产WinCamD(远红外光斑分析仪)测量得到，三个光线的直径d1、d2和d3和三个光线之间的距离D12、D23和D13(3个光子的光线分别对应的序号和3个光线之间的位置关系请参考图5中500)的相关数据，如下所示。
光子的光线直径：
d1＝(219±3)μm
d2＝(237±3)μm
d3＝(261±3)μm
光线之间的距离：
D12＝(749.52±0.71)μm
D13＝(713.81±0.71)μm
D23＝(1047.53±0.71)μm
2.关于普克尔盒对光子的光线角度变化的表征。
为了对齐普克尔盒对光子的光线施加的角度变换，请参考图5，我们再次使用激光并在前馈测量模组中使用了两个偏振分束器和一个二分之一波片，普克尔盒520之前的第一偏振分束器510用于对光子进行过滤(过滤出具有特定偏振状态的光子)，确保只有初始水平偏振光子是表征的一部分。随后，这些光子通过普克尔盒520和以5°步长旋转的二分之一波片530。第二偏振分束器540在光电二极管550之前对光子再次进行过滤(偏振)。对于每个二分之一波片530旋转到的任意一个位置，光电二极管550在普克尔盒开启和关闭时测量光子的强度，通过两个强度函数之间的相位确定了普克尔盒520设置的角度。普克尔盒520(KTP(KTiOPO 4，磷酸钛氧钾)晶体以θ＝22.5°的角度)充当二分之一波片的方式放置，并将在三个不同的光束路径中的光子从水平极化转变为对角极化。
θ1＝(22.569±0.125)°
θ2＝(22.581±0.125)°
θ3＝(22.597±0.125)°
不同角度的产生原因是由控制的二分之一波片的PCB电机的可能步长导致的。
3.关于通过普克尔盒的3个不同光束(3个光子对应的光线)角度的表征。
请参考图6，其示出光电二极管测得的强度函数与普克尔盒旋转角度的关系。
为了更清楚的理解，图6中使用虚线表示普克尔盒处于关闭状态的强度测量拟合函数，普克尔盒对所有光束的偏转相同的，普克尔盒起到角度为θ＝(22.582±0.125)°二分之一波片的作用，误差是由用于控制的二分之一波片的PCB电机的可能步长导致的。为了在图6中的区分出6中波函数，将光束1的振幅×0.7，光束2的振幅×1.3，光束3的振幅不变。
本申请一示例性实施例提供了一种量子计算系统，该系统包括上文实施例介绍的用于量子计算的光学装置。
在一些实施例中，该系统还包括，纠缠光子产生模组和测量纠错模组。
其中，纠缠光子产生模组用于产生具有n个光子的处于高度纠缠状态的光子团簇。在一些实施例中，纠缠光子产生模组中至少包括：紫外线发生器和光子产生晶体。在一些实施例中，通过紫外线发生器照射在光子产生晶体表面能产生4个处于高度纠缠状态的光子团簇。
测量纠错模组用于将上述用于量子计算的光学装置测量得到的关于光子偏振的测量结果进行纠错。在一些实施例中，某个光子的偏振信息包括空间位置中的三个分量(量子状态)。在一些实施例中，在n＝3的情况下，某个光子的偏振信息存储在其它两个光子的偏振信息的某一个分量中，通过对其它两个光子的偏振信息进行量子计算，可以判断该光子的测量结果是否出现错误，从而实现纠错过程。
下述为本申请方法实施例，方法实施例可以通过本申请提供的装置实现。对于本申请方法实施例中未披露的细节，请参照本申请装置实施例。
本申请一示例性实施例提供了一种多光子模式的有源光学前馈方法，该方法在用于量子计算的光学装置中应用，该装置包括：延迟产生模组、光纤准直模组、准空间模式产生模组和前馈测量模组，前馈测量模组中包括用于对光信号进行调制处理的有源光学元件；该方法可以包括以下几个步骤：
1.通过延迟产生模组对n个光子分别产生不同的时间延迟，以使得n个光子分别在不同的时刻到达有源光学元件，n为大于1的整数。
2.通过光纤准直模组将n个光子的光线转变成n路准直光在自由空间中传播。
3.通过准空间模式产生模组控制在自由空间中传播的n个光子的光线，依次经过同一个有源光学元件，有源光学元件用于按照n个光子到达有源光学元件的时间顺序，对n个光子的光信号依次进行调制处理。
4.通过前馈测量模组对经调制处理后的第一光子的光信号进行测量，得到第一光子的测量结果，第一光子的测量结果用于对将被测量的第二光子的测量结果进行前馈补偿或前馈纠错；其中，第一光子是n个光子中的一个光子，且第二光子是第一光子的下一个被测量的光子。
在一些实施例中，第一光子的时间延迟和第二光子的时间延迟之间的差值，与前馈操作的耗时有关。
在一些实施例中，准空间模式产生模组包括至少一个镜头模组，镜头模组使得n个光子的光线之间的空间距离减小。
在一些实施例中，镜头模组用于对n个光子的光线产生会聚作用之后再以n路准直光的形式射出。
在一些实施例中，每个镜头模组包括第一透镜和第二透镜；第一透镜用于对n个光子的光线产生会聚作用；第二透镜用于将经过第一透镜之后的n个光子的光线，转换为n路准直光的形式射出。
在一些实施例中，第一透镜为凸透镜，第二透镜为凹透镜或者凸透镜。
在一些实施例中，延迟产生模组包括n个光纤环路，n个光纤环路和n个光子一一对应；n个光纤环路用于对n个光子分别产生不同的时间延迟。
在一些实施例中，n个光纤环路具有不同的光纤长度。
在一些实施例中，光纤准直模组包括n个光纤准直器，n个光纤准直器和n个光纤环路一一对应；n个光纤准直器中的目标光纤准直器，用于将目标光纤环路中光子的光线转变成准直光在自由空间中传播；其中，目标光纤环路是n个光纤环路中与目标光纤准直器对应的光纤环路。
在一些实施例中，延迟产生模组与环境温度隔离，以便在延迟操作期间保持各个光子的偏振状态。
在一些实施例中，前馈测量模组包括：第一偏振分束器、有源光学元件、波片、第二偏振分束器、探测器和有源光学元件的驱动器；第一偏振分束器用于获得第一偏振状态的光子；有源光学元件用于改变第一偏振状态的光子的偏振状态，得到具有第二偏振状态的光子；波片和第二偏振分束器用于从第二偏振状态的光子中分离出至少一种单一偏振状态的光子；探测器用于探测至少一种单一偏振状态的光子的光强。
在一些实施例中，有源光学元件包括电光调制器。
通过延迟产生模组使得处于团簇状态相互纠缠的多个光子具有不同的时间延时；以及，通过准空间模式产生模组使得多个光子处于空间距离十分接近，但不重叠的准空间模式，使得本系统只需使用一个有源光学元件就能完成几次快速前馈操作，实现对多个光子分别进行测量，并分别获得多个光子对应的测量结果。利用多个光子的时间延迟不同，使得不同光子到达前馈测量模组的时刻不同，前馈测量模组利用相邻光子到达的时间间隔对光子进行测量得到测量结果，并基于测量结果对系统进行调整，实现前馈补偿或纠正。由于同一个前馈测量模组能够测量处于纠缠状态的多个光子之间的测量结果，因此在所测量的光子数量至少保持不变的情况下减少了计算过程中使用的有源光学元件的数量，有助于降低了量子设备的设计难度，以及降低量子设备的成本。
本申请实施例还提供一种计算机可读存储介质，该计算机可读存储介质中存储有计算机程序，计算机程序由处理器加载并执行以实现上述各方法实施例提供的多光子模式的有源光学前馈方法。
可选地，该计算机可读存储介质可以包括：ROM(Read-Only Memory，只读存储器)、RAM(Random-Access Memory，随机存储器)、SSD(Solid State Drives，固态硬盘)或光盘等。其中，随机存取记忆体可以包括ReRAM(Resistance Random Access Memory，电阻式随机存取记忆体)和DRAM(Dynamic Random Access Memory，动态随机存取存储器)。
本申请实施例还提供一种计算机程序产品，该计算机程序产品包括计算机程序，计算机程序由处理器加载并执行以实现上述各方法实施提供的多光子模式的有源光学前馈方法。
应当理解的是，在本文中提及的“多个”是指两个或两个以上。另外，本文中描述的步骤编号，仅示例性示出了步骤间的一种可能的执行先后顺序，在一些其它实施例中，上述步骤也可以不按照编号顺序来执行，如两个不同编号的步骤同时执行，或者两个不同编号的步骤按照与图示相反的顺序执行，本申请实施例对此不作限定。
以上所述仅为本申请的示例性实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (16)

  1. 一种用于量子计算的光学装置，所述装置包括：延迟产生模组、光纤准直模组、准空间模式产生模组和前馈测量模组，所述前馈测量模组中包括用于对光信号进行调制处理的有源光学元件；
    所述延迟产生模组用于对n个光子分别产生不同的时间延迟，以使得所述n个光子分别在不同的时刻到达所述有源光学元件，n为大于1的整数；
    所述光纤准直模组用于将所述n个光子的光线转变成n路准直光在自由空间中传播；
    所述准空间模式产生模组用于控制在自由空间中传播的所述n个光子的光线，依次经过同一个所述有源光学元件，所述有源光学元件用于按照所述n个光子到达所述有源光学元件的时间顺序，对所述n个光子的光信号依次进行调制处理；
    所述前馈测量模组用于对经调制处理后的第一光子的光信号进行偏振测量，得到所述第一光子的测量结果，所述第一光子的测量结果用于对将被测量的第二光子的测量结果进行前馈补偿或前馈纠错；其中，所述第一光子是所述n个光子中的一个光子，且所述第二光子是所述第一光子的下一个被测量的光子。
  2. 根据权利要求1所述的装置，其中，所述第一光子的时间延迟和所述第二光子的时间延迟之间的差值，与前馈操作的耗时有关。
  3. 根据权利要求1所述的装置，其中，所述准空间模式产生模组包括至少一个镜头模组，所述镜头模组用于使得所述n个光子的光线之间的空间距离减小。
  4. 根据权利要求3所述的装置，其中，所述镜头模组用于对所述n个光子的光线产生会聚作用之后再以所述n路准直光的形式射出。
  5. 根据权利要求3所述的装置，其中，每个所述镜头模组包括第一透镜和第二透镜；
    所述第一透镜用于对所述n个光子的光线产生会聚作用；
    所述第二透镜用于将经过所述第一透镜之后的所述n个光子的光线，转换为所述n路准直光的形式射出。
  6. 根据权利要求5所述的装置，其中，所述第一透镜为凸透镜，所述第二透镜为凹透镜或者凸透镜。
  7. 根据权利要求1所述的装置，其中，所述延迟产生模组包括n个光纤环路，所述n个光纤环路和所述n个光子一一对应；
    所述n个光纤环路用于对所述n个光子分别产生不同的时间延迟。
  8. 根据权利要求7所述的装置，其中，所述n个光纤环路具有不同的光纤长度。
  9. 根据权利要求7所述的装置，其中，所述光纤准直模组包括n个光纤准直器，所述n个光纤准直器和所述n个光纤环路一一对应；
    所述n个光纤准直器中的目标光纤准直器，用于将目标光纤环路中光子的光线转变成准直光在自由空间中传播；
    其中，所述目标光纤环路是所述n个光纤环路中与所述目标光纤准直器对应的光纤环路。
  10. 根据权利要求1所述的装置，其中，所述延迟产生模组与环境温度隔离，以便在延迟 操作期间保持各个所述光子的偏振状态。
  11. 根据权利要求1所述的装置，其中，所述前馈测量模组包括：第一偏振分束器、所述有源光学元件、波片、第二偏振分束器、探测器和所述有源光学元件的驱动器；
    所述第一偏振分束器用于获得第一偏振状态的光子；
    所述有源光学元件用于改变所述第一偏振状态的光子的偏振状态，得到具有第二偏振状态的光子；
    所述波片和所述第二偏振分束器用于从所述第二偏振状态的光子中分离出至少一种单一偏振状态的光子；
    所述探测器用于探测所述至少一种单一偏振状态的光子的光强。
  12. 根据权利要求1所述的装置，其中，所述有源光学元件包括电光调制器。
  13. 一种量子计算系统，所述系统包括如权利要求1至12任一项所述的用于量子计算的光学装置。
  14. 一种多光子模式的有源光学前馈方法，所述方法在用于量子计算的光学装置中应用，所述装置包括：延迟产生模组、光纤准直模组、准空间模式产生模组和前馈测量模组，所述前馈测量模组中包括用于对光信号进行调制处理的有源光学元件；
    所述方法包括：
    通过所述延迟产生模组对n个光子分别产生不同的时间延迟，以使得所述n个光子分别在不同的时刻到达所述有源光学元件，n为大于1的整数；
    通过所述光纤准直模组将所述n个光子的光线转变成n路准直光在自由空间中传播；
    通过所述准空间模式产生模组控制在自由空间中传播的所述n个光子的光线，依次经过同一个所述有源光学元件，所述有源光学元件用于按照所述n个光子到达所述有源光学元件的时间顺序，对所述n个光子的光信号依次进行调制处理；
    通过所述前馈测量模组对经调制处理后的第一光子的光信号进行偏振测量，得到所述第一光子的测量结果，所述第一光子的测量结果用于对将被测量的第二光子的测量结果进行前馈补偿或前馈纠错；其中，所述第一光子是所述n个光子中的一个光子，且所述第二光子是所述第一光子的下一个被测量的光子。
  15. 一种计算机可读存储介质，其中，所述计算机可读存储介质中存储有计算机程序，所述计算机程序由处理器加载并执行以实现如权利要求14所述的方法。
  16. 一种计算机程序产品，其中，所述计算机程序产品包括计算机程序，所述计算机程序由处理器加载并执行以实现如权利要求14所述的方法。
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