Clock generation for light quantum computer

Abstract

A system for generating a clock signal for a light quantum computing system includes a pump photon source configured to generate a plurality of pump photon pulses having a first repetition rate; a waveguide optically coupled to the pump photon source; and a photon pair source optically coupled to the first waveguide. The system also includes a photodetector optically coupled to the photon pair source and configured to generate a plurality of electrical pulses in response to detecting at least a portion of the plurality of pumped photon pulses having a first repetition rate; and a clock generator coupled to the photodetector and configured to convert the plurality of electrical pulses into a plurality of clock signals having a first repetition rate.

Description

[0001] This application is a divisional application with application number 201980096480.7, application date June 20, 2019, and invention name “Clock generation for optical quantum computers”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Application No. 16 / 362,452, filed on March 22, 2019, the entire disclosure of which is incorporated herein by reference in its entirety for all purposes. Background Art

[0004] Optical quantum computers, such as linear optical quantum computers (LOQCs), may require routing photons through complex photonic circuits that include many optical elements, such as beam splitters, phase shifters, and mirrors. Single-photon sources can be used to generate photons that serve as qubits in quantum computing.

[0005] Despite the progress made in optical quantum computers, there remains a need in the art for improved methods and systems related to clock generation. Summary of the invention

[0006] According to an embodiment of the present invention, there is provided a system for generating a clock signal for an optical quantum computing system, which is disposed inside a cryostat. The system includes a pump photon source, which is disposed outside the cryostat. The pump photon source is configured to generate a plurality of pump photon pulses having a first repetition rate. The system also includes: a waveguide, which is optically coupled to the pump photon source; and a photon pair source, which is disposed inside the cryostat and optically coupled to the first waveguide. The photon pair source is configured to receive a plurality of pump photon pulses via the waveguide, convert a first portion of each pump photon pulse in a subset of the plurality of pump photon pulses into a photon pair, output the photon pairs converted from the subset of the plurality of pump photon pulses, and output a second portion of each pump photon pulse in the plurality of pump photon pulses. The system also includes a photodetector disposed inside the cryostat and configured to receive a second portion of each of the plurality of pump photon pulses and generate a plurality of electrical pulses by converting the second portion of each of the plurality of pump photon pulses into a corresponding electrical pulse in a plurality of electrical pulses. Furthermore, the system includes a clock generator disposed inside the cryostat and electrically coupled to the photodetector. The clock generator is configured to convert the plurality of electrical pulses generated by the photodetector into a plurality of clock signals having a first repetition rate.

[0007] According to another embodiment of the present invention, a system for generating a clock signal for an optical quantum computing system is provided. The system includes: a pump photon source configured to generate a plurality of pump photon pulses having a first repetition rate; a waveguide optically coupled to the pump photon source; and a photon pair source optically coupled to the first waveguide. The system also includes: a photodetector optically coupled to the photon pair source and configured to generate a plurality of electrical pulses in response to detecting at least a portion of the plurality of pump photon pulses having a first repetition rate; and a clock generator coupled to the photodetector and configured to convert the plurality of electrical pulses into a plurality of clock signals having a first repetition rate. In an embodiment, the first waveguide outputs a second portion of each of the plurality of pump photon pulses, and the photodetector optically coupled to the first waveguide.

[0008] According to an alternative embodiment of the present invention, a method for generating a clock signal for an optical quantum computing system is provided, the optical quantum computing system being disposed inside a cryostat. The method includes: generating a plurality of pump photon pulses having a first repetition rate using a pump photon source disposed outside the cryostat; and converting a first portion of each pump photon pulse in a subset of the plurality of pump photon pulses into a photon pair using a photon pair source disposed inside the cryostat and optically coupled to the pump photon source via a waveguide. The photon pair source outputs a second portion of each pump photon pulse in the plurality of pump photon pulses. The method also includes: generating a plurality of electrical pulses by converting a second portion of each pump photon pulse in the plurality of pump photon pulses into a corresponding electrical pulse in a plurality of electrical pulses using a photodetector disposed inside the cryostat; and generating a plurality of clock signals having a first repetition rate using the plurality of electrical pulses using a clock generator disposed inside the cryostat and coupled to the photodetector.

[0009] In an embodiment, a photon pair source, a photodetector, a clock generator, and an optical quantum computing system are disposed on a single chip placed inside a cryostat. The photon pair may include a signal photon and a marker photon. One of the signal photon or the marker photon is used as a qubit by the quantum computing system. In an exemplary embodiment, a first portion of each pump photon pulse in a subset of a plurality of pump photon pulses is non-deterministically converted into a photon pair.

[0010] In an embodiment, a source of photon pairs comprises: a first waveguide optically coupled to a pump photon source via the waveguide for receiving a plurality of pump photon pulses; a resonator optically coupled to the first waveguide and comprising a nonlinear optical material; and a second waveguide optically coupled to the resonator. The resonator may comprise one or more ring resonators. In this embodiment, the method further comprises: coupling a portion of each of the plurality of pump photon pulses from the first waveguide into the resonator. A first portion of each of the subset of the plurality of pump photon pulses that is converted into a photon pair is within the portion and is converted by the nonlinear optical material of the resonator. The method further comprises: coupling the photon pairs converted by the resonator from the subset of the plurality of pump photon pulses into the second waveguide.

[0011] In another embodiment, a second portion of each of the plurality of pump photon pulses is within the portion, and the method further comprises: coupling the second portion of each of the plurality of pump photon pulses from the resonator into the second waveguide. In some embodiments, the method further comprises: separating the second portion of each of the plurality of pump photon pulses from the photon pairs using a pump repeller disposed within the cryostat and optically coupled to the second waveguide; and coupling the second portion of each of the plurality of pump photon pulses into a photodetector for conversion into a plurality of electrical pulses. As an example, the pump repeller may comprise a spectral filter.

[0012] In yet another embodiment, the second portion of each of the plurality of pump photon pulses is within a remaining portion of each of the plurality of pump photon pulses that is not coupled into the resonator. In this embodiment, the method further comprises: coupling the second portion of each of the plurality of pump photon pulses from the first waveguide into the photodetector for conversion into a plurality of electrical pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A A hybrid computing system is shown in accordance with one or more embodiments.

[0014] Figure 1B A block diagram of a hybrid QC (quantum computing) system 101 is shown in accordance with some embodiments.

[0015] Figure 2 is a simplified block diagram of an example of a single photon source that may include a set of cascaded marker photon sources (HPS) according to some embodiments.

[0016] Figure 3 An example of a photon pair source in accordance with some embodiments is illustrated.

[0017] Figure 4An example of a single photon source comprising several multiplexed HPSs according to some embodiments is illustrated.

[0018] Figure 5A Schematically illustrates the arrival according to some embodiments Figure 4 The pump photon pulse train of the HPS is shown.

[0019] Figure 5B Illustrated Figure 4 Illustrated non-deterministic way of generating single photons by HPS.

[0020] Figure 6 A schematic block diagram of a system for generating a clock signal for an optical quantum computer according to some embodiments is illustrated.

[0021] Figure 7 is a schematic block diagram of a system for generating a clock signal for an optical quantum computer according to some other embodiments.

[0022] Figure 8 is a schematic block diagram of an alternative system for generating a clock signal for use by a single photon detector in accordance with some embodiments.

[0023] Fig. 9 is a schematic block diagram of an alternative system for generating a clock signal for use by a single photon detector according to further embodiments.

[0024] Fig.10 A simplified flow chart illustrating a method for generating a clock signal for an optical quantum computing system according to some embodiments is shown.

[0025] Fig.11 is a cross-sectional view of a package including a photonic integrated circuit and an electronic integrated circuit according to some embodiments.

[0026] Fig. 12A is a simplified schematic diagram illustrating a system including a clock signal generator according to an embodiment of the present invention.

[0027] Fig. 12B is an example of Fig. 12A A set of graphs of optical and electrical signals associated with various elements of an exemplary system.

[0028] Fig.13 is a simplified schematic diagram illustrating the generation of a clock signal in conjunction with two or more photon pair sources. DETAILED DESCRIPTION

[0029] In some optical quantum computers, various optical elements may be far away from each other, but need to operate with very precise timing. In order to achieve precise timing control, an accurate system clock may be required. Therefore, embodiments of the present invention provide systems and methods for generating clock signals for optical quantum computing systems.

[0030] Optical quantum computers (such as the following Figure 1A to Figure 1B The system shown in Figure 1 may require an accurate system clock to control the timing of the operation of various optical elements. The system clock may need to have some characteristics (such as low phase noise, small drift, etc.) in order to achieve high performance of the optical quantum computer. The system clock can be set according to the photon generation rate of the single photon source. Although it may be desirable to recover the system clock from the photon stream in a manner similar to the traditional way of recovering the clock from the data stream, this option is not feasible for optical quantum computers because doing so would require measuring and thus destroying the same photons (i.e., optical quantum bits) used to perform quantum computations. Therefore, generating an accurate clock for an optical quantum computer will be particularly challenging.

[0031] Figure 1A 1 shows a hybrid computing system according to one or more embodiments. The hybrid computing system 101 includes a user interface device 104, which is communicatively coupled to a hybrid quantum computing (QC) subsystem 106, which is described below. Figure 1B. The user interface device 104 may be any type of user interface device, such as a terminal including a display, keyboard, mouse, touch screen, etc. In addition, the user interface device itself may be a computer, such as a personal computer (PC), a laptop computer, a tablet computer, etc. In some embodiments, the user interface device 104 provides an interface that a user may use to interact with the hybrid QC subsystem 106. For example, the user interface device 104 may run software, such as a text editor, an interactive development environment (IDE), a command prompt, a graphical user interface, etc., so that a user may program the QC subsystem or otherwise interact with the QC subsystem to run one or more quantum algorithms. In other embodiments, the hybrid QC subsystem 106 may be pre-programmed, and the user interface device 104 may simply be an interface at which a user may initiate quantum computations, monitor progress, and receive results from the hybrid QC subsystem 106. The hybrid QC subsystem 106 also includes a conventional computing system 108, which is coupled to one or more quantum computing chips 110. In some examples, the conventional computing system 108 and the quantum computing chip 110 may be coupled to other electronic and / or optical components 112, such as pulsed pump lasers, microwave oscillators, power supplies, networking hardware, etc. In some embodiments where cryogenic operation is required, the quantum computing chip 110 may be housed in a cryostat (e.g., cryostat 114). In other embodiments where cryogenic operation is not required, the quantum computing chip 110, cryostat 114 may be replaced with any other housing. In some embodiments, the quantum computing chip 110 may include one or more constituent chips, such as hybrid control electronics 116 and integrated photonics 118 chips. Signals may be routed on and off the chip in any number of ways, such as via optical interconnects 120 and via other electronic interconnects 122. In addition, the hybrid computing system 101 may employ quantum computing processes, such as measurement-based quantum computing (MBQC), circuit-based quantum computing (CBQC), or any other quantum computing scheme.

[0032] Figure 1B A block diagram of a hybrid QC (quantum computing) system 101 according to some embodiments is shown. The system can be used with the above reference Figure 1A The hybrid computing system 101 is described in conjunction with FIG. Figure 1B, the solid lines represent quantum information channels and the dashed lines represent traditional information channels. Hybrid QC system 101 includes a qubit entanglement system 103, a qubit readout system 105, and a traditional computing system 107. In some embodiments, qubit entanglement system 103 takes as input a set of N physical qubits, such as physical qubits 109 (also schematically represented as inputs 111a, 111b, 111c...111n), and generates quantum entanglement between two or more of the qubits to generate an entangled state 115. For example, in the case of optical qubits, qubit entanglement system 103 can be a linear optical system (e.g., an integrated photonic circuit) that includes waveguides, beam splitters, photon detectors, delay lines, etc. In some examples, entangled state 115 can be a lattice state, cluster state, or graph state created during the course of several clock cycles of a quantum computer, or part of a larger lattice state, cluster state, or graph state. In some embodiments, the input qubit 109 can be a collection of quantum systems and / or particles, and can be formed using any qubit architecture. For example, a quantum system can be a particle, such as an atom, an ion, a nucleus, and / or a photon. In other examples, the quantum system can be other engineered quantum systems, such as flux qubits, phase qubits, or charge qubits (e.g., formed by a superconducting Josephson junction), topological qubits (e.g., Majorana fermions), or spin qubits formed by vacancy centers (e.g., nitrogen vacancies in diamond). In addition, for clarity of description, the term "qubit" is used herein, but the system can also use quantum information carriers that encode information in a manner that is not necessarily associated with a binary bit. For example, a multi-level qubit (qudit) can be used, that is, a quantum system that can encode information in more than two quantum states according to some embodiments.

[0033] According to some embodiments, hybrid QC system 101 may be a quantum computer based on quantum circuits, a measurement-based quantum computer, or any other type of quantum computer. In some embodiments, a software program (e.g., a set of machine-readable instructions) may be delivered to a conventional computing system 107 (e.g., corresponding to the above Figure 1A108 in the hybrid QC system 101), the software program represents the quantum algorithm to be run on the hybrid QC system 101. The traditional computing system 107 can be any type of computing device (e.g., a PC, one or more blade servers, etc.), or even a high-performance computing system, such as a supercomputer, a server farm, etc. Such a system may include one or more processors (not shown) coupled to one or more computer memories (e.g., memory 106). Such a computing system will be referred to as a "traditional computer" in this article. In some examples, the software program can be received by a traditional computing module, which is referred to as a detection pattern generator 113 in this article. One function of the detection pattern generator 113 is to generate a set of machine-level instructions from an input software program (which can be generated as a code that can be more easily written by a user to program a quantum computer), that is, the detection pattern generator 113 can operate as a compiler, a logical processor and / or an encoder to allow the software program to run on a quantum computer. The detection pattern generator 113 can be implemented as pure hardware, pure software, or any combination of one or more hardware or software components or modules. In some examples, the compiled machine-level instructions take the form of one or more data frames that instruct the qubit readout circuit to perform one or more quantum measurements on the entangled state 115. A measurement pattern 117 (e.g., a data frame) is an example of a set of measurements and / or gates that should be applied to the qubits of the entangled state 115 during a certain clock cycle when executing the program. In other examples, for example, the measurement pattern 117 may include instructions for applying multi-qubit measurements and / or multi-qubit gates, for example, when it is desired to apply a fusion gate to two or more qubits or when performing a stable sub-measurement. In some embodiments, several measurement patterns 117 may be stored in the memory 106 as conventional data. In general, the measurement pattern 117 may indicate whether the detectors of the qubit detection array 121 from the qubit readout circuit 105 should measure a given qubit that constitutes the entangled state 115. In addition, the measurement pattern 117 may also store the basis (e.g., Pauli X, Y, Z, etc.) on which the measurement should be performed in order to execute the program. In some examples, measurement mode 117 may also include a set of gates that should be applied by the qubit entanglement circuit to the next set of physical qubits 109 that will be processed at some future clock cycle of hybrid QC system 101 .

[0034] The controller circuit 119 of the qubit readout circuit 105 may receive data encoding the measurement pattern 117 and generate configuration signals necessary to drive a set of detectors within the qubit detection array 121. The detector may be any detector that can detect the quantum state of one or more qubits in an entangled state 115. For example, in the case of optical qubits, the detector may be a single photon detector coupled to one or more waveguides, beam splitters, interferometers, switches, polarizers, polarization rotators, etc. One of ordinary skill in the art will appreciate that many types of detectors may be used depending on the particular qubit architecture.

[0035] In some embodiments, the result of applying detection pattern 117 to the qubit detection array is a readout operation that "reads out" the quantum state of the qubits in entangled state 115. Once this measurement is completed, the quantum information stored in entangled state 115 is converted into conventional information corresponding to a set of characteristic values ​​measured by the detector, referred to herein as "measurements." These measurements can be stored in a measurement data frame (e.g., data frame 122) and communicated back to a conventional computing system for further processing.

[0036] In some embodiments, any sub-module in the hybrid QC system 101 (e.g., controller 123, quantum gate array 125, detection array 121, controller 119, detection pattern generator 113, decoder 133, and logic processor 108) may include any number of conventional computing components, such as processors (CPU (central processing unit), GPU (graphics processing unit), TPU (task processing unit)), memory (any form of RAM (random access memory), ROM (read-only memory)), hard-coded logic components (conventional logic gates, such as AND, OR, XOR, etc.) and / or programmable logic components (e.g., field programmable gate array (FPGA, etc.). These modules may also include any number of application specific integrated circuits (ASICs), microcontrollers (MCUs (microprogrammed controllers)), systems on a chip (SOCs), and other similar microelectronic devices.

[0037] As described herein, logical qubit measurement results 127 can be recovered from physical qubit measurement results 122 in a fault-tolerant manner (e.g., via decoder 133). In the case of a cluster state that is also a stable substate, the decoder uses error syndromes generated by the measurement of a joint parity measurement (formed by a combination of one or more stable submeasurements) to identify and correct errors so that the correct logical qubit measurement results can be determined. The logic processor 108 can then process the logic results as part of the program execution. As shown, the logic processor 108 can feed information back to the detection pattern generator 113 to affect downstream gates and / or measurements to ensure that the calculation is performed fault-tolerantly.

[0038] According to some embodiments, it may be beneficial to synchronize or otherwise temporally coordinate the actions of any or all components of a hybrid QC system. Advantageously, one or more embodiments provide systems and methods for generating and distributing clock signals using residual light (i.e., photons) from a pulse train originating from a pump laser, such as housed in a Figure 1A Within the electronic and / or optical assembly 112 as shown.

[0039] In the following description, an embodiment using the spatial mode of photons as a qubit system is described, but one of ordinary skill in the art will understand that any type of qubit described by any type of mode may be employed without departing from the scope of the invention. In addition, in the following, a photonic waveguide is used to define the spatial mode of a photon. However, one of ordinary skill in the art who benefits from the present invention will understand that any type of mode (e.g., polarization mode, time mode, etc.) may be used without departing from the scope of the invention. The figures shown in the remaining figures are schematic diagrams in which each horizontal line represents a mode of a quantum system, such as a waveguide.

[0040] Figure 2 is a simplified block diagram of an example of a single photon source 200 that may include a set of cascaded heralded photon sources (HPS) according to some embodiments. Figure 2In the example shown, the single photon source 200 may include multiple HPS205a, 205b, etc., which may be collectively referred to as HPS205. Each HPS205 may include a photon pair source, such as a photon pair source 210a in HPS205a or a photon pair source 210b in HPS205b. Each photon pair source 210a or 210b may generate photon pairs based on, for example, spontaneous four wave mixing (SFWM) in a third-order passive nonlinear optical material or spontaneous parametric down-conversion (SPDC) in a second-order passive nonlinear optical material. In some implementations, the photon pair source 210a or 210b may include a ring resonator that may support multiple resonances, as described below.

[0041] It should be understood that although some embodiments are described with respect to photon pair sources, this is not required and photon sources other than photon pair sources are also included within the scope of the present invention. Therefore, for illustration, a microring-based SPFW labeled photon source (HPS) is described as an example of a photon source. However, the precise type of photon source used is not necessary, and any type of nonlinear source can be used, which employs any process, such as SPFW, spontaneous parametric down conversion (SPDC) or any other process. Other types of sources that do not necessarily require nonlinear materials can also be used, for example, sources using atoms and / or artificial atomic systems, such as quantum dot sources, color centers in crystals, etc. can be used.

[0042] In some cases, the source may be or may be coupled to a photonic cavity, for example as may be the case for artificial atom systems such as quantum dots coupled to a cavity.SPWM and SPDC There are other types of photonic sources such as optomechanical systems and the like.

[0043] For illustration, an example of spatial multiplexing with several non-deterministic schemes is described as an example of a multiplexed (MUX) photon source. However, without departing from the scope of the present invention, many different spatial MUX architectures are possible. Temporal MUX can also be implemented in place of spatial multiplexing or in combination with spatial multiplexing. MUX schemes using logarithmic trees, generalized Mach-Zehnder interferometers, multimode interferometers, linked sources, linked sources with dump pumping schemes, asymmetric polycrystalline single photon sources, or any other type of MUX architecture can be used. In some embodiments, the photon source can use a MUX scheme with quantum feedback control, etc.

[0044] In each photon pair source 210a or 210b, the photons may be generated in pairs non-deterministically, wherein each pair includes a signal photon and an idler photon, and the presence of one photon (e.g., an idler photon) may indicate the presence of the other photon (e.g., a signal photon) in the pair. The two photons in each pair may be separated into two output channels by a splitter (e.g., a wavelength division demultiplexing (WDDM) device 220a or 220b) based on their different frequencies. One photon (e.g., an idler photon) on one output channel of the splitter (e.g., a WDDM device 220a or 220b) may be detected by a single photon detector (SPD) 230a or 230b. If SPD 230a or 230b detects a photon, the corresponding photon (e.g., signal photon) generated in the same pair as the detected photon will be present on a different output channel of splitter 220a or 220b and can therefore be used as the output of single photon source 200. When SPD 230a or 230b in one of the cascaded HPSs 205a and 205b detects an idler photon, SPD 230a or 230b can send an electrical signal (referred to herein as a marker signal) to the other HPS so that these HPSs can be disconnected or bypassed. For example, in Figure 2 In the example shown, if the SPD 230a in the first HPS 205a detects a photon, the SPD 230a can send a flag signal to the second HPS 205b so that the second HPS 205b can be shut down or bypassed. The signal photon generated by the first HPS 205a can pass through the second HPS 205b as the output of the single photon source 200.

[0045] Figure 3 An example of a photon pair source 300 according to some embodiments is illustrated. The photon pair source 300 may include a first waveguide 310, a second waveguide 330, and a ring resonator 320 positioned between the first waveguide 310 and the second waveguide 330. Pump light (e.g., generated by a laser source) may propagate in the first waveguide 310 (as indicated by the arrows) and may be coupled into the ring resonator 320. The ring resonator 320 may include a waveguide loop so that when the optical path length of the ring resonator 320 is an integer multiple of the wavelength of the light, resonance of light having a specific wavelength may occur. The ring resonator 320 may support multiple resonances at multiple wavelengths that may satisfy the resonance condition. The spacing between these resonances may be referred to as a free spectral range (FSR) and may depend on the optical path length of the ring resonator 320.

[0046] The ring resonator 320 may include a nonlinear optical material, such as a second-order or third-order passive nonlinear optical medium. A spontaneous four-wave mixing (SFWM) or spontaneous parametric down conversion (SPDC) process may occur in the ring resonator 320. In the SFWM process, two pump photons may be converted into a pair of daughter photons (e.g., a signal photon and an idler photon) in the nonlinear optical material. Due to energy conservation, the signal photon and the idler photon may be at frequencies symmetrically distributed around the pump frequency (e.g., one at a frequency f0+Δf and the other at a frequency f0-Δf, where f0 is the frequency of the pump photon).

[0047] The signal photons and idler photons generated in the ring resonator 320 can be coupled out of the ring resonator 320 into the second waveguide 330 at a specific coupling efficiency. The propagation directions of the photons in the first waveguide 310, the ring resonator 320, and the second waveguide 330 can be as follows: Figure 3 In addition to the photon pairs generated by the resonator 320 , a certain amount of unconverted pump photons can also be coupled from the ring resonator 320 into the second waveguide 330 .

[0048] The photon pair source 300 may generate photon pairs in a non-deterministic manner. That is, the photon pairs are not generated on demand, but are generated probabilistically. The success rate may be only 1%-5%. For example, a photon pair may be successfully generated only once in every 20 pump pulses. Therefore, the photon pair source 300 is used to generate a marker photon source (HPS) of single photons (e.g. Figure 2 The illustrated HPS 205a or 205b) can also generate single photons in a non-deterministic manner. According to some embodiments, multiple HPSs can be cascaded (e.g., as Figure 2 exemplified) or multiplexed to form a precisely characterized single photon source, as described below.

[0049] As an example, Figure 4 A single photon source 400 including three multiplexed HPSs 410a-410c is shown. Pump photon pulses (e.g., laser pulses) are distributed to each HPS 410a, 410b, and 410c, for example, simultaneously. The outputs of the HPSs 410a-410c are coupled to a multiplexer (MUX) 420. For illustration purposes, Figure 4 A single photon source 400 is shown comprising three HPSs, and in some embodiments the single photon source may comprise twenty or more HPSs.

[0050] Each of the HPSs 410a-410c may generate a single photon in a non-deterministic manner. For example, Figure 5A Schematically illustrated are the pump photon pulse trains arriving at the HPSs 410a, 410b, and 410c at time slots t1, t2, and t3. Figure 5BFor example, the first HPS 410a cannot generate any single photon (indicated by a cross) in the first time slot t1 and the third time slot t3, but can generate a single photon (indicated by a check symbol) in the second time slot t2. Similarly, the second HPS 410b cannot generate any single photon in the first time slot t1 and the second time slot t2, but can generate a single photon in the third time slot t3; the third HPS 410c cannot generate any single photon in the second time slot t2 and the third time slot t3, but can generate a single photon in the first time slot t1.

[0051] When an idler photon is detected in HPS 410a, 410b, or 410c (e.g., by a single-photon detector), HPS 410a, 410b, or 410c may send a flag signal to multiplexer 420. Multiplexer 420 may be configured to select the single-photon output of one of HPSs 410a, 410b, and 410c as its single-photon output and ignore the single-photon outputs of all other HPSs. When there are a sufficient number of HPSs, single-photon source 400 is capable of generating single photons for each pump photon pulse in an accurate and qualitative manner. For example, in Figure 4 and FIG. 5A to FIG. 5B In the illustrated example, the multiplexer 420 can select the single photon output of the third HPS 410c in the first time slot t1, the single photon output of the first HPS 410a in the second time slot t2, and the single photon output of the second HPS 410b in the third time slot t3, so that the single photon source 400 outputs a single photon for each pump photon pulse in time slots t1, t2 and t3.

[0052] A shared or master clock signal may be beneficial in order for the system to deterministically sequence multiple operations of various components, including, for example, one or more single photon sources (e.g., 400a, 400b, 400c), one or more MUXs (e.g., MUX 420), and / or any other downstream components (e.g., Figure 1A to Figure 1B Thus, in some embodiments, the clock signal generator 450 can convert a portion of the pump photon pulse into a clock signal, which can then be distributed to the various components to provide the desired coordination between the components. Figure 4 The portion of the clock signal shown is derived from the output of a single photon source, but this portion may be provided from any number of different upstream or combined blocks without departing from the scope of the invention.

[0053] Reference again Figure 1B, the physical qubit inputs 111a, 111b, 111c...111n can be single photons generated by an upstream single photon source (not shown) and can be coupled to the qubit entanglement system 103, which in this example can be, for example, a complex linear optical circuit (e.g., a linear optical circuit in which up to a million qubits can exist). For example, a linear optical quantum circuit can include optical components (e.g., switches, beam splitters, phase shifters, photon detectors) that need to be coordinated in order to entangle two or more single photons or two or more entangled cluster states of photons. The linear optical quantum circuit can include quantum gates (e.g., fusion gates) at various locations to perform quantum computations. The qubit readout system 105 can include many single photon measurement circuits, and can also include many photon fusion circuits (e.g., type I and / or type II fusion gates) that can measure photons to obtain the results of quantum computations. In some architectures, the quantum gate itself can be formed / defined by a series of measurements and / or fusion operations to be performed on individual photons. In either case, there are multiple operations within the quantum computer that may require precise timing. Therefore, a precise system clock may be required to act as a "master conductor" to control the timing of the various operations of the quantum computer 101.

[0054] In some embodiments, the system clock can be set by the photon generation rate of the single photon source. The single photon source can be driven by a high-power pump laser that generates a pump photon pulse train with a specific repetition rate (e.g., a square wave pulse with a 100ps interval, which corresponds to a repetition rate of about 10GHz). The high-power pump laser can be driven by an electrical signal with a similar repetition rate. Therefore, one option for generating a clock signal is to tap some of the electrical signals that generate the pump photon pulses and deliver them to the linear optical quantum computer 101 to be used as a master clock. Unfortunately, this option may not work for one or more of the reasons discussed below.

[0055] As described above, many components of the linear optical quantum computer 101 can be implemented on a chip that is placed in a cryostat to keep these components at cryogenic temperatures to achieve high performance. On the other hand, the circuit driving the pump photon source (e.g., a power laser source) may be located away from the chip and may be at room temperature. It can be seen that there may be electrical and optical interconnections between the pump photon source and the linear optical quantum computer 101 that are subjected to very different temperature environments (e.g., from room temperature of about 293K to about 4K in a cryostat). Therefore, the master clock generated in this way may have a random phase error. Since the linear optical quantum computer requires strict timing tolerances, the phase error may cause, for example, the master clock to be unsuitable for use in the linear optical quantum computer.

[0056] Another way to generate a clock signal is to generate a clock signal from a marker signal when an idle photon is detected in a marker photon source (HPS). However, this approach may not work either. As mentioned above, the HPS can generate single photons in a non-deterministic manner. The success rate may be only 1%-5% (e.g., only one single photon is generated for every 20 pump photon pulses). Therefore, the marker signal rate may be much slower than the pump pulse rate. The slow rate and non-deterministic nature of the marker signals make them unsuitable for recovering a clock signal from them.

[0057] Embodiments of the present invention provide a method for generating a clock signal for an optical quantum computer, which utilizes an extra pump photon repelled by a single photon source that generates a single photon qubit for the optical quantum computer. The extra pump photon will usually be wasted and discharged from the system. By generating the clock signal locally on the chip where the optical quantum computer is located, random phase errors can be prevented or reduced, wherein the chip is usually placed in a cryostat.

[0058] Figure 6 A schematic block diagram of a system for generating a clock signal for an optical quantum computer according to some embodiments is illustrated. The system may include a pump photon source 602 and a photon pair source 610. The pump photon source 602 may be configured to generate a pump photon pulse train and coupled to the photon pair source 610 via a waveguide 604 (e.g., an optical fiber). The pump photon pulse train may have a repetition rate of, for example, 10 GHz.

[0059] Photon pair source 610 may be located on a chip placed inside a cryostat (eg, at cryogenic temperature). Pump photon source 602 may be at room temperature and remote from the chip. Waveguide 604 may be configured to have a specific length in order to induce a desired time delay in the optical pulse train.

[0060] According to some embodiments, the photon pair source 610 may be similar to Figure 3Example photon pair source 300. For example, the photon pair source 610 may include a first waveguide 614, a second waveguide 616, and a resonator 612 (e.g., one or more ring resonators). Pump photons are coupled into the first waveguide 614, some of which are coupled into the resonator 612. The resonator 612 may include a nonlinear optical material that can convert two pump photons into a pair of photons, one of which is a signal photon (S) and the other is an idler photon or a marker photon (H). Most of the pump photons coupled into the ring resonator 612 may be unconverted and are referred to herein as additional pump photons. The converted signal photon and marker photon pairs and additional pump photons may be coupled into the second waveguide 616 and output from the photon pair source 610. In addition, a portion of the pump photons coupled into the first waveguide 614 may not be coupled into the ring resonator 612. These pump photons are referred to herein as uncoupled pump photons. The uncoupled pump photons may be absorbed by a beam dump (not shown).

[0061] As follows about Figure 7 In addition to the discussion Figure 6 In addition to the illustrated clock generation architecture, alternative embodiments utilize all or part of the uncoupled pump photons during the clock generation process. Moreover, combinations in which coupled pump photons are utilized in addition to or instead of uncoupled pump photons are also included within the scope of the present invention. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0062] The system may also include a pump rejecter 620 coupled to the output of the photon pair source 610. The pump rejecter 620 may be configured to separate additional pump photons from the converted signal photon and idler photon pairs. Since the signal photons and the idler photons may have frequencies different from the frequencies of the additional pump photons, the pump rejecter 620 may include a spectral filter configured to spectrally separate the additional pump photons from the signal photons and the idler photons. For example, assuming that the frequency of the pump photons is f0, the signal photons and the idler photons may have frequencies f0+Δf and f0-Δf, respectively. The pump rejecter 620 may include a notch filter that passes the signal photons and the idler photons at their respective frequencies and sends the pump photons at the frequency f0 along a different path. As described above, a majority of the pump photons in the pump photon pulse (e.g., approximately 10 per 10 pJ pulse) are not included in the pump photon pulse. 10 photons of the order of magnitude) may be unconverted.

[0063] Similar to Figure 2The illustrated marker photon source (HPS) 205a, the signal photon (S) and the idler photon (H) can be transmitted to a wavelength division multiplexing (WDDM) device 630, which spectrally separates the signal photon and the idler photon. The idler photon (H) can be detected by a single photon detector (SPD) 640. The single photon detector 640 can send a marker signal (electrical signal) to the multiplexer 650 when the idler photon is detected, so that the multiplexer 650 can couple the signal photon (S) to its output for use as a quantum bit for an optical quantum computer, and bypass or ignore the outputs of other HPSs coupled to the multiplexer 650 ( Figure 6 not shown).

[0064] The system may also include a photodetector 670 and a clock generator 660. The photodetector 670 is optically coupled to the pump repeller 620 for receiving additional pump photons repelled by the pump repeller 620. The photodetector 670 may convert the additional pump photons into electrical pulses. The electrical pulses are in turn input to the clock generator 660, which generates a clock signal from the electrical pulses. In some embodiments, the clock generator 660 may include a photoamplifier that amplifies the electrical pulses generated by the photodetector 670 to generate clock signals 662 and 664.

[0065] In some embodiments, the photodetector 670 can be integrated with the clock generator 660. Therefore, embodiments in which the photodetector 670 is integrated with the clock generator 660 and embodiments in which the photodetector 670 is implemented separately from the clock generator 660 (e.g., as separate components) are included within the scope of the present invention. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0066] Fig. 12A is a simplified schematic diagram illustrating a system including a clock signal generator according to an embodiment of the present invention. Fig. 12B is an example of Fig. 12A A set of graphs of optical and electrical signals associated with various elements of an exemplary system. Fig. 12A The illustrated clock signal generator 1230 may be used as any of the clock signal generators described in this application, such as clock generator 660, clock generator 760, clock generator 860, or clock generator 960. Fig. 12A As an example, the system includes a pump photon source 1210 and a photon pair source 1212, which can be respectively Figure 6 The pump photon source 602 and the photon pair source 610 are compared in FIG. Fig. 12B , the optical signal (eg, optical pulse) transmitted by the pump photon source 1210 is exemplified as Fig. 12B The pump curve in .

[0067] Additional pump photons are delivered to detector 1220, which can be coupled to Figure 6 Detector 1220 converts the additional pump photons into electrical pulses. Fig. 12B , the electrical pulse output by the detector 1220 is illustrated as curve “a”, i.e., the detector current. The clock signal generator 1230 receives the electrical pulse output by the detector 1220 and includes a transimpedance amplifier (TIA) 1232 and a limiting amplifier 1234. The output of the TIA 1232 is illustrated as Fig. 12B Curve "b" in the figure is the TIA output. Therefore, the output of the limiting amplifier 1234 is Fig. 12B An exemplary clock signal "ck", ie, the limiting amplifier output, is shown. The clock signal "ck" may be considered to be a recovered electrical clock from the pump photon source and is provided to circuit 1240 as described herein.

[0068] Fig.11 is a cross-sectional view of a package including a photonic integrated circuit and an electronic integrated circuit according to some embodiments. Fig.11 , package 1100 includes a photonic integrated circuit (PIC) die 1130 (also referred to as a PIC wafer), an electronic integrated circuit (EIC) die 1140, a PCB (printed circuit board) 1120, one or more electrical connectors 1122, and an optical fiber 1150 on a silicon handle wafer 1110. Although Fig.11Only one PIC / EIC die stack is shown, but multiple PIC / EIC die stacks may be included in the package 1100. As illustrated, the PCB 1120 is attached to the silicon handle wafer 1110 using, for example, epoxy resin or by fusion bonding or hybrid bonding, depending on the material of the PCB 1120. One or more PCBs 1120 may be attached to the silicon handle wafer 1110 at different horizontal or vertical positions. The PIC / EIC die stack includes an EIC die 1140, which is bonded face-to-face with the PIC die 1130 (e.g., by fusion bonding or hybrid bonding), so that the PIC may directly face the EIC. The PIC / EIC die stack may be bonded to the silicon handle wafer 1110 by, for example, fusion bonding. The EIC die 1140 may be electrically connected to the PCB 1120 by bonding wires 1142, wherein the bonding areas and bonding wires may only be on the top and bottom sides of the PIC / EIC die stack. The left and right sides of the PIC / EIC die stack can be coupled with optical fibers, which can be attached to the PCB 1120 via a harness. The PCB 1120 may also include an electrical connector 1122 and some other electronic components, such as a voltage regulator, a power management IC (integrated circuit), decoupling capacitors, and the like.

[0069] exist Fig.11 In the illustrated cross-sectional view, the PCB 1120 and the PIC / EIC die stack are bonded to the top surface of the silicon handle wafer 1110. The PCB 1120 may include multiple layers of interconnect traces or planes connected by vias. Electronic components (e.g., electrical connectors 1122 and decoupling capacitors 1124) may be soldered on the top surface of the PCB 1120. The PCB 1120 may also include pads 1126 on the top surface of the PCB 1120.

[0070] The PIC / EIC die stack may include a PIC die 1130 and an EIC die 1140. The PIC die 1130 may include a back side 1133 bonded to the silicon handle wafer 1110. The PIC die 1130 may also include a front side 1131, which may include circuits or pads. The EIC die 1140 may include a back side 1143, which may include a redistribution layer (RDL) and a bonding area 1148. The EIC die 1140 may also include a front side 1141, which may include circuits or pads. The EIC die 1140 and the PIC die 1130 may be bonded face to face with each other, so that the front side 1131 of the PIC die 1130 and the front side 1141 of the EIC die 1140 may directly face each other, and the interconnection may be short. The PIC die 1130 may include waveguides 1132 and 1136 and a photodetector 1134. The EIC die 1140 may include a number of through-silicon vias (TSVs) 1146 and control logic 1144. The photodetector 1134 may detect single photons from the waveguide 1132 and send the detection results to the control logic 1144, which may determine whether and how to tune the waveguide 1136 (e.g., turn the optical switch on or off). The bonding area 1148 may be connected to the control logic 1144 via TSVs and may also be connected to the pads 1126 on the PCB 620 via bonding wires 1142.

[0071] Use Fig.11 illustrative packaging, some embodiments implement the clock signal generator in the PIC, while other embodiments implement the clock signal generator using components present in both the PIC and the EIC. Thus, the signal paths from the PIC to the EIC and from the EIC to the PIC can be used to provide both electrical and optical or photonic functions. Thus, Fig.11 An architecture is illustrated that enables the photodetector 670 to be integrated with the clock generator 660 in the PIC. The architecture also enables the clock generator 660 to be implemented using some components in the EIC as well as separate components (e.g., the photodetector 670) implemented in the PIC. Thus, embodiments of the present invention implement a clock signal generator in a single semiconductor package that can be disposed in a cryostat for low temperature operation. Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0072] refer to Fig.11 In one embodiment, the photodetector 1134 implemented in the PIC die 1130 is used as Figure 6The photodetector 660 in the EIC die 1140 is used as the clock generator 660. Therefore, although Fig.11 illustrates a number of components that may not be used to implement elements of a clock generator, but Fig.11 An exemplary implementation is illustrated. Additional description related to integrating a PIC die and an EIC die in a single package is provided in U.S. Provisional Patent Application No. 62 / 784,284 (Attorney Docket No. 104456-1111138-001100US), filed on December 21, 2018, the disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0073] It should be understood that the EIC and PIC can be implemented on a single substrate, or on different substrates as required by a particular application. Moreover, if implemented on different substrates, the EIC and PIC can be implemented in a single package. Therefore, embodiments of the present invention utilize component integration, such as on the same substrate or the same package, which results in improvements and system performance that cannot be obtained using free space technology. Those of ordinary skill in the art will recognize many variations, modifications and substitutions.

[0074] The clock signal can be input to the multiplexer 650, as exemplified by clock signal 662, to control the operation of the multiplexer 650 (e.g., control the timing of multiplexing). The clock signal can also be used to control other components of the optical quantum computer (e.g., the conventional computer 140, the linear optical quantum circuit 120, and the reconfigurable single photon measurement circuit 130 (e.g., Figure 1A Example)) operation.

[0075] Because the clock signal is generated from the additional pump photons, the clock signal can have the same repetition rate as the pump photon pulses (e.g., 10 GHz). As described above, the photon pair source 610 can generate photon pairs non-deterministically, and the probability of successfully generating a photon pair may be only 1%-5% (e.g., only one photon pair is generated for every 20 pump photon pulses). Therefore, if the clock signal is generated from the marker signal generated by the single photon detector 640, the clock signal will be much slower. The method of generating the clock signal as described above can prevent this problem.

[0076] refer to Figure 6 , a photon pair source 610 is used in conjunction with a clock generator 660, however, embodiments of the present invention are not limited to this particular implementation.

[0077] Fig.13is a simplified schematic diagram illustrating the generation of a clock signal by combining two or more photon pair sources. Fig.13 In the example shown, multiplexed sources are used, but these sources can be separate non-multiplexed non-deterministic sources or any combination of non-multiplexed sources and multiplexed sources. In this example, pump photon pulses (not shown) can be provided to any multiplexed source (e.g., multiplexed sources 1303a...1303n), a portion of which is used to generate corresponding clock signals 1307a...1307b at each source, for example as described above with reference to Figures 6 to 9 The clock signals are provided to a clock mediator 1305, which can generate a single master clock 1309 based on the individual clock signals. There are many ways to generate such a master clock. For example, the clock mediator can perform one or more diagnostic measurements on the individual clock signals and select a diagnostic measurement based on some criteria (e.g., Allen deviation, frequency jitter, phase relative to the photon generation time, etc.). In other embodiments, the clock mediator 1305 can obtain input clock signals and combine the input clock signals via one or more mixers or other frequency reference generation circuits. In some embodiments, the clock mediator 1305 itself can include one or more frequency references, which can be used to generate the master clock.

[0078] Figure 6 A single photon pair source is illustrated, however, it should be understood that the system may include multiple photon pair sources. Figure 6 Clock signals for individual photon pair sources are illustrated, but this is not required by the present invention, and typically one clock signal will be generated in conjunction with multiple photon pair sources. It should be noted that even if the photon pair source 610 does not generate photon pairs, a clock signal can still be generated. Thus, a clock generator can be associated with each photon pair source (where selection of the clock signal is performed), or with only one of the many photon pair sources.

[0079] According to some embodiments, the photon pair source 610, the pump repeller 620, the WDDM device 630, the single photon detector 640, the multiplexer 650, the photodetector 670, and the clock generator 660 can be located on a single chip placed inside the cryostat. The photodetector 670 can include a cryogenically compatible photodiode (e.g., a Ge photodiode). The multiplexer 650 can multiplex additional photon pair sources ( Figure 6 ), to form a pseudo-deterministic single-photon source (e.g. Figure 4 illustrative.) Because the clock signal is generated from additional pump photons from a photon pair source 610 (which is located on-chip inside the cryostat), the clock signal can be synchronized with the phase of single photons generated by such a single photon source.

[0080] In contrast, if the clock signal is directly generated from an electrical signal driving a pump photon source 602 located outside the cryostat at room temperature, the clock signal may have random phase errors and drifts caused by uncertain delays in the electrical path due to large temperature differences. Such phase errors and drifts may render the clock signal unsuitable for proper operation of an optical quantum computer with tight timing tolerances. Therefore, by locally generating a clock signal from additional pump photons from a photon pair source 610 (which is located on the same chip at cryogenic temperatures), as Figure 6 For example, undesirable phase errors and drifts may be prevented or reduced.

[0081] Figure 7 is a schematic block diagram of a system for generating a clock signal for an optical quantum computer according to some other embodiments. Figure 6 The illustrated system is similar, and the system may include a pump photon source 702 located outside the cryostat at room temperature and a photon pair source 710 located inside the cryostat. The photon pair source 710 is coupled to the pump photon source 702 via a waveguide 704.

[0082] Similar to the photon pair source 610, the photon pair source 710 may include a first waveguide 714, a resonator 712 optically coupled to the first waveguide 714, and a second waveguide 716 optically coupled to the resonator 712. A portion of the pump photons may be coupled from the first waveguide 714 into the resonator 712, while the remainder of the pump photons may exit the first waveguide 714 as uncoupled pump photons. The resonator 712 may convert some of the pump photons into signal photons and marker photon pairs. The converted photon pairs and the unconverted additional pump photons may be coupled into the second waveguide 716 as outputs.

[0083] The output of the photon pair source 710 can be coupled into a pump repeller 720. The pump repeller 720 separates the signal photons (S) and the marker photons (H) from the additional pump photons, for example, via spectral filtering. The additional pump photons can be absorbed by a beam dump (not shown). The signal photons and the marker photons are again separated by a wavelength division multiplexing (WDDM) device 730. The marker photons can be detected by a single photon detector 740, which generates an electrical marker signal. The marker signal can be used by a multiplexer 750 to multiplex the signal photons generated by multiple photon pair sources.

[0084] The system may further include a photodetector 770 coupled to the clock generator 760. Here, instead of taking as input the extra pump photons that will be repelled by the pump repeller 720, the photodetector 770 takes as input the uncoupled pump photons from the first waveguide 714 of the photon pair source 710, and generates an electrical pulse to be input into the clock generator 760. Because the photon pair source 710 is placed on a chip inside the cryostat, the clock signal thus generated may also be synchronized with the phase of the single photons generated by the single photon source, and undesirable phase errors and drifts may be prevented or reduced.

[0085] Figure 8 is a schematic block diagram of an alternative system for generating a clock signal for use by a single photon detector according to some embodiments. Figure 6 The illustrated system is similar, and can include a pump photon source 802 located outside the cryostat at room temperature and a photon pair source 810 located inside the cryostat. The photon pair source 810 is coupled to the pump photon source 802 via a waveguide 804.

[0086] Similar to the photon pair source 610, the photon pair source 810 may include a first waveguide 814, a resonator 812 optically coupled to the first waveguide 814, and a second waveguide 816 optically coupled to the resonator 812. A portion of the pump photons may be coupled from the first waveguide 814 into the resonator 812, while the remainder of the pump photons may exit the first waveguide 814 as uncoupled pump photons. The resonator 812 may convert some of the pump photons into signal photons and marker photon pairs. The converted photon pairs and the unconverted additional pump photons may be coupled into the second waveguide 816 as outputs.

[0087] The output of the photon pair source 810 can be coupled into a pump repeller 820. The pump repeller 820 separates the signal photons (S) and the marker photons (H) from the additional pump photons, for example, via spectral filtering. The additional pump photons can be absorbed by a beam dump (not shown). The signal photons and the marker photons are again separated by a wavelength division multiplexing (WDDM) device 830. The marker photons can be detected by a single photon detector 840, which generates an electrical marker signal. The marker signal can be used by a multiplexer 850 to multiplex the signal photons generated by multiple photon pair sources.

[0088] The system may also include a photodetector 870 and a clock generator 860. The photodetector 870 is optically coupled to the pump repeller 820 for receiving additional pump photons repelled by the pump repeller 820. The photodetector 870 may convert the additional pump photons into electrical pulses. The electrical pulses are in turn input to the clock generator 860, which generates a clock signal from the electrical pulses. In some embodiments, the clock generator 860 may include a photoamplifier that amplifies the electrical pulses generated by the photodetector 870 to generate a clock signal.

[0089] A clock signal can be input to the multiplexer 850 for controlling the operation of the multiplexer 850. For example, the clock signal can be used to control the timing of the multiplexing. The clock signal can also be input to the single photon detector 840 for controlling the operation of the single photon detector 840. For example, the clock signal can be used to control when the single photon detector 840 should be turned on and off. The single photon detector 840 may be susceptible to parasitic noise in the environment. For example, superconducting nanowire single photon detectors are very sensitive devices and can generate dark counts in the absence of detected photons. Therefore, it is helpful to turn on the single photon detector 840 only at time intervals where photons may be expected.

[0090] Fig. 9 is a schematic block diagram of an alternative system for generating a clock signal for use by a single photon detector according to further embodiments. Figure 8 The illustrated system is similar, and the system may include a pump photon source 902 located outside the cryostat at room temperature and a photon pair source 910 located inside the cryostat. The photon pair source 910 is coupled to the pump photon source 902 via a waveguide 904.

[0091] Similar to the photon pair source 810, the photon pair source 910 may include a first waveguide 914, a resonator 912 optically coupled to the first waveguide 914, and a second waveguide 916 optically coupled to the resonator 912. A portion of the pump photons may be coupled from the first waveguide 914 into the resonator 912, while the remainder of the pump photons may exit the first waveguide 914 as uncoupled pump photons. The resonator 912 may convert some of the pump photons into signal photons and marker photon pairs. The converted photon pairs and the unconverted additional pump photons may be coupled into the second waveguide 916 as outputs.

[0092] The output of the photon pair source 910 can be coupled into a pump repeller 920. The pump repeller 920 separates the signal photons (S) and the marker photons (H) from the additional pump photons, for example, via spectral filtering. The additional pump photons can be absorbed by a beam dump (not shown). The signal photons and the marker photons are again separated by a wavelength division multiplexing (WDDM) device 930. The marker photons can be detected by a single photon detector 940, which generates an electrical marker signal. The marker signal can be used by a multiplexer 950 to multiplex the signal photons generated by multiple photon pair sources.

[0093] The system may further include a photodetector 970 and a clock generator 960. Here, instead of taking as input the extra pump photons that will be repelled by the pump repeller 920, the photodetector 970 takes as input the uncoupled pump photons from the first waveguide 914 of the photon pair source 910, and generates an electrical pulse to be input into the clock generator 960. Because the photon pair source 910 is placed on a chip inside the cryostat, the clock signal thus generated may also be synchronized with the phase of the single photons generated by the single photon source, and undesirable phase errors and drifts may be prevented or reduced.

[0094] The clock signal can be input to the multiplexer 950 for controlling the operation of the multiplexer 950. For example, the clock signal can be used to control the timing of the multiplexing. The clock signal can also be input to the single photon detector 940 for controlling the operation of the single photon detector 940. For example, the clock signal can be used to control when the single photon detector 940 should be turned on and off.

[0095] Fig.10 A simplified flow chart illustrating a method for generating a clock signal for an optical quantum computing system according to some embodiments is shown. Fig.10 As an example, the method includes: generating a plurality of pump photon pulses having a first repetition rate using a pump photon source disposed outside a cryostat (1010); and converting a first portion of each pump photon pulse in a subset of the plurality of pump photon pulses into a photon pair using a photon pair source disposed inside the cryostat and optically coupled to the pump photon source via a waveguide (1012). The photon pair source outputs a second portion of each pump photon pulse in the plurality of pump photon pulses. The photon pair may include a signal photon and a marker photon, and one of the signal photon or the marker photon is used as a qubit by a quantum computing system. The first portion of each pump photon pulse in the subset of the plurality of pump photon pulses may be converted into a photon pair non-deterministically.

[0096] The method also includes: using a photodetector disposed inside the cryostat, generating a plurality of electrical pulses by converting a second portion of each of a plurality of pump photon pulses into a corresponding electrical pulse in a plurality of electrical pulses (1014); and using a clock generator disposed inside the cryostat and coupled to the photodetector (1016) to generate a plurality of clock signals having a first repetition rate using the plurality of electrical pulses.

[0097] In an embodiment, a photon pair source, a photodetector, a clock generator, and an optical quantum computing system are provided on a single chip placed inside a cryostat. The photon pair source may include: a first waveguide optically coupled to a pump photon source via a waveguide for receiving a plurality of pump photon pulses; a resonator optically coupled to the first waveguide and including a nonlinear optical material; and a second waveguide optically coupled to the resonator. The method may further include: coupling a portion of each of the plurality of pump photon pulses from the first waveguide into the resonator. A first portion of each of the plurality of pump photon pulses in a subset of the plurality of pump photon pulses that is converted into a photon pair is within the portion and is converted by the nonlinear optical material of the resonator. The method may further include: coupling the photon pairs converted by the resonator from a subset of the plurality of pump photon pulses into the second waveguide. As an example, the resonator may include one or more ring resonators. In a specific embodiment, a second portion of each of the plurality of pump photon pulses is within the portion, and the method further comprises: coupling the second portion of each of the plurality of pump photon pulses from the resonator into the second waveguide. In another specific embodiment, the method comprises: separating the second portion of each of the plurality of pump photon pulses from the photon pairs using a pump repeller disposed within the cryostat and optically coupled to the second waveguide; and coupling the second portion of each of the plurality of pump photon pulses into a photodetector for conversion into a plurality of electrical pulses. In one embodiment, the pump repeller comprises a spectral filter.

[0098] The second portion of each of the plurality of pump photon pulses may be among the remaining portion of each of the plurality of pump photon pulses that is not coupled into the resonator. Thus, the method may include coupling the second portion of each of the plurality of pump photon pulses from the first waveguide into the photodetector for conversion into a plurality of electrical pulses.

[0099] It should be understood that Fig.10The specific steps illustrated provide specific methods for generating clock signals for optical quantum computing systems according to some embodiments. According to alternative embodiments, other step sequences may also be performed. For example, alternative embodiments may perform steps in different orders. Moreover, each step may include multiple sub-steps that may be performed in various orders suitable for each step. In addition, additional steps may be added and some steps may be removed depending on the specific application. One of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0100] It will be appreciated by those skilled in the art that substantial variations may be made depending on the particular implementation. For example, customized hardware may be used, and / or specific elements may be implemented in hardware, software (including portable software, such as applets, etc.), or both. Further, connections to other computing devices (such as network input / output devices) may be employed.

[0101] With reference to the accompanying drawings, a component that may include a memory may include a non-transient machine-readable medium. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any storage medium that participates in providing data that enables a machine to operate in a particular manner. In the embodiments provided above, various machine-readable media may be involved in providing instructions / codes to a processor and / or one or more other devices for execution. Additionally or alternatively, a machine-readable medium may be used to store and / or carry such instructions / codes. In many implementations, a computer-readable medium is a physical and / or tangible storage medium. Such a medium may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Common forms of computer-readable media include, for example, magnetic and / or optical media, punch cards, paper tapes, any other physical media with hole patterns, RAM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), FLASH-EPROM (flash EPROM), any other storage chip or cartridge, a carrier as described below, or any other medium from which a computer can read instructions and / or codes.

[0102] The methods, systems and devices discussed herein are examples. Various embodiments may appropriately omit, replace or add various processes or components. For example, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. The various components of the accompanying drawings provided herein may be implemented in hardware and / or software. Moreover, technology is developing, so many elements are examples that do not limit the scope of the present invention to those specific examples.

[0103] It has proven convenient at times, primarily for reasons of common usage, to refer to such signals as bits, information, values, elements, symbols, characters, variables, terms, numbers, and the like. It should be understood, however, that all of these or similar terms are associated with the appropriate physical quantities and are merely convenient labels. Unless otherwise specifically stated, as will be apparent from the above discussion, it should be understood that throughout the present invention, discussions utilizing terms such as "processing," "computing," "calculating," "determining," "ascertaining," "identifying," "correlating," "measuring," "performing," and the like refer to the actions or processes of a particular apparatus, such as a special-purpose computer or similar special-purpose electronic computing device. Thus, in the context of the present invention, a special-purpose computer or similar special-purpose electronic computing device is capable of manipulating or transforming signals, which are typically represented as physical electronic, electrical, or magnetic quantities within a memory, register, or other information storage device, transmission device, or display device of the special-purpose computer or similar special-purpose electronic computing device.

[0104] Those skilled in the art will appreciate that any of a variety of different techniques and methods may be used to represent information and signals used to transmit the messages described herein. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be mentioned throughout the above description may be represented by voltage, current, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, or any combination thereof.

[0105] As used herein, the terms "and", "or" and "and / or" may include multiple meanings, which are also expected to depend at least in part on the context in which the terms are used. Generally, "or" when used in an associative list (e.g., A, B, or C) is intended to mean A, B, and C (used herein in an inclusive sense) as well as A, B, or C (used herein in an exclusive sense). In addition, the term "one or more" as used herein may be used to describe any feature, structure, or characteristic in the singular, or may be used to describe a certain combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and the subject matter claimed is not limited to this example. In addition, the term "at least one of..." when used in an associative list (e.g., A, B, or C) may be interpreted to mean any combination of A, B, and / or C, such as A, B, C, AB, AC, BC, AA, AAB, ABC, AABBCCC, etc.

[0106] References throughout this disclosure to "one example," "example," "some examples," or "exemplary implementations" mean that a particular feature, structure, or characteristic described in conjunction with a feature and / or example may be included in at least one feature and / or example of the claimed subject matter. Thus, the phrases "in one example," "example," "some examples," "in some implementations," or other similar phrases that appear in various places throughout this disclosure may not all refer to the same features, examples, and / or limitations. Furthermore, particular features, structures, or characteristics may be combined in one or more examples and / or features.

[0107] In some implementations, operation or processing may involve physical manipulation of physical quantities. Typically, although not necessarily, such quantities may take the form of electrical or magnetic signals that can be stored, transferred, combined, compared, or otherwise manipulated. Mainly for general reasons, it has been proven to be convenient sometimes to refer to such signals as bits, data, values, elements, symbols, characters, items, numbers, etc. However, it should be understood that all of these or similar terms are associated with appropriate physical quantities and are merely convenient markers. Unless otherwise specifically stated, as will be apparent from the discussion herein, it should be understood that throughout the present invention, discussions using terms such as "processing", "calculation", "calculation", "determination" refer to actions or processes of specific devices (such as special-purpose computers, special-purpose computing devices, or similar special-purpose electronic computing devices). Therefore, in the context of the present invention, special-purpose computers or similar special-purpose electronic computing devices are capable of manipulating or transforming signals, which are generally represented as physical electronic quantities or magnetic quantities in the memory, registers, or other information storage devices, transmission devices, or display devices of special-purpose computers or similar special-purpose electronic computing devices.

[0108] Many specific details have been set forth in the foregoing detailed description to provide a thorough understanding of the claimed subject matter. However, it will be appreciated by those skilled in the art that the claimed subject matter may be practiced without these specific details. In other cases, methods and apparatus that would be understood by a person of ordinary skill in the art are not described in detail to avoid obfuscating the claimed subject matter. Therefore, it is contemplated that the claimed subject matter is not limited to the specific examples disclosed, but rather that such claimed subject matter may also include all aspects that fall within the scope of the appended claims and their equivalents.

[0109] For implementations involving firmware and / or software, the methods may be implemented with modules (e.g., procedures, functions, etc.) that perform the functions described herein. Any machine-readable medium that tangibly implements instructions may be used to implement the methods described herein. For example, software code may be stored in a memory and executed by a processor unit. The memory may be implemented within or outside the processor unit. As used herein, the term "memory" refers to any type of long-term, short-term, volatile, non-volatile, or other memory, and is not limited to any particular type of memory or any particular amount of memory, or a type of medium on which memory is stored.

[0110] If implemented in firmware and / or software, the functions may be stored as one or more instructions or codes on a computer-readable storage medium. Examples include computer-readable media encoded with data structures and computer-readable media encoded with computer programs. Computer-readable media include physical computer storage media. The storage medium may be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may include RAM, ROM, EEPROM (Electrically Erasable Programmable Read-Only Memory), compact Disc Read-Only Memory (CD-ROM) or other optical disk storage, magnetic disk storage, semiconductor storage, or other storage device, or any other medium that can be used to store the desired program code in the form of instructions or data structures and can be accessed by a computer; as used herein, disks and optical disks include compact discs (CD), laser optical disks, optical optical disks, digital versatile discs (DVD), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically, while optical disks reproduce data optically using lasers. The above combinations should also be included in the scope of computer-readable media.

[0111] In addition to being stored on a computer-readable storage medium, instructions and / or data may be provided as signals on a transmission medium included in the communication device. For example, the communication device may include a transceiver having signals indicating instructions and data. The instructions and data are configured to cause one or more processors to implement the functions outlined in the claims. That is, the communication device includes a transmission medium having a signal indicating information for performing the disclosed functions. At a first time, the transmission medium included in the communication device may include a first portion of the information for performing the disclosed functions, and at a second time, the transmission medium included in the communication device may include a second portion of the information for performing the disclosed functions.

Claims

1. A system for generating a clock signal for an optical quantum computing system, the system comprising: a pump photon source configured to generate a plurality of pump photon pulses having a first repetition rate; a photon pair source, optically coupled to the pump photon source and configured to: converting a subset of the plurality of pump photon pulses into photon pairs; outputting the photon pair; as well as outputting a portion of each pump photon pulse of the plurality of pump photon pulses; a photodetector optically coupled to the pump photon source and configured to: receiving the portion of each of the plurality of pump photon pulses; and converting the portion of each of the plurality of pump photon pulses into a corresponding electrical pulse in a plurality of electrical pulses; and A clock generator is electrically coupled to the photodetector and configured to convert the plurality of electrical pulses into a plurality of clock signals having the first repetition rate.

2. The system according to claim 1, characterized in that The photon pair source, the photodetector, the clock generator, and the optical quantum computing system are disposed inside a cryostat, and the pump photon source is disposed outside the cryostat.

3. The system according to claim 1, characterized in that Each of the photon pairs includes a signal photon and a marker photon.

4. The system according to claim 3, characterized in that One of the signal photon or the marker photon is used as a quantum bit by the optical quantum computing system.

5. The system according to claim 1, characterized in that Also includes: waveguide which is optically coupled to the pump photon source.

6. A system comprising: Pump photon source; a photon pair source optically coupled to the pump photon source, wherein the photon pair source is configured to: receiving a plurality of pump photon pulses from the pump photon source; converting a first portion of the plurality of pump photon pulses into photon pairs; outputting the photon pairs; and outputting a second portion of the plurality of pump photon pulses; and A photodetector is optically coupled to the source of photon pairs and is configured to generate a plurality of electrical pulses in response to detecting at least a portion of the plurality of pump photon pulses.

7. The system according to claim 6, characterized in that Also includes: A clock generator is coupled to the photodetector and is configured to convert the plurality of electrical pulses into a plurality of clock signals for an optical quantum computing system.

8. The system according to claim 7, characterized in that The photon pair source and the photodetector are implemented in a photonic integrated circuit (PIC), and the clock generator is implemented in an electronic integrated circuit (EIC).

9. The system according to claim 8, characterized in that The PIC and the EIC are fused together.

10. The system according to claim 7, characterized in that The photon pair source, the photodetector and the clock generator are implemented on the same substrate structure.

11. The system according to claim 10, characterized in that The same substrate structure includes fused PIC and EIC.

12. The system according to claim 7, characterized in that The photon pair source, the photodetector, the clock generator, and the optical quantum computing system are provided on a single chip placed inside a cryostat.

13. The system according to claim 12, characterized in that The pump photon source is disposed outside the cryostat.

14. The system according to claim 6, characterized in that The photon pair includes a signal photon and a marker photon, and one of the signal photon or the marker photon is used as a quantum bit by a quantum computing system.

15. The system according to claim 6, characterized in that The photon pair source non-deterministically converts the first portion of the plurality of pump photon pulses into the photon pairs.

16. The system according to claim 6, characterized in that The photon pair source comprises: a first waveguide for receiving the plurality of pump photon pulses generated by the pump photon source; a resonator optically coupled to the first waveguide such that a portion of each of the plurality of pump photon pulses is coupled into the resonator, the resonator comprising a nonlinear optical material for converting the first portion of the plurality of pump photon pulses into the photon pairs; and A second waveguide is optically coupled to the resonator such that the photon pairs converted from the plurality of pump photon pulses are coupled to the second waveguide.

17. The system according to claim 16, characterized in that The resonator comprises one or more ring resonators.

18. The system according to claim 16, characterized in that The second portion of the plurality of pump photon pulses is coupled into and output by the second waveguide.

19. The system according to claim 18, characterized in that Also included is a pump repeller optically coupled to the second waveguide of the photon pair source, the pump repeller being configured to: receiving the photon pairs and the second portion of the plurality of pump photon pulses; outputting the photon pairs through a first output port; as well as The second portion of the plurality of pump photon pulses is output through a second output port optically coupled to the photodetector.

20. The system according to claim 19, characterized in that The pump repeller includes a spectral filter.

21. A system for generating a clock signal for an optical quantum computing system, the system comprising: a first pump photon source configured to generate a first plurality of first pump photon pulses having a first repetition rate; a first photon pair source optically coupled to the first pump photon source; a first photodetector optically coupled to the first source of photon pairs and configured to generate a second plurality of first electrical pulses in response to detecting at least a first portion of the first plurality of first pump photon pulses having the first repetition rate; a first clock generator electrically coupled to the first photodetector and configured to convert the second plurality of first electrical pulses into a third plurality of first clock signals having the first repetition rate; a second pump photon source configured to generate a fourth plurality of second pump light pulses having a second repetition rate; a second photon pair source optically coupled to the second pump photon source; a second photodetector optically coupled to the second source of photon pairs and configured to generate a fifth plurality of second electrical pulses in response to detecting at least a second portion of the fourth plurality of second pump photon pulses having the second repetition rate; a second clock generator electrically coupled to the second photodetector and configured to convert the fifth plurality of second electrical pulses into a sixth plurality of second clock signals having the second repetition rate; as well as A clock mediator is coupled to the first clock generator and the second clock generator and is configured to generate a plurality of master clock signals having a master repetition rate, wherein the plurality of master clock signals are generated based on the third plurality of first clock signals and the sixth plurality of second clock signals.

22. The system according to claim 21, characterized in that Also included is one or more mixers operable to combine the third plurality of first clock signals with the sixth plurality of second clock signals to generate the plurality of master clock signals.

23. The system according to claim 21, characterized in that The clock mediator includes a frequency reference generation circuit operable to combine the third plurality of first clock signals with the sixth plurality of second clock signals to generate the plurality of master clock signals.

24. The system according to claim 21, characterized in that The clock mediator includes one or more frequency references.

25. The system according to claim 21, characterized in that The first photon pair source, the second photon pair source, the first photodetector, the second photodetector, the first clock generator, the second clock generator, and the clock mediator are disposed in a package.

26. The system according to claim 21, characterized in that Also included is a cryostat, wherein the system is disposed in the cryostat.

27. The system according to claim 21, characterized in that Also included is a cryostat, wherein: The first pump photon source and the second pump photon source are disposed outside the cryostat; and The first photon pair source, the second photon pair source, the first photodetector, the second photodetector, the first clock generator, the second clock generator, and the clock mediator are disposed in the cryostat.

28. The system according to claim 21, characterized in that It also includes a single chip placed in a cryostat, wherein the first photon pair source, the second photon pair source, the first photodetector, the second photodetector, the first clock generator, the second clock generator and the clock mediator are arranged on the single chip placed in the cryostat.

29. The system according to claim 21, characterized in that Also included is a first waveguide optically coupled to the first pump photon source and a second waveguide optically coupled to the second pump photon source.

30. The system according to claim 29, characterized in that Also included is a cryostat, wherein the first waveguide and the second waveguide are disposed outside the cryostat.

31. The system according to claim 21, characterized in that The first photon pair source comprises: a first waveguide operable to receive said first plurality of first pump photon pulses generated by said first pump photon source; a first resonator optically coupled to the first waveguide and comprising a first nonlinear optical material operable to convert a third portion of each of the first plurality of first pump photon pulses into first photon pairs; and a second waveguide optically coupled to the first resonator; and The second photon pair source comprises: a third waveguide operable to receive a fourth plurality of second pump light pulses generated by said second source of pump photons; a second resonator optically coupled to the first waveguide and comprising a second nonlinear optical material operable to convert a fourth portion of each pump photon pulse in the fourth plurality of second pump photon pulses into second photon pairs; and A fourth waveguide is optically coupled to the second resonator.

32. The system according to claim 31, characterized in that The first resonator and the second resonator each include one or more ring resonators.

33. The system according to claim 31, characterized in that The first photon pair includes a signal photon and a marker photon, wherein at least one of the signal photon or the marker photon includes a quantum bit.

34. The system according to claim 31, characterized in that The second photon pair includes a signal photon and a marker photon, wherein at least one of the signal photon or the marker photon includes a quantum bit.

35. The system according to claim 21, characterized in that Also includes: a photonic integrated circuit (PIC) comprising the first photon pair source, the first photodetector, the second photon pair source, and the second photodetector; and An electronic integrated circuit (EIC) includes the first clock generator, the second clock generator, and the clock mediator.

36. A method for generating a clock signal for an optical quantum computing system, the method comprising: generating, by a first pump photon source, a first plurality of first pump photon pulses having a first repetition rate; generating, by a first photodetector, a second plurality of first electrical pulses in response to detecting at least a first portion of the first plurality of first pump photon pulses having the first repetition rate; converting, by a first clock generator, the second plurality of first electrical pulses into a third plurality of first clock signals having the first repetition rate; generating, by a second pump photon source, a fourth plurality of second pump light pulses having a second repetition rate; generating, by a second photodetector, a fifth plurality of second electrical pulses in response to detecting at least a second portion of the fourth plurality of second pump photon pulses having the second repetition rate; converting, by a second clock generator, the fifth plurality of second electrical pulses into a sixth plurality of second clock signals having the second repetition rate; as well as A plurality of master clock signals having a master repetition rate are generated by a clock mediator, wherein the plurality of master clock signals are generated based on the third plurality of first clock signals and the sixth plurality of second clock signals.

37. The method according to claim 36, characterized in that Also includes: receiving, by a first photon pair source, at least a third portion of the first plurality of first pump photon pulses from the first pump photon source; converting, by the first photon pair source, a fourth portion of the first plurality of first pump photon pulses into first photon pairs; Outputting the first photon pair from the first photon pair source; outputting, by the first photon pair source, a fifth portion of the first plurality of first pump photon pulses; receiving, by a second photon pair source, at least a sixth portion of the fourth plurality of second pump light pulses from the second pump photon source; converting, by the second photon pair source, a seventh portion of the fourth plurality of second pump photon pulses into second photon pairs; outputting the second photon pair source from the second photon pair source; as well as Eight portions of the fourth plurality of second pump photon pulses are output by the second photon pair source.

38. The method according to claim 37, characterized in that Also includes: non-deterministically converting, by the first photon pair source, a ninth portion of each of the first subset of the first plurality of first pump photon pulses into first photon pairs; as well as A tenth portion of each of the second subset of the fourth plurality of second pump photon pulses is non-deterministically converted into second photon pairs by the second photon pair source.

39. The method according to claim 36, characterized in that Also includes: One or more diagnostic measurements are performed on at least one of the third plurality of first clock signals or the sixth plurality of second clock signals.

40. The method according to claim 39, characterized in that The one or more diagnostic measurements include Allan deviation, frequency jitter, or phase relative to the time of photon generation.

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