Quantum Tomography and Photon Source Optimization

Abstract

The photon source module includes multiple photon sources, each configured to non-deterministically generate one or more unentangled or entangled photons in response to receiving a trigger signal. When two or more photon sources simultaneously generate photons in response to the trigger signal, one photon of a first photon pair is directed to a photon processing system and one photon of a second photon pair is directed to a photon analyzer. During iterative operation, the photon analyzer can analyze photons from each of the multiple photon sources to determine characteristics of each photon source and use that information to direct the highest quality photons to the photon processing system.

Description

[Technical Field]

[0001] Cross-reference to other applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 042,405, filed June 22, 2020, and U.S. Non-Provisional Patent Application No. 17 / 351,101, filed June 17, 2021, which are incorporated by reference in their entireties herein for all purposes.

[0002]

[0002] The described embodiments relate generally to quantum computing, and more particularly to photon sources and characterization of photons produced by the photon sources. [Background technology]

[0003]

[0003] Photon sources can be used in many different photon quantum technologies, where an ideal photon source would produce photons deterministically. Such photon sources can be made from multiple spatially or temporally multiplexed photon sources that are coherently combined to approach a probability of one for each photon generation "cycle." During operation of the photon source, it would be beneficial to monitor the quality of the photons produced by each individual photon source and to monitor the quality of each photon source to optimize the performance of the system. Summary of the Invention

[0004]

[0004] The summary is complete after the claims are approved.

[0005] In some embodiments, a quantum computing system includes a photon processing system, a photon analyzer, and a photon source module coupled to the photon processing system and the photon analyzer. The photon source module includes at least one photon source configured to emit one or more photons per trigger signal, and a photon multiplexer configured to direct the one or more emitted photons to the photon processing system or the photon analyzer. In various embodiments, the photon multiplexer directs the one or more emitted photons to the photon processing system when the photon source module emits one photon per trigger signal.

[0006] In some embodiments, when the photon source module emits two or more photons per trigger signal, the photon multiplexer directs one of the one or more emitted photons to the photon analyzer. In various embodiments, the photon processing system is a resource state generator. In some embodiments, the one or more photons are entangled photons. In some embodiments, the at least one photon source is a plurality of spatially multiplexed photon sources. In various embodiments, the at least one photon source is a plurality of temporally multiplexed photon sources.

[0007] In some embodiments, a quantum computing system includes a first photon source configured to generate one or more first photons, a second photon source configured to generate one or more second photons, and a photon multiplexer configured to direct one of the one or more first photons or one of the one or more second photons to a photon analyzer when the first photon source and the second photon source simultaneously generate photons. In various embodiments, the device includes a first photon source configured to generate first photon pairs, each first photon pair including a first signal photon and a first herald photon. The second photon source is configured to generate second photon pairs, each second photon pair including a second signal photon and a second herald photon. The first detector is configured to generate a first detection signal in response to detecting the first herald photons. The second detector is configured to generate a second detection signal in response to detecting the second herald photons. The detection logic circuit is configured to direct one of the first or second signal photons to a photon analyzer and direct one of the first or second signal photons to a photon processing system in response to the detection logic circuit receiving the first and second detection signals.

[0008] In some embodiments, the device further comprises a multiplexer that routes one of the first or second signal photons to a photon analyzer and routes one of the first or second signal photons to a photon processing system in response to receiving one or more signals from the detection logic. In various embodiments, the detection logic directs the first and second signal photons based on a quality level of each of the first and second signal photons. In some embodiments, in response to receiving the first or second signal photons, the photon analyzer determines one or more characteristics of the received signal photons.

[0009] In some embodiments, the one or more characteristics include color, jitter, wavelength, spectral width, or dispersion. In various embodiments, during the repeated operation of the first and second photon sources, the photon analyzer determines one or more characteristics of the first signal photons generated by the first photon source and one or more characteristics of the second signal photons generated by the second photon source.

[0010] In some embodiments, the photon analyzer compares one or more characteristics of the first signal photons to one or more characteristics of the second signal photons. In various embodiments, in response to the comparison, the photon analyzer transmits instructions to the photon processing system to receive more of the first signal photons than the second signal photons. In some embodiments, the device further comprises a crossover switch that redirects signal photons routed by the multiplexer to the photon analyzer to the photon processing system.

[0011] In some embodiments, a method of generating photons includes generating a first photon pair using a first photon source, the first photon pair including a first signal photon and a first herald photon; generating a second photon pair using a second photon source, the second photon pair including a second signal photon and a second herald photon; generating a first detection signal in response to detecting the first herald photon and a second detection signal in response to detecting the second herald photon; one of the first or second signal photons is sent to a photon analyzer, and one of the first or second signal photons is routed to a photon processing system in response to detection logic receiving the first and second detection signals.

[0012] In some embodiments, the routing is performed by a multiplexer controlled by the detection logic. In various embodiments, the detection logic instructs the multiplexer to route the first and second signal photons based on a quality level of each of the first and second signal photons. In some embodiments, in response to receiving the first or second signal photons, the photon analyzer determines one or more characteristics of the received signal photons. In various embodiments, the one or more characteristics include color, jitter, wavelength, spectral width, or dispersion. In some embodiments, during repeated operation of the first and second photon sources, the photon analyzer determines one or more characteristics of the first signal photons and one or more characteristics of the second signal photons. In various embodiments, in response to determining the one or more characteristics of the first and second signal photons, the photon analyzer sends instructions to the photon processing system to receive more first signal photons than second signal photons.

[0013] In some embodiments, the photon source comprises a plurality of photon sources each configured to non-deterministically generate photon pairs in response to receiving a trigger signal, each photon pair including a signal photon and a herald photon. The plurality of photon detectors are each coupled to a respective photon source of the plurality of photon sources and configured to generate a respective detection signal upon detecting a herald photon of each generated photon pair. The plurality of photon routing switches are each coupled to a respective photon source and configured to direct a respective signal photon to a photon processing system or a photon analyzer. The photon detection logic receives each respective detection signal and is configured to send control signals to the plurality of photon routing switches in response to receiving two or more detection signals per trigger signal to route one signal photon to the photon analyzer and one signal photon to the photon processing system.

[0014] In some embodiments, in response to receiving a signal photon, the photon analyzer determines one or more characteristics of the signal photon. In various embodiments, after receiving multiple trigger signals, the photon analyzer determines one or more characteristics of the signal photon generated by each of the multiple photon sources and ranks the quality of each of the photon sources. In some embodiments, in response to receiving two or more detection signals per trigger signal, the photon analyzer transmits two or more signals that cause signal photons from the highest quality photon source to be routed to the photon processing system.

[0015]

[0015] For a better understanding of the nature and advantages of the present disclosure, reference should be made to the following description and accompanying drawings. It should be understood, however, that each figure is provided for illustrative purposes only and is not intended as a definition of the limits of the scope of the present disclosure. Furthermore, as a general rule, unless otherwise apparent from the description in which elements in different figures use the same reference numerals, the elements are generally identical or at least similar in function or purpose. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a simplified schematic diagram of a qubit entanglement subsystem according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a simplified schematic diagram of a qubit entanglement subsystem including a spatially multiplexed photon source, according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a simplified schematic diagram of a qubit entanglement subsystem including a spatially multiplexed photon source, according to an embodiment of the present disclosure. [Figure 4] FIG. 1 illustrates a method for generating photons and analyzing excess photons for a photon processing system according to an embodiment of the present disclosure. [Figure 5] 1 is a method for generating and controlling signal photon quality for a photon processing system according to some embodiments of the present disclosure. [Figure 6]FIG. 1 is a simplified schematic diagram of a qubit entanglement subsystem including a temporally multiplexed photon source, according to an embodiment of the present disclosure. [Figure 7] FIG. 1 is a simplified block diagram of an example linear optical quantum computer, according to embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0017]

[0023] The techniques disclosed herein generally relate to quantum computing applications. More specifically, the techniques disclosed herein relate to a photon source including multiple spatially or temporally multiplexed non-deterministic photon sources that direct photons to both a photon processing system and a photon analyzer. Results from the photon analyzer can be used to characterize the photons generated by each of the multiple photon sources and direct the highest quality photons to the photon processing system. In additional embodiments, the photon analyzer can be used to ascertain entanglement state parameters, identify defective photon sources, and prevent the defective photon sources from transmitting photons to the photon processing system. The photon source can generate any type of unentangled or entangled photons. The photon processing system can be a resource state generator, a photon detection system, or any other quantum computing device. Various embodiments of the present invention, including methods, processes, systems, devices, etc., are described herein. While the embodiments disclosed herein primarily relate to photon-based systems, the embodiments can be used in any system that uses entangled states.

[0018]

[0024] In one embodiment, multiple spatially multiplexed nondeterministic photon sources are configured to generate photon pairs in response to a trigger signal. At each photon source, photons may be nondeterministically generated in pairs (each pair including a signal photon and a herald photon). During operation of the photon source, "excess" photons may be generated and transmitted to a photon analyzer that determines one or more characteristics of the photons and associated photon sources.

[0019]

[0025] In another embodiment, a photon analyzer can analyze photons exiting a resource state generator, where the photons can be unentangled photons as well as entangled states of two or more photons (e.g., GHZ states, Bell pairs, etc.) The analyzer can determine whether the resource state generator is functioning properly by analyzing the exiting photons and entangled states of the photons.

[0020]

[0026] To better understand features and aspects of characterization of photons and photon sources according to the present disclosure, further context for the present disclosure is provided in the following sections by describing several specific quantum computing architectures that use photon analyzers according to embodiments of the present disclosure. These embodiments, for example, are merely examples, and other embodiments may be used with other quantum computing architectures.

[0021]

[0027] FIG. 1 is a simplified block diagram of a qubit entanglement subsystem 100 of a linear optical quantum computer (LOQC) that can use the photon sources disclosed herein, according to certain embodiments. According to some embodiments, qubit entanglement subsystem 100 can be used to generate qubits (e.g., photons) that include multiple unentangled photons and entangled states of two or more photons (e.g., GHZ states, Bell pairs, etc.). As shown in FIG. 1, qubit entanglement subsystem 100 may include a photon source module 105 optically connected to a resource state generator 110. In one embodiment, photon source module 105 can provide output photons to resource state generator 110 by interconnecting waveguides 115. Resource state generator 110 can receive the output photons, convert them into one or more entangled photon states, and then output these entangled photon states to output waveguide 120 for use by downstream circuitry that can use the entangled states for further analysis. Both photon source module 105 and resource state generator 110 can be coupled to classical computer system 125 such that classical computer system 125 can communicate with and / or control (e.g., via classical information channels 130a, 130b) photon source module 105 and / or resource state generator 110. Classical information channel 130c can communicate between photon source module 105 and resource state generator 110, and classical communication channel 130d can communicate between resource state generator 110 and downstream components.

[0022]

[0028] The qubit entanglement subsystem 100 may include a first photon analyzer 140 coupled to the photon source module 105 and / or a second photon analyzer 145 coupled to the resource state generator 110. In some embodiments, the photon source module 105 and / or the resource state generator 110 may be non-deterministic and thus may generate excess photons and / or photon entangled states for a given generation cycle. The first and second photon analyzers 140, 145, respectively, are configured to characterize these excess photons and / or photon entangled states and use the results to improve and / or diagnose the qubit entanglement subsystem 100. More specifically, in some embodiments, the results from the first and second photon analyzers 140, 145, respectively, can be used to select the highest quality resources within the qubit entanglement subsystem 100 and prioritize those resources for future operations, perform diagnostics of the resources within the qubit entanglement subsystem, perform quantum tomography on the photons and / or photon entangled states generated by the photon source and / or resource state generator, verify the correctness of the entangled states generated by the photon source module and / or resource state generator, or perform other functions. Those skilled in the art will recognize many variations, modifications, and alternative uses of the first and second photon analyzers 140, 145, respectively, and will understand that the photon analyzers can include any number of suitable photon components, such as one or more photon detectors, optical filters, polarizers, birefringent elements, etc.

[0023] photon source

[0029] In some embodiments, the photon source module 105 can be non-deterministic (sometimes referred to as "stochastic"), such that a given pump pulse may or may not produce a photon pair. In some embodiments, coherent spatial and / or temporal multiplexing of several non-deterministic sources (referred to herein as "active" multiplexing) can be used to increase the probability that one mode will be occupied during a given cycle to approach unity. Those skilled in the art will appreciate that many different active multiplexing architectures incorporating spatial and / or temporal multiplexing are possible, some of which are described herein. For example, active multiplexing schemes can be used that use logarithmic trees, generalized Mach-Zehnder interferometers, multimode interferometers, chained sources, dump-to-pump chained sources, asymmetric polycrystalline single-photon sources, or any other type of active multiplexing architecture. In some embodiments, the photon source module 105 can employ active multiplexing schemes, such as those using quantum feedback control. In some embodiments described below, the use of multi-rail coding allows the probability of a band being occupied by one mode during a given pulse cycle to approach unity without active multiplexing.

[0024]

[0030] In one example of such a light source, the light source is driven by a pump (e.g., optical pulse) coupled to an optical resonator that can generate zero, one, or multiple photons by some nonlinear process (e.g., spontaneous four-wave mixing, second-harmonic generation, etc.). As used herein, the term "trial" (also referred to herein as "cycle") is used to refer to the act of driving a photon source with some kind of drive signal (e.g., pump pulse) that can generate output photons non-deterministically (i.e., the probability that the photon source will generate one or more photons in response to the drive signal may be less than 1). In some embodiments, the apparent efficiency of a photon source can be increased by using multiple single-photon sources and multiplexing the output of multiple photon sources, as described in more detail below.

[0025]

[0031] The exact type of photon source used is not important; any type of source can be used, as can any photon generation process, such as spontaneous four-wave mixing (SPFW), spontaneous parametric down-conversion (SPDC), or any other process. Other classes of sources that do not necessarily require nonlinear materials can also be used, such as quantum dot sources, those that use atoms and / or artificial atomic systems, such as color centers in crystals. In some cases, the source may be coupled to a photonic cavity, as in the case of an artificial atomic system, such as a quantum dot coupled to a cavity. Other types of photon sources, such as optomechanical systems, also exist for SPFW and SPDC. In some examples, the photon source can emit multiple photons that are already in an entangled state, in which case the resource state generator 110 may not be required, or an entangled state may be taken as an input to generate an even larger entangled state. More specifically, the photon sources disclosed herein can generate any combination of single and multiple photons in unentangled and / or entangled states. The entangled photon states can include, but are not limited to, Bell states, GHZ states, or more generally, n-qubit Greenberger-Horne-Zeilinger (GHZ) states (also known as "n-GHZ states"), which are entangled quantum states of n qubits (multiple entangled states), or any other entangled states.

[0026]

[0032] In some embodiments, spatial multiplexing of several nondeterministic photon sources (also called MUX photon sources) is used. Many different spatial multiplexing architectures are possible without departing from the scope of this disclosure. Temporal multiplexing can also be implemented instead of or in combination with spatial multiplexing. Multiplexing schemes using logarithmic trees, generalized Mach-Zehnder interferometers, multimode interferometers, chained sources, dump-to-pump chained sources, asymmetric polycrystalline single-photon sources, or any other type of multiplexing architecture can be used. In some embodiments, the photon source can use a multiplexing scheme involving quantum feedback control, etc.

[0027] Resource State Generator

[0033] The resource state generator 110 can receive photons and / or photon entangled states from the photon source module 105, convert them into one or more entangled photon states, and then output these entangled photon states to the output waveguide 120. The entangled photon states can include, but are not limited to, Bell states, GHZ states, or more generally, n-qubit Greenberger-Horn-Zeilinger (GHZ) states (also known as "n-GHZ states"), which are entangled quantum states of n qubits (multiple entangled states), or any other photon entangled states.

[0028]

[0034] In some embodiments, output waveguide 120 can be coupled to downstream circuitry that can use the entangled states to perform quantum computations. For example, the entangled states generated by resource state generator 110 can be used as resources in downstream quantum-optical circuits (not shown).

[0029]

[0035] In some embodiments, because entanglement is also a non-deterministic process, the resource state generator may include one or more analyzers or muxes to generate the appropriate entangled state when needed by downstream systems. In one embodiment, a photon analyzer 145 can be used to verify that the appropriate entangled state has been generated, as described in more detail below. In some embodiments, the resource state generator 110 includes one or more controllers (which may comprise, for example, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICS), etc.) that determine whether each stage of the resource state generator 110 was successful, implement the switching logic described above, and output reference signals to classical channels 130b and / or 130d to inform other components as to whether the resource state generator 110 was successful.

[0030] Classic Computers and Clocks

[0036] In some embodiments, classical computer system 125 includes memory, one or more processors, a power supply, an input / output (I / O) subsystem, and a communication bus for interconnecting these components. The processor(s) may execute modules, programs, and / or instructions stored in the memory, thereby performing processing operations. As described above, qubit entanglement subsystem 100 may include classical channels 130 (e.g., classical channels 130a-130d) for interconnecting and providing classical information between components. In various embodiments, classical computing system 125 may communicate with and / or control (e.g., via classical information channels 130a-130b) photon source module 105 and / or resource state generator 110. Note that classical channels 130a-130d need not all be the same. For example, classical channels 130a-130d may comprise a bidirectional communication bus carrying one or more reference signals (e.g., one or more clock signals), one or more control signals, or any other signals that carry classical information (e.g., herald signals, photon detector readout signals, etc.).

[0031]

[0037] In some embodiments, a system clock signal can be provided to photon source module 105 and resource state generator 110 via an external source (not shown) or by classical computer system 125 generated via classical channels 130a and / or 130b. In some embodiments, the system clock signal provided to photon source module 105 triggers photon source module 105 to attempt to output one photon per interconnecting waveguide 115. In some embodiments, the system clock signal provided to resource state generator 110 triggers or gates a set of detectors in resource state generator 110 to attempt to detect a photon. For example, in some embodiments, triggering a set of detectors in resource state generator 110 to attempt to detect a photon includes gating the set of detectors.

[0032]

[0038] It should be noted that in some embodiments, photon source module 105 and resource state generator 110 may have internal clocks. For example, photon source module 105 may have an internal clock generated and / or used by a controller, and resource state generator 110 has an internal clock generated and / or used by a separate controller. In some embodiments, the internal clocks of photon source module 105 and / or resource state generator 110 are synchronized (e.g., via a phase-locked loop) to an external clock (e.g., a system clock provided by classical computer system 125). In some embodiments, any of the internal clocks may itself be used as a system clock (e.g., the internal clock of photon source module 105 may be distributed to other components in the system and used as a master / system clock).

[0033]

[0039] 2 illustrates a spatially multiplexed qubit entanglement subsystem 200 according to an embodiment of the present disclosure. As shown in FIG. 2, qubit entanglement subsystem 200 may be similar to qubit entanglement subsystem 100, except that qubit entanglement subsystem 200 includes a photon source module 205 configured to generate photon pairs; for simplicity, only one interconnect waveguide 115 is shown coupling photon source module 205 to resource state generator 110, and only one output waveguide 120 is shown coupling the resource state generator to downstream circuitry. Further, more detail is shown within photon source module 205, including multiple spatially multiplexed photon sources 215a...215n, each coupled to a multiplexer 235 and configured to allow the probability of transmitting a photon from interconnect waveguide 115 during a given "trigger" signal 255 to approach unity.

[0034]

[0040] More specifically, in this embodiment, multiple nondeterministic photon sources 215a...215n are configured to each simultaneously attempt to generate photon pairs in response to a trigger signal 255. In some embodiments, trigger signal 255 can be generated by classical computer system 125, and in other embodiments, a different system can generate trigger signal 255. Each photon source 215a...215n can nondeterministically generate photon pairs (each including a signal photon and a herald photon), where one photon (e.g., a herald photon) signals the presence of the other photon (e.g., a signal photon) in the pair. In some embodiments, the photon pairs are unentangled, while in other embodiments, the photon pairs are entangled, and in one embodiment, the photon pairs are Bell state pairs. In another embodiment, each photon source 215a...215n can be configured to generate an entangled state of two or more photons.

[0035]

[0041] Each generated photon pair is sent to a respective splitter 220a...220n, which splits the signal photon from the herald photon. The signal photon is sent to a respective photon detection switch 225a...225n, and the herald photon is sent to a respective photon detector 230a...230n. When a herald photon is detected by a respective detector 230a, the detector generates a detection signal that can be communicated to classical computer system 125, configuring each photon detection switch 225a...225n to route the signal photon from pass-through port 237a...237n to multiplexer 235. If photon detector 230a...230n does not detect a herald photon, each photon detection switch 225a...225n can couple the output of each splitter 220a...220n to a respective emit port 240a...240n. This same process is performed for each of the multiple photon sources 215a...215n each time a trigger signal 255 is sent.

[0036]

[0042] In some embodiments, photon detectors 230a...230n can be implemented by coupling a waveguide to a single-photon detector that generates a classical signal (e.g., a digital logic signal) indicating that a photon has been detected by the detector. Any type of photodetector that is sensitive to single photons can be used. In some embodiments, detection of a photon (e.g., at the output end of the waveguide) can indicate an occupied mode, and the absence of a detected photon can indicate an unoccupied mode.

[0037]

[0043] In some embodiments, only a single signal photon is generated by the multiple photon sources 215a...215n for a given trigger signal 255, and the multiplexer 235 directs the signal photon to the resource state generator 110 via multiple photon routing switches 247a...247n within the multiplexer 235. In other embodiments, two or more photon pairs are generated by the multiple photon sources 215a...215n for a given trigger signal 255, and two or more signal photons are sent to the multiplexer 235. In such cases, because only one photon is needed by the resource state generator 110, there are "excess" photons, at least one of which can be sent to the photon analyzer 260. Any additional photons can be directed to emission ports 240a...240n. In some embodiments, sensing the generated photons during a given trigger signal and directing certain photons to the resource state generator 110, directing certain excess photons to the analyzer 260, and directing any additional photons to the emission ports 240a...240n can be performed by a classical computer system 125.

[0038]

[0044] In response to receiving the signal photon, the photon analyzer 260 determines one or more characteristics of the received signal photon. In some embodiments, the one or more characteristics may include, but are not limited to, color, jitter, wavelength, spectral width, dispersion or delay relative to the trigger cycle that generated the received photon. Accordingly, one skilled in the art will recognize that the photon analyzer may include any number of suitable photon components, such as one or more photon detectors, optical filters, polarizers, birefringent elements, etc. In embodiments in which the photon source module 105 generates an entangled state, the photon analyzer 260 may analyze the entangled state to determine that the correct entangled state has been generated. In further embodiments, quantum tomography may be performed, which may generally be described as the ability to characterize the “unknown” state and dynamics of a quantum system through physical measurements. Quantum tomography is generally performed by generating and analyzing many identical copies of the same state. Different measurements may be performed on each identical copy, and the results may be used to estimate the state and dynamics of the quantum system. In one embodiment, quantum tomography can be used to determine the superposition coefficients of the wave functions of the entangled states. Those skilled in the art, having the benefit of this disclosure, will recognize many other photon and entangled photon properties that can be determined.

[0039]

[0045] In some embodiments, the photon analyzer 260 can determine which photon source 215a...215n generated a signal photon by receiving a detection signal from the detectors 230a...230n. In other embodiments, the photon analyzer 260 can use other data to determine which photon source 215a...215n generated a signal photon, including identifying specific characteristics of the signal photon associated with a particular photon source. In one example, a slight shift in the wavelength of each signal photon can be used to distinguish which photon source 215a...215n generated a particular photon. In some embodiments, each photon source module 105 and each resource state generator 110 may include two or more photon analyzers 260 for analyzing photons generated from multiple generators.

[0040]

[0046] During normal operation of the photon source module 205, many photons are generated by each photon source 215a...215n. This allows the photon analyzer 260 to collect data regarding the photons generated by each of the photon sources 215a...215n that indicates the performance of each photon source. In one embodiment, the photon analyzer 260 ranks each photon source 215a...215n according to one or more characteristics of the photons each source generates and uses that data to rank the photon sources from best to worst quality. Using this data in future cases where two or more photon pairs are generated by multiple photon sources 215a...215n, the classical computer system 125 can use the data generated by the photon analyzer 260 to route the highest quality signal photon to the resource state generator 110 and send one of the remaining signal photons to the photon analyzer 260, thereby continuously updating metrics regarding the performance of each photon source 215a...215n.

[0041]

[0047] In a further embodiment, the photon analyzer 260 can compare one or more characteristics of each signal photon to a threshold to detect "faulty" photon sources 215a...215n. In response, the classical computer system 125 can send one or more signals that prevent signal photons generated by the faulty photon source from being routed to the resource state generator 110. In a further embodiment, if a faulty photon source is identified, the photon source module 105 can switch in a redundant photon source in place of the faulty photon source.

[0042]

[0048] In some embodiments, it may be beneficial to redirect signal photons after they have been routed by the multiplexer 235. This feature allows for analysis of the effect of the photon routing bus 275 extending between the multiplexer 235 and the resource state generator 110, or allows photons generated by the high-quality photon sources 215a...215n to be directed to the photon analyzer 260 for characterization. In some embodiments, photon rerouting can be achieved with a crossover switch 265 disposed between the multiplexer 235 and the resource state generator 110 / photon analyzer 260. In various embodiments, the crossover switch 265 can be configured to redirect signal photons directed by the multiplexer 235 to the resource state generator 110 to the photon analyzer 260, and to redirect signal photons directed by the multiplexer 235 to the photon analyzer 260 to the resource state generator 110. These and other features are described in more detail below. Although the embodiments disclosed herein relate primarily to photon-based systems, the embodiments can be used in any system that uses entangled states.

[0043]

[0049] Figure 3 illustrates a spatially multiplexed qubit entanglement subsystem 300 according to an embodiment of the present disclosure. As shown in Figure 3, qubit entanglement subsystem 300 may be similar to qubit entanglement subsystem 200 illustrated in Figure 2, except that qubit entanglement subsystem 300 includes three non-deterministic photon sources 215a...215c, where the paths of photon pairs generated by each respective generator are shown for one trigger signal 255.

[0044]

[0050] The first and third photon sources 215a and 215c each generate a first and third photon pair 307a, 307c, respectively, in response to a particular trigger signal, while the second photon source 215b did not generate a photon pair during this particular trigger signal. In this example, the first photon pair 307a generated by the first photon source 215a is represented by a circle, with a vertical line within the circle indicating a pair of signal photons 308a and a horizontal line indicating a pair of herald photons 309a. Similarly, the third photon pair 307c of the third photon source 215c is represented by a square, with a vertical line within the square indicating a pair of signal photons 308c and a horizontal line indicating a pair of herald photons 309c.

[0045]

[0051] 3, the first photon pair 307a is transmitted to a first splitter 220a, which splits the first photon pair into a first signal photon 308a and a first herald photon 309a. The first herald photon 309a is transmitted to a first detector 230a, and a first detected signal 233a is transmitted to a first photon detection switch 225a. In response, the first photon detection switch 225a routes the first signal photon 308a to a first photon routing switch 247a in the photon multiplexer 235. In some embodiments, the photon detection and routing signals can be processed by one or more internal classical computing resources, an external classical computer system 125, or a combination thereof.

[0046]

[0052] As noted above, second photon source 215b did not generate a photon pair during this particular trigger signal. Third photon pair 307c is transmitted to third splitter 220c, which splits the third photon pair into third signal photon 308c and third herald photon 309c. Third herald photon 309c is transmitted to third detector 230c, and third detected signal 233c is transmitted to third photon detector switch 225c. In response, third photon detector switch 225c routes third signal photon 308c to third photon routing switch 247c.

[0047]

[0053] The classical computer system 125 receives the first and third detection signals 233a, 233c, respectively, and, based on the generation of the first and third photon pairs 307a, 307c, respectively, changes the state of the first photon routing switch 247a and the third photon routing switch 247c in the multiplexer 235 to direct the first signal photon 308a to the resource state generator 110 and direct the third signal photon 308c to the photon analyzer 260. However, in this embodiment, the classical computer system 125 couples the crossover switch 265 such that the first signal photon 308a routed by the first photon routing switch 247a to the resource state generator 110 is routed to the photon analyzer 260. Similarly, the third signal photon 308c routed by the third photon routing switch 247c to the photon analyzer 260 is now routed to the resource state generator 110. In some embodiments, the crossover switch 265 may be useful for determining any effect of the photon processing system bus 275 on photons passing through the bus. In further embodiments that may have a small number of high-quality photon sources, photons generated by these high-quality photon sources may not be routed, or may be routed very little, to the photon analyzer 260. Thus, the crossover switch 265 may route photons from any photon source to the photon analyzer 260 to maintain continuous characterization of all photon pairs. Those skilled in the art, having the benefit of this disclosure, will recognize many other uses for the crossover switch 265.

[0048]

[0054] 4 illustrates steps associated with a method 400 for generating signal photons for a resource state generator and analyzing excess photons to determine characteristics of one or more photon sources, according to some embodiments of the present disclosure. As shown in FIG. 4, method 400 begins at step 405, in which a trigger signal is generated by a qubit entanglement subsystem. The qubit entanglement subsystem can use one or more photon sources that non-deterministically generate photon pairs in response to the photon source receiving the trigger signal. As mentioned above, such embodiments are not limited to photon sources that generate photon pairs; the photon source can generate any combination of unentangled or entangled states of two or more photons.

[0049]

[0055] In step 410, in response to the trigger signal, a first photon source generates a first photon pair. The first photon pair can include a first signal photon and a first herald photon. In other embodiments, multiple pairs of photons or entangled states of photons can be generated.

[0050]

[0056] In step 415, in response to the trigger signal, a second photon source generates a second photon pair. The second photon pair can include a second signal photon and a second herald photon. In some other embodiments, multiple pairs of photons or entangled states of photons can be generated.

[0051]

[0057] In step 420, the first signal photon is separated from the first herald photon in the first pair of photons. In one embodiment, the separation can be performed using a wavelength division splitter or other suitable device. The first signal photon can be transmitted from a first splitter port, and the first herald photon can be transmitted from a second splitter port.

[0052]

[0058] In step 425, the second signal photon is separated from the second herald photon in the second pair of photons. In one embodiment, the separation can be performed using a wavelength division splitter or other suitable device. The second signal photon can be transmitted from a primary splitter port, and the first herald photon can be transmitted from a secondary splitter port.

[0053]

[0059] The first herald photon may be detected using a first detector coupled to the second splitter port in step 430. In response to detecting the first herald photon, the first detector may transmit a first detection signal.

[0054]

[0060] The second herald photon may be detected using a second detector coupled to the secondary splitter port in step 435. In response to detecting the second herald photon, the second detector may transmit a second detection signal.

[0055]

[0061] The state of the first photon detecting switch is changed to pass the first signal photons in step 440. In some embodiments, the state of the first photon detecting switch is changed in response to a first detection signal transmitted by the first detector.

[0056]

[0062] The state of the second photon detecting switch is changed to pass the second signal photons in step 445. In some embodiments, the state of the second photon detecting switch is changed in response to a second detection signal transmitted by the second detector.

[0057]

[0063] In step 450, the first photon routing switch is configured to route the first signal photon from the first photon detection switch to the resource state generator. In some embodiments, the first photon routing switch can be configured by detection logic or a classical computer system, as described in more detail herein.

[0058]

[0064] In step 455, the second photon routing switch is configured to route the second signal photons from the second photon detection switch to the photon analyzer. In some embodiments, the second photon routing switch can be configured by detection logic or a classical computer system, as described in more detail below.

[0059]

[0065] In some embodiments, the detection logic is configured to receive the first and second detection signals and configure the first and second photon routing switches to send a single source photon to the resource state generator in response to each trigger signal. In embodiments where only one detection signal is received, the detection logic configures the corresponding photon routing switch to send a signal photon to the resource state generator. In embodiments where more than one detection signal is received, the detection logic configures one photon routing switch to send a corresponding signal photon to the resource state generator and a separate signal photon to the photon analyzer. In further embodiments, as described in more detail herein, the detection logic can operate in conjunction with data obtained by the photon analyzer to select the highest quality photons to send to the resource state generator.

[0060]

[0066] In step 460, the second signal photons are received at a photon analyzer.

[0061]

[0067] In step 465, in response to receiving the second signal photon, the photon analyzer determines one or more characteristics of the second signal photon. In some embodiments, the one or more characteristics may include, but are not limited to, color, jitter, wavelength, spectral width, dispersion or delay relative to the clock cycle that generated the received photon. Those skilled in the art with the benefit of this disclosure will recognize many other characteristics that may be determined. In some embodiments, the photon analyzer can determine which photon source generated the signal photon by receiving a detection signal from the detector. In other embodiments, the photon analyzer can use other data to determine which photon source generated the signal photon, including identifying specific characteristics of the signal photon associated with a particular photon source. In one example, a slight shift in the wavelength of each signal photon can be used to discern which photon source generated a particular photon, and that data can be used to determine the characteristics of each photon source. In embodiments in which a photon source generates an entangled state of two or more photons, the photon analyzer can perform quantum tomography on the entangled state.

[0062]

[0068] It will be understood that method 400 is illustrative and that variations and modifications are possible. Steps described as sequential may be performed in parallel, the order of steps may be changed, and steps may be modified, combined, added, or omitted. Although method 400 has been described and illustrated using two photon sources, any number of photon sources and any physical layout may be used.

[0063]

[0069] 5 illustrates steps associated with a method 500 for generating and controlling the quality of signal photons for a resource state generator, according to some embodiments of the present disclosure. As shown in FIG. 5, in method 500, step 505 begins with receiving a trigger signal by one or more photon sources. In some embodiments, a photon processing system can benefit from a photon source that deterministically generates a single signal photon in response to providing the photon source with a trigger signal.

[0064]

[0070] In step 510, in response to a trigger signal, multiple photon sources generate multiple photon pairs. Each photon pair can include a signal photon and a herald photon. In other embodiments, multiple pairs can be generated, and in further embodiments, photon entanglement states can be generated.

[0065]

[0071] For each photon pair generated, the signal photon is separated from the herald photon in step 515. In one embodiment, the separation can be performed using a wavelength division splitter or other suitable device.

[0066]

[0072] In step 520, the herald photon of each generated photon pair may be detected by a respective detector. In response to detecting the herald photon, each detector may transmit a respective detection signal. In some embodiments, detection logic may receive one or more detection signals, while in other embodiments, a classical computer system may receive one or more detection signals.

[0067]

[0073] In step 525, it is determined whether two or more herald photons are detected. In some embodiments, the detection logic can make the determination. If only one herald photon is detected, there is only one signal photon, and the detection logic proceeds to step 530, causing the signal photon to be sent to the resource state generator. If there are two or more detected herald photons, there are two or more generated signal photons, and processing proceeds to step 535. In step 535, the detection logic, in conjunction with the photon analyzer, can determine which signal photon has the highest quality based on previously characterized photons from each photon source. In step 540, the photon routing switch is configured to route the highest quality photon to the resource state generator, and the second signal photon is routed to the photon analyzer. In this manner, only the highest quality signal photon is sent to the resource state generator.

[0068]

[0074] It will be understood that method 500 is illustrative and that variations and modifications are possible: steps described as sequential may be performed in parallel, the order of steps may be changed, and steps may be modified, combined, added, or omitted.

[0069]

[0075] Figure 6 illustrates a time-multiplexed qubit entanglement subsystem 600 according to an embodiment of the present disclosure. As shown in Figure 6, qubit entanglement subsystem 600 may be similar to spatially multiplexed qubit entanglement subsystem 300 (shown in Figure 3), except that time-multiplexed qubit entanglement subsystem 600 includes two time-multiplexed non-deterministic photon sources 215a...215c that can direct generated photons through a variable delay 620 to a resource state generator, as described in more detail below.

[0070]

[0076] In the entanglement subsystem 600 of FIG. 6 , the classical computer system 125 includes a master clock 605 that controls the operation of the photon sources 215 a, 215 b and the resource state generator 110. More specifically, in this exemplary embodiment, the resource state generator 110 requires a photon from the photon source module 610 per clock cycle, represented by the resource state generator trigger 615 with the notation “1X.” In comparison, the classical computer system 125 sends four trigger signals 255, represented by the notation “4X,” to the photon sources 215 a, 215 b per resource state generator trigger 615. That is, the photon sources 215 a, 215 b are triggered four times more frequently than the resource state generators. This four-to-one ratio allows for the use of fewer photon sources without losing photon generation opportunities. That is, every resource state generator clock cycle is supplied by two photon sources, each operating four times, for a total of eight photon generation cycles. By comparison, a spatially multiplexed design requires eight photon sources to have eight photon generation cycles per resource state generator clock cycle. Thus, the nondeterminism of the photon sources can be overcome by spatially and / or temporally multiplexing the photon sources. Those skilled in the art, having the benefit of this disclosure, will recognize many other configurations of temporally multiplexed photon sources, including one photon source that can operate multiple times (e.g., 2X, 4X, 10X, 100X, 1000X) for all resource state generator clock cycles and any other combinations and cycle ratios of photon sources.

[0071]

[0077] As further shown in FIG. 6 , multiplexer 235 is coupled to classical computer system 125, which tracks when photons are generated and directs them to resource state generator 110 and / or photon analyzer 260 accordingly. In a time-multiplexed system, an additional variable delay 620 can be placed between multiplexer 235 and the resource state generator, although other embodiments can use other system architectures to accommodate a four-to-one ratio. In this particular example, upon a first trigger signal 255 sent to the photon source, a photon is generated and is not needed by resource state generator 110 until the fourth clock cycle, so that the photon can be held in a “three-cycle” bin within variable delay 620. This delays the photon from being sent to resource state generator 110 for the next three cycles, until the fourth clock cycle. If a second photon is generated during the first cycle, classical computer system 125 can direct that photon via multiplexer 235 to photon analyzer 260. At this point, there are already photons waiting for the resource state generator 110 so any further photons generated in the following clock cycle can be sent to the photon analyzer 260 .

[0072]

[0078] The operation of the variable delay 620 is similar if no photons are generated in the first cycle but one photon is generated in the second cycle. The classical computer system 125 directs that photon to the “two-cycle” bin and delays it for the next two cycles until the fourth cycle, after which it is released to the resource state generator 110. Any other photons generated can be considered “excess” and sent to the photon analyzer 260. Similar operations are performed if one or more photons are generated only in the third and / or fourth cycles. Those skilled in the art, with the benefit of this disclosure, will recognize many variations, modifications, and alternatives for delaying and forwarding generated photons in a temporally multiplexed photon source architecture. As described herein, the photon sources 215a, 215b can generate any type or combination of unentangled or entangled photons, including one, two, or more photons.

[0073]

[0079] 7 is a simplified block diagram of an example linear optical quantum computer (LOQC) 700 that can employ the spatially and / or temporally multiplexed photon sources disclosed herein, according to certain embodiments. The LOQC 700 can include multiple photon sources 715 in a photon source module 705, a linear optical quantum computing circuit operating as a resource state generator 710, a reconfigurable single-photon detection circuit 720, and a classical computer 730. Each photon source 715 can be configured to deterministically (or nearly deterministically) generate a sequence of photons that can be used as a quantum bit. In some embodiments, the photon sources 715 can include cascaded (or multiplexed) photon sources, for example, based on spontaneous four-wave mixing (SFWM) or spontaneous parametric down-conversion (SPDC) in a passive nonlinear optical medium. At each photon source 715, photons may be generated non-deterministically in pairs (signal photons and herald photons), with one photon (e.g., a herald photon) signaling the presence of the other photon (e.g., a signal) in the pair. Thus, when a herald photon is detected at one photon source, the corresponding signal photon may be used as the output of the photon source, and other photon sources in the cascade (or multiplexed) photon source may be sent to the photon analyzer 740. However, in other embodiments, photon source 715 may be used to generate any quantity and / or type of photons, unentangled photons or entangled photon-entangled states, as described in more detail herein.

[0074]

[0080] The photon analyzer 740 can determine one or more characteristics of each received “excess” photon and / or photon entangled state generated from the photon source module 705. In some embodiments, the one or more characteristics can include, but are not limited to, color, jitter, wavelength, spectral width, dispersion or delay relative to the clock cycle that generated the received photon. In other embodiments in which a photon source generates an entangled state of two or more photons, the photon analyzer 740 can perform quantum tomography on the excess entangled state. Those skilled in the art with the benefit of this disclosure will recognize many other characteristics of the photons and / or photon sources that can be determined by the photon analyzer 740. In some embodiments, the photon analyzer can determine which photon source generated the photon and / or photon entangled state by receiving a detection signal from an associated detector. In other embodiments, the photon analyzer can use other data to determine which photon source generated the photon and / or entangled state, including identifying specific characteristics of the photon and / or entangled state associated with a particular photon source. In one example, a slight shift in the wavelength of each signal photon can be used to distinguish which photon source generated a particular photon.

[0075]

[0081] In some embodiments, the photon analyzer 740 can be used to optimize the performance of each photon source 715 by selecting photons from the highest quality photon source and routing "excess" photons to a photon analyzer or termination port. In further embodiments, the photon analyzer 740 can determine whether a photon source has generated a proper photon entangled state by performing quantum tomography.

[0076]

[0082] The resource state generator 710 may include a network of waveguides, beam splitters, phase shifters, delay lines, and other photonic components and circuits that may be used to implement optically controlled NOT (CNOT) gates to generate Bell states and fusion gates to generate larger entangled states that can be stored in delay lines.

[0077]

[0083] The cluster analyzer 745 can be used to perform analysis of the over-entangled states of photons generated by the resource state generator 710. More specifically, in one embodiment, the cluster analyzer 745 can analyze the entangled states of two or more photons to determine that the correct entangled state has been generated. In a further embodiment, quantum tomography can be performed by generating and analyzing many identical copies of the same state. Different measurements can be performed on each identical copy, and the results can be used to infer the state and dynamics of the quantum system. In one embodiment, quantum tomography can be used to determine the superposition coefficients of the wave functions of the entangled states.

[0078]

[0084] The reconfigurable single-photon measurement circuit 720 may include multiple single-photon detectors configured to measure single photons (qubits) in an entangled state based on some measurement pattern, sometimes referred to as a measurement mask.

[0079]

[0085] Classical computer 730 can decode the photon results measured by single-photon measurement circuit 720 and perform some logical processing to generate computational results. In some embodiments, classical computer 730 can feed back the decoding results to single-photon measurement circuit 720. For example, based on the decoding results, classical computer 730 can adjust some measurement masks or determine some measurement masks that have not been predetermined for use by single-photon measurement circuit 720.

[0080]

[0086] The Linear Optical Quantum Computer (LOQC) 700 can include millions of optical components such as couplers, resonators, single-photon detectors, beam splitters, interferometers, switches, phase shifters, and delay lines. According to certain embodiments, these optical components can be fabricated using semiconductor process technology as photonic integrated circuits (PICs) on semiconductor wafers, such as silicon photonic integrated circuits on silicon wafers. 7

[0081]

[0087] The linear optical quantum computer (LOQC) 700 may also include numerous electronic integrated circuits (EICs) containing, for example, control logic, switches, etc. for the Herald single-photon source. To achieve high performance (e.g., high speed), it may be necessary to minimize the interconnections between the electronic circuits and the photonic integrated circuits. Furthermore, many components of the LOQC 700 may need to operate at cryogenic temperatures, such as below 140 K or below 5 K, to achieve desired performance.

[0082]

[0088] In some embodiments, a qubit, typically described herein as a photon, can be a quantum system and / or collection of particles and can be formed using any qubit architecture. For example, a quantum system can be a particle such as an atom, ion, nucleus, and / or photon. In other examples, a quantum system can be a flux qubit, a phase qubit, or other engineered quantum systems, such as a charge qubit (e.g., formed from superconducting Josephson junctions), a topological qubit (e.g., Majorana fermions), or a spin qubit formed from vacancy centers (e.g., nitrogen vacancies in diamond). Furthermore, while the term "qubit" is used herein for clarity, systems can also use quantum information carriers that encode information in a manner not necessarily associated with binary bits. For example, according to some embodiments, a qubit (i.e., a quantum system capable of encoding information in three or more quantum states) can be used.

[0083]

[0089] Those skilled in the art will appreciate that substantial variations may be made in accordance with particular implementations. For example, customized hardware may be used and / or particular elements may be implemented in hardware, software (including portable software such as applets), or both. Furthermore, connection to other computing devices, such as network input / output devices, may be employed.

[0084]

[0090] With reference to the accompanying drawings, components that may include memory may also include non-transitory machine-readable media. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any storage medium that participates in providing data that causes a machine to operate in a specific manner. In the embodiments provided above, various machine-readable media may participate in providing instructions / code to a processor and / or other devices for execution. Additionally or alternatively, machine-readable media may be used to store and / or transport such instructions / code. In many implementations, computer-readable media are physical and / or tangible storage media. Such media can 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 tape, any other physical medium with a pattern of holes, RAM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described below, or any other medium from which a computer can read instructions and / or code.

[0085]

[0091] The methods, systems, and devices described herein are examples. Various embodiments may omit, substitute, or add various procedures or components as appropriate. For example, features described with respect to particular embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. Various components of the diagrams provided herein may be implemented in hardware and / or software. Also, technology evolves, and therefore many of the elements are examples that do not limit the scope of the disclosure to those specific examples.

[0086]

[0092] It has proven convenient at times, primarily for reasons of common usage, to refer to signals as bits, information, values, elements, symbols, characters, variables, terms, numbers, numerals, or the like. It should be understood, however, that all of these or similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless otherwise indicated, and as is clear from the above description, throughout this specification, descriptions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” “ascertaining,” “identifying,” “associating,” “measuring,” “performing,” and the like, are understood to refer to operations or processes of a specific apparatus, such as a special purpose computer or similar special purpose electronic computing device. Thus, in the context of this specification, a special purpose computer or similar special purpose electronic computing device can manipulate or transform signals, which are typically represented as physical electronic, electrical, or magnetic quantities in memories, registers, or other information storage, transmission, or display devices of the special purpose computer or similar special purpose electronic computing device.

[0087]

[0093] Those skilled in the art will appreciate that the information and signals used to communicate the messages described herein may be represented using any of a variety of different technologies and techniques. For example, the data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0088]

[0094] As used herein, the terms “and,” “or,” and “and / or” can have a variety of meanings, which are expected to depend at least in part on the context in which such terms are used. Typically, “or” when used to associate a list, such as A, B, or C, is intended to mean A, B, and C, which is used herein in an inclusive sense, and similarly, it is intended to mean A, B, or C, which is used herein in an exclusive sense. Furthermore, as used herein, the term “one or more” may be used to describe any feature, structure, or characteristic in the singular, or it may be used to describe several combinations of features, structures, or characteristics. However, it should be noted that this is merely an example, and claimed subject matter is not limited to this example. Furthermore, the term “at least one of,” when used to associate a list, such as A, B, or C, can 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.

[0089]

[0095] Throughout this specification, references to "one example," "an example," "certain examples," or "exemplary implementation" mean that a particular feature, structure, or characteristic described in connection with a feature and / or example may be included in at least one feature and / or example of the claimed subject matter. Thus, appearances of the phrases "in one example," "an example," "in certain examples," "in certain implementations," or other similar phrases in various places throughout this specification do not necessarily 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 characteristics.

[0090]

[0096] In some implementations, operations or processing may involve physical manipulations of physical quantities. Typically, though not necessarily, such quantities may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals, or the like. It should be understood, however, that all of these or similar terms are to be associated with the appropriate physical quantities and are merely convenient labels. Unless otherwise indicated, and as will be apparent from the description herein, descriptions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” and the like throughout this specification will be understood to refer to operations or processing of a specific apparatus, such as a special purpose computer, a special purpose computing apparatus, or a similar special purpose electronic computing device. Thus, in the context of this specification, a special purpose computer or similar special purpose electronic computing device can manipulate or transform signals that are normally represented as physical electronic or magnetic quantities within the memory, registers, or other information storage, transmission, or display devices of the special purpose computer or similar special purpose electronic computing device.

[0091]

[0097] In the foregoing detailed description, numerous specific details are set forth to provide a thorough understanding of the claimed subject matter. However, it will be understood by those skilled in the art that the claimed subject matter may be practiced without these specific details. In other instances, methods and apparatuses known to those skilled in the art have not been described in detail so as not to obscure the claimed subject matter. Therefore, it is intended that the claimed subject matter not be limited to the particular examples disclosed, and that such claimed subject matter also include all aspects falling within the scope of the appended claims and equivalents thereof.

[0092]

[0098] For embodiments involving firmware and / or software, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Any machine-readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software code may be stored in a memory and executed by a processor unit. The memory may be implemented within the processor unit or external to 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 or number of memories or the type of medium on which the memory is stored.

[0093]

[0099] If implemented in firmware and / or software, the functions may be stored as one or more instructions or code on a computer-readable storage medium. Examples include computer-readable media encoded with data structures and computer-readable media encoded with a computer program. Computer-readable media include physical computer storage media. Storage media may be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may comprise RAM, ROM, EEPROM, compact disk read-only memory (CD-ROM) or other optical disk storage devices, magnetic disk storage devices, semiconductor storage devices, or other storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. As used herein, disk and disk include compact disks (CDs), laser disks, optical disks, digital versatile disks (DVDs), floppy disks, and Blu-ray disks; disks typically reproduce data magnetically, while disks reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0094]

[0100] In addition to being stored on a computer-readable storage medium, the instructions and / or data may be provided as signals on a transmission medium included in a communications device. For example, the communications device may include a transceiver having signals indicative of the instructions and data. The instructions and data are configured to cause one or more processors to perform the functions outlined in the claims. That is, the communications device includes a transmission medium having signals indicative of information for performing the disclosed functions. At a first time, the transmission medium included in the communications device may include a first portion of information for performing the disclosed functions, and at a second time, the transmission medium included in the communications device may include a second portion of information for performing the disclosed functions.

Claims

1. A plurality of photon pair sources, each of the plurality of photon pair sources comprising: a photon source configured to generate photon pairs including a signal photon and a herald photon in response to a trigger signal; a splitter having a splitter input port, a first splitter output port, and a second splitter output port, the splitter input port configured to couple to the photon source and to output the signal photons at the first splitter output port and the herald photons at the second splitter output port; a detector having a detector input port coupled to the second splitter output port, the detector configured to detect the herald photons; a photon detecting switch having a switch input port, a first switch output port, and a second switch output port, the switch input port coupled to the first splitter output port; a plurality of photon pair sources comprising: a photon multiplexer having a plurality of photon routing switches, each of the plurality of photon routing switches corresponding to one of the plurality of photon pair sources, each of the plurality of photon routing switches comprising: an input port coupled to the first switch output port of a corresponding one of the photon detecting switches; a first multiplexer output port coupled to a photon analyzer; a second output port for coupling to a photon processing system; a photon multiplexer comprising: A quantum computing system comprising:

2. The quantum computing system of claim 1 , wherein the photon multiplexer directs the signal photons to the photon processing system when the multiple photon pair sources emit one photon per trigger signal.

3. 2. The quantum computing system of claim 1, wherein the photon multiplexer directs one of the signal photons to the photon analyzer when the multiple photon pair sources emit two or more photons per trigger signal.

4. The quantum computing system of claim 1 , wherein the photon processing system is a resource state generator.

5. The quantum computing system of claim 1 , wherein the photon pairs include photons in an entangled state.

6. The quantum computing system of claim 1, wherein the photon source is a plurality of spatially multiplexed photon sources.

7. The quantum computing system of claim 1, wherein the photon source is a plurality of temporally multiplexed photon sources.

8. a first photon source configured to generate first photon pairs, each first photon pair including a first signal photon and a first herald photon; a second photon source configured to generate second photon pairs, each second photon pair including a second signal photon and a second herald photon; a first detector configured to generate a first detection signal in response to detecting the first herald photon; a second detector configured to generate a second detection signal in response to detecting the second herald photon; detection logic configured to direct one of the first signal photons or the second signal photons to a photon analyzer and direct one of the first signal photons or the second signal photons to a photon processing system in response to detection logic receiving the first detection signal and the second detection signal; A device with.

9. 9. The device of claim 8, further comprising a multiplexer that, in response to receiving one or more signals from the detection logic, routes the one of the first signal photons or the second signal photons to the photon analyzer and routes the one of the first signal photons or the second signal photons to the photon processing system.

10. 9. The device of claim 8, wherein the detection logic directs the first and second signal photons based on a quality level of each of the first and second signal photons.

11. The device of claim 8 , wherein in response to receiving the first signal photon or the second signal photon, the photon analyzer determines one or more characteristics of the received signal photon.

12. The device of claim 11 , wherein the one or more characteristics include color, jitter, wavelength, spectral width, or dispersion.

13. 9. The device of claim 8, wherein during repeated operation of the first photon source and the second photon source, the photon analyzer determines one or more characteristics of first signal photons generated by the first photon source and one or more characteristics of second signal photons generated by the second photon source.

14. The device of claim 13 , wherein the photon analyzer compares one or more characteristics of the first signal photons to one or more characteristics of the second signal photons.

15. The device of claim 14 , wherein the photon analyzer, in response to the comparison, sends instructions to the photon processing system to receive more first signal photons than second signal photons.

16. 10. The device of claim 9, further comprising a crossover switch that redirects signal photons routed by the multiplexer to the photon analyzer to the photon processing system.

17. generating a first photon pair using a first photon source, the first photon pair including a first signal photon and a first herald photon; generating a second photon pair using a second photon source, the second photon pair including a second signal photon and a second herald photon; generating a first detection signal in response to detecting the first herald photon; generating a second detection signal in response to detecting the second herald photon; in response to detection logic receiving the first detection signal and the second detection signal, routing one of the first signal photons or the second signal photons to a photon analyzer and routing one of the first signal photons or the second signal photons to a photon processing system; 1. A method for generating photons, comprising:

18. 18. The method of claim 17, wherein the routing is performed by a multiplexer controlled by the detection logic.

19. 20. The method of claim 18, wherein the detection logic directs the multiplexer to route first and second signal photons based on a quality level of each of the first and second signal photons.

20. 20. The method of claim 17, wherein in response to receiving the first signal photon or the second signal photon, the photon analyzer determines one or more characteristics of the received signal photon.

21. The method of claim 20 , wherein the one or more characteristics include color, jitter, wavelength, spectral width, or dispersion.

22. 22. The method of claim 21 , wherein during repeated operation of the first photon source and the second photon source, the photon analyzer determines one or more characteristics of the first signal photons and one or more characteristics of the second signal photons.

23. 23. The method of claim 22, wherein in response to the determination of the one or more characteristics of the first signal photons and the second signal photons, the photon analyzer sends instructions to the photon processing system to receive more first signal photons than second signal photons.

24. a plurality of photon sources, each configured to non-deterministically generate photon pairs in response to receiving a trigger signal, each photon pair including a signal photon and a herald photon; a plurality of photon detectors, each coupled to a respective photon source of the plurality of photon sources and configured to generate a respective detection signal upon detecting the herald photon of each generated photon pair; a plurality of photon routing switches, each coupled to a respective photon source and configured to direct respective said signal photons to a photon processing system or photon analyzer; a photon detection logic circuit configured to receive each respective detection signal and, in response to receiving two or more detection signals per trigger signal, send control signals to the plurality of photon routing switches to route one signal photon to the photon analyzer and one signal photon to the photon processing system; 1. A photon source module comprising:

25. 25. The photon source module of claim 24, wherein in response to receiving the signal photon, the photon analyzer determines one or more characteristics of the signal photon.

26. 26. The photon source module of claim 25, wherein after receiving a plurality of trigger signals, said photon analyzer determines one or more characteristics of signal photons generated by each of said plurality of photon sources and ranks the quality of each of said plurality of photon sources.

27. 27. The photon source module of claim 26, wherein in response to receiving two or more detection signals per trigger signal, the photon analyzer sends one or more signals that cause signal photons from the highest quality photon source to be routed to the photon processing system.

28. The photon source includes a plurality of multiplexed photon sources; The quantum computing system of claim 1 , wherein each of the plurality of multiplexed photon sources is configured to simultaneously emit one or more photons per trigger signal.

29. The quantum computing system of claim 1 , further comprising a crossover switch coupled to the photon multiplexer, the photon processing system, and the photon analyzer.

30. The photon multiplexer comprises: coupled to the photon processing system and the photon analyzer; 10. The quantum computing system of claim 1, configured to simultaneously output a first plurality of emitted photons to the photon processing system and a second plurality of emitted photons to the photon analyzer.

31. The quantum computing system of claim 1 , further comprising at least one internal clock synchronized to an external clock.

Images