Maintaining an established pairwise entanglement buffer for efficient quantum entanglement dispersion.

Abstract

A technique is disclosed for generating and maintaining buffers of on-demand pairwise entangled quantum instances using a programmable optical switchboard architecture within a quantum repeater. The speed at which pairwise entangled quantum instances are established between quantum repeaters of a quantum entanglement network may be higher than both the decay rate of the instances and the consumption rate of the instances to provide distributed quantum entanglement, so as to be able to provide customers with on-demand distribution of quantum entanglement. Furthermore, an optical switchboard having a given quantum repeater may be configured to route between any of the quantum memory locations provided within the quantum repeater, thereby ensuring optimization of the use of such buffers of entangled quantum instances.

Description

BACKGROUND ART

[0001] Quantum computing utilizes the laws of quantum physics to process information. Quantum physics is a theory that describes the behavior of reality at the fundamental level. It is currently the only physical theory that can consistently predict the behavior of microscopic quantum objects (e.g., particles) such as photons, molecules, atoms, and electrons.

[0002] A quantum computing device is a device that leverages quantum mechanics to enable writing, storing, processing, and reading out of information encoded in quantum states, for example, the states of quantum objects. A quantum object is a physical object that behaves in accordance with the laws of quantum physics. The state of a physical object is a description of the object at a given time.

[0003] In quantum mechanics, the state of a two-level quantum system, or simply a qubit, is a list of two complex numbers, where the sum of the squares of the absolute values of the complex numbers (e.g., |x| 2 +|y| 2 ) must add up to 1. Each of the two complex numbers (e.g., x and y) is referred to as an amplitude, and their respective pseudo-probabilities are the squares of the absolute values of the complex numbers (e.g., |x| 2 and |y| 2 ). Accordingly, the square of the absolute value of each complex number corresponds to the probability that event 0 or event 1 will occur. The fundamental and counterintuitive difference between a probabilistic bit (e.g., a conventional 0 or 1 bit) and a qubit is that while a probabilistic bit represents a lack of information about a two-level classical system, a qubit contains the maximum possible information about a two-level quantum system.

[0004] Quantum computing devices are based on qubits, which are quantum bits capable of experiencing the phenomena of "superposition" and "entanglement." Superposition allows a quantum system to be in multiple states simultaneously. For example, while classical computers are based on bits that are either 0 or 1, qubits can be both 0 and 1 at the same time, with different probabilities assigned to 0 and 1. Entanglement is a strong correlation between quantum particles, resulting in them being harmoniously and inseparably linked, even when separated by large distances. [Overview of the project] [Means for solving the problem]

[0005] There are different types of qubits that can be used in quantum computers, each with different advantages and disadvantages. For example, some quantum computers may include qubits constructed from superconductors, trapped ions, semiconductors, photons, etc., each of which may experience different levels of interference, error, and decoherence. Also, some may be more useful for generating certain types of quantum circuits or quantum algorithms, while others may be more useful for generating other types of quantum circuits or quantum algorithms. [Brief explanation of the drawing]

[0006] [Figure 1] This describes, in several embodiments, a service provider network resource that provides quantum entanglement distribution to customer endpoints connected to intermediate quantum repeater nodes in a trust-free region outside of the trusted locations of the service provider network. [Figure 2] We show two quantum repeaters configured, according to several embodiments, to maintain a buffer of established pairwise entanglement instances using each quantum memory location within the repeater. [Figure 3]We demonstrate how quantum entanglement can be extended by performing Bell state measurements between the received particles of each set of entangled particles and the particles in the quantum memory locations of the established pairwise quantum entanglement instances in each quantum repeater location, according to several embodiments. [Figure 4] Examples of the interaction between incident particles in each set of entangled particles, and the subsequent storage of quantum information to quantum memory locations within a quantum repeater, are shown in several embodiments. [Figure 5A] We demonstrate examples of performing Bell state measurements using established pairwise quantum entanglement instances between two quantum repeaters in several embodiments, and extending the quantum entanglement variance based on network demand. [Figure 5B] We demonstrate examples of performing Bell state measurements using established pairwise quantum entanglement instances between two quantum repeaters in several embodiments, and extending the quantum entanglement variance based on network demand. [Figure 5C] We demonstrate examples of performing Bell state measurements using established pairwise quantum entanglement instances between two quantum repeaters in several embodiments, and extending the quantum entanglement variance based on network demand. [Figure 6A] We show examples of maintaining a buffer of established pairwise entanglement instances while one of each pairwise entanglement instance is consumed to extend the entanglement variance, according to several embodiments. [Figure 6B] We show examples of maintaining a buffer of established pairwise entanglement instances while one of each pairwise entanglement instance is consumed to extend the entanglement variance, according to several embodiments. [Figure 6C] We show examples of maintaining a buffer of established pairwise entanglement instances while one of each pairwise entanglement instance is consumed to extend the entanglement variance, according to several embodiments. [Figures 7A-7B]The interactions of a given quantum repeater in a quantum entanglement network are shown in several embodiments, and the given quantum repeater is configured to maintain a buffer of established pairwise quantum entanglement instances with several other quantum repeaters in the quantum entanglement network. [Figure 8A] This flowchart shows the process of maintaining a buffer of established pairwise entanglement instances between two quantum repeaters, according to several embodiments. [Figure 8B] This flowchart illustrates a process that satisfies the requirement of providing endpoint-to-endpoint distributed quantum entanglement according to several embodiments, the process comprising at least utilizing an established pairwise quantum entanglement instance between two intermediate quantum repeater nodes in an endpoint-to-endpoint path across a quantum entanglement network. [Figure 9] This document presents an example of a modular quantum computing system configured to perform multi-qubit gate operations between separate quantum processing units (QPUs) connected via a quantum entanglement network for distributed quantum computation, according to several embodiments. [Figure 10A] This figure shows an example of a quantum circuit including multi-qubit gate operations, according to several embodiments. [Figure 10B] Figure 10A is a flowchart illustrating the process of performing multi-qubit gate operations on the quantum circuit shown in several embodiments, where at least some of the multi-qubit gate operations are performed across the QPU of a modular quantum computing system. [Figure 11] Several embodiments demonstrate an example of performing multi-qubit gate operations across two QPUs in a modular quantum computing system, where the two QPUs are connected across a quantum entanglement network for distributed quantum computing. [Figure 12]We present an example of an elastic quantum computing service that, in several embodiments, allocates a specific number of QPUs connected across a quantum entanglement network used to execute a customer's quantum circuit, and then orchestrates the execution of the quantum circuit using the allocated QPUs. [Figure 13] Further examples of elastic quantum computing services are presented, in several embodiments, that can allocate various combinations of QPUs located in several different quantum hardware facilities for use when executing each quantum circuit. [Figure 14] This flowchart shows the process of executing quantum circuits using modular quantum computing resources of an elastic quantum computing service, according to several embodiments. [Figure 15] This block diagram shows an exemplary classic computing device that may be used in at least some embodiments. [Modes for carrying out the invention]

[0007] Embodiments are described herein as examples of several embodiments and exemplary drawings, but those skilled in the art will recognize that embodiments are not limited to the embodiments or drawings described herein. It should be understood that the drawings and their detailed descriptions are not intended to limit embodiments to any particular form disclosed, but rather to cover all modifications, equivalents, and substitutes that fall within the spirit and scope defined by the appended claims. Headings used herein are for structural purposes only and are not intended to limit the scope of the description or claims. As used throughout this application, the word “may” is used in an acceptable sense (i.e., meaning it is possible) rather than an obligatory sense (i.e., meaning it is a must). Similarly, the words “include,” “including,” and “includes” mean that they include, but are not limited to. Where used in the claims, the term “or” is used in an inclusive sense (i.e., either) rather than an exclusive sense (i.e., either). For example, the phrase “at least one of x, y, or z” means any one of x, y, and z, as well as any combination thereof.

[0008] This disclosure relates to a method and system for providing on-demand distributed quantum entanglement to customers of a distributed quantum entanglement service. By establishing and then maintaining a buffer of pairwise quantum entanglement instances between each quantum repeater node of the quantum entanglement network, the rate at which distributed quantum entanglement can be provided to customers is not limited by the latency of establishing pairwise quantum entanglement instances after receiving a request to provide distributed quantum entanglement. Rather, the established buffer of pairwise quantum entanglement instances may be maintained at any point before receiving a request for distributed quantum entanglement, while providing said distributed quantum entanglement, and after providing said distributed quantum entanglement, so that one or more instances of pairwise quantum entanglement are prepared and consumed as soon as a request for distributed quantum entanglement is received.

[0009] This disclosure also relates to providing distributed quantum computing using a modular quantum computing system. An elastic quantum computing service may be configured to allocate two or more quantum processing units (QPUs) that can be remotely connected via a quantum entanglement network. The allocated two or more QPUs may then be used to execute a given quantum circuit, and the multi-qubit gates of the quantum circuit may be executed across the allocated QPUs via quantum teleportation of the quantum states associated with each multi-qubit gate. In contrast to previously implemented designs of quantum circuit execution using a single QPU, where the quantum computing power was severely limited by the number of physical qubits in a single QPU, distributed quantum computing across multiple QPUs is possible by adapting the overall quantum computing power to meet various performance characteristics and / or needs of the given quantum circuit execution at hand (e.g., circuit depth, type of quantum gate being executed, etc.).

[0010] Figure 1 illustrates the resources of a service provider network that provide quantum entanglement distribution to customer endpoints connected to intermediate quantum repeater nodes in a trust-free region outside of the trusted locations of the service provider network, according to several embodiments.

[0011] In some embodiments, quantum entanglement distribution may include distribution using a plurality of intermediate nodes (e.g., quantum repeaters), and may be used to distribute quantum entanglement to various types of endpoints. In some embodiments, locations outside the trust boundary of service provider network 160 may include intermediate node 120 located in trust-free region 118. Also, in some embodiments, service provider network 160 may further include intermediate node 108. Additionally, in some embodiments, intermediate node 116, which may be included in trusted location 162 or trust-free region 118, may connect service provider network 160 to quantum hardware providers 110, 112, and / or 114 that provide one or more types of quantum computing resources to customers of service provider network 160. For example, quantum hardware providers 110, 112, and 114 may be connected to service provider network 160 via intermediate node 116, and / or connected to other intermediate nodes in trust-free region 118 via intermediate node 116. Additionally, various different customers of the service provider network may be connected such that distributed entanglement may be distributed to various other customers. For example, other customer endpoints 122 and 124 are connected to intermediate node 120 in trust-free region 118.

[0012] In some embodiments, a customer endpoint may have one or more types of endpoint devices. For example, in some embodiments, a customer endpoint may include a fiber-accessible customer endpoint 126 connected to a fiber modem 128 for entanglement measurement. Additionally or alternatively, a customer endpoint may include, for example, a customer quantum device 130 for performing quantum measurements, or may include a full-scale customer quantum computer 132.

[0013] In some embodiments, customer quantum computing device 130 and / or customer quantum computer 132 may further comprise a conversion interface. For example, in some embodiments, the conversion interface may convert a transmission frequency of received particles to a different frequency and / or convert a frequency of outgoing particles to a different frequency. For example, in some embodiments, optical fiber links may transmit photons using different frequency wavelengths, and such variations may be adjusted via the conversion interface of customer quantum computing device 130 and / or customer quantum computer 132.

[0014] In some embodiments, classical computing services of service provider network 160 may be implemented using classical computing resources 102. Also, in some embodiments, quantum computing services may be implemented using quantum computing resources 104 of service provider network 160, or may be implemented using quantum processing units (QPUs) of quantum hardware providers 110, 112, or 114 connected to service provider network 160 via intermediate nodes 108 and / or 116 (as shown in FIG. 1).

[0015] As an example, a customer associated with a fiber-accessible customer endpoint 126 may request entanglement distribution between the fiber-accessible customer endpoint 126 and the service provider network 160 to provide quantum-secure communication between the fiber-accessible customer endpoint 126 and classical computing resources 102 that provide classical computing services to the customer. In response, routing may instruct an intermediate node 134 (which may be an entanglement particle source node) to distribute each particle of the entangled particle pair to the quantum endpoint 106 and the intermediate node 136 (which may be a quantum repeater node). Routing may also instruct an intermediate node 138 (which may be an entanglement particle source node) to distribute each particle of the entangled particle pair to the fiber-accessible customer endpoint 126 and the intermediate node 136 (e.g., a quantum repeater node). Additionally, routing may instruct the intermediate node 136 to perform a joint quantum measurement on the received entangled quantum particles in order to extend the quantum entanglement so that the quantum entanglement is distributed between the quantum endpoint 106 and the fiber-accessible customer endpoint 126. Since the quantum endpoint 106 is located in a trusted location 162 (for example, in a data center with classical computing resources 102), secure communications can be exchanged between the fiber-accessible customer endpoint 126 and the classical computing resources 102 without concern that a third party may intercept or modify the communications as they flow through the trust-free area 118. Similarly, it should be noted that secure communications may be extended to the quantum computing resources 104 and / or QPUs of the quantum hardware providers 110, 112, or 114.

[0016] As shown in Figure 1, it should be noted that a given intermediate node, such as intermediate nodes 120, 134, 108, and 116, may be connected to three or more network links (see also the description of Figures 7A and 7B in this specification). Therefore, routing may select each link to be used for a given intermediate node to form part of a network path from a larger group of network links connected to each intermediate node. In this way, various different network paths for dispersing quantum entanglement may be performed by selecting different combinations of network links from a larger set of network links connected to each of the intermediate nodes.

[0017] In some embodiments, one of the intermediate nodes may introduce a unitary transform that requires the distribution of state information for the receiver to determine whether the measurement results are correlated or inversely correlated. In some embodiments, two or more intermediate nodes may introduce unitary transforms, in which case state information of each introduced unitary transform is required to determine whether the measurement results are correlated or inversely correlated.

[0018] Buffers for pairwise entangled instances for quantum entanglement dispersion Figure 2 shows two quantum repeaters configured, according to several embodiments, to maintain a buffer of established pairwise entangled instances using their respective quantum memory locations within the repeater.

[0019] In some embodiments, quantum repeaters 202 and 204 are analogous to two intermediate nodes in a quantum entanglement network, as in the embodiments shown in Figures 1 and 7A of this specification. Within quantum repeater 202, multiple quantum memory locations can be utilized to provide distributed quantum entanglement services. For example, a given subset of multiple quantum memory locations within the set of quantum memories 204, such as quantum memories 206, 208, 210, 212, 214, 216, 218, 220, 222, and 224, may be designated to receive particles via the optical communication link 200 and then store the corresponding quantum information in each of the set of quantum memories 204. In another example, another given subset of several quantum memory locations within the set of quantum memory 228, such as quantum memories 230, 232, 234, 236, 238, 240, 242, 244, 246, and 248, may be designated to maintain their respective pairwise entangled instances with the quantum memories in another designated set of quantum memory 254 of the quantum repeater 252. According to some embodiments, the size and distribution of the sets of quantum memory 204 and 228 in the entirety of quantum memory locations provided within the quantum repeater 202 may vary according to the expected demand in the quantum entanglement network, meaning that the example shown in Figure 2 is essentially illustrative (see also the description of quantum repeater 708 in Figure 7B of this specification). Next, a Bell state measurement can be performed between any quantum memory location in the set of quantum memory 204 and any quantum memory location in the set of quantum memory 228 using the optical switchboard 226.

[0020] Similar to quantum repeater 252, a given subset of multiple quantum memory locations in the set of quantum memory 278, such as quantum memories 280, 282, 284, 286, 288, 290, 292, 294, 296, and 298, may be designated to receive particles via optical communication link 299 and then store the corresponding quantum information in each of the aforementioned sets of quantum memory 278. In another example, another given subset of multiple quantum memory locations in the set of quantum memory 254, such as quantum memories 256, 258, 260, 262, 264, 266, 268, 270, 272, and 274, may be designated to maintain their respective pairwise entangled instances with the quantum memories in a specified set of quantum memory 228 of quantum repeater 202.

[0021] In some embodiments, a given established pairwise entanglement instance may be referred herein by referring to the corresponding quantum memory location to which the instance relates. For example, at the time shown in Figure 2, six established pairwise entanglement instances are in the established entanglement buffer between quantum repeaters 202 and 252, as shown with respect to quantum memory locations 230 and 256, 232 and 258, 234 and 260, 236 and 262, 238 and 264, and 240 and 266. Furthermore, at the time shown in Figure 2, four additional instances of pairwise entanglement are being attempted between quantum repeaters 202 and 252 (for final establishment), as shown with respect to quantum memory locations 242 and 268, 244 and 270, 246 and 272, and 248 and 274.

[0022] Figure 3 illustrates how quantum entanglement can be extended by performing Bell state measurements between the received particles of each set of entangled particles and the particles in the quantum memory locations of the established pairwise quantum entanglement instances at each quantum repeater location, according to several embodiments.

[0023] In some embodiments, for example, when using quantum repeater 202, joint measurements (e.g., Bell state measurements) may be performed between any one of the quantum memories in set 204 and any one of the quantum memories in set 228, as shown in Figure 3. For example, in step 1, a joint measurement is performed on two particles (e.g., photons) in such a way that the joint measurement only determines whether the two particles are the same or opposite (e.g., whether they are in the same quantum state or not). This is done without revealing any information about the individual particles (e.g., non-destructive measurement). Then, in step 2, the entangled pairs are defined by their correlation, e.g., opposite or identical correlation. In the example shown in Figure 3, both A / B and C / D are entangled such that they are opposite. Then, in step 3, a joint measurement is performed on B / C and the result (e.g., opposite or same) is obtained, which is opposite in the exemplary case shown in Figure 3. This tells A that its complement is the complement of the opposite D, allowing A and D to infer that they are opposite. Next, in step 4, this information is used to entangle the particles such that the A / D particles are always in opposite states. In some embodiments, the joint measurement may be performed using a local two-qubit gate between B and C and using an optical switchboard (e.g., optical switchboard 226 in the example of quantum repeater 202), and may further include measuring each bit individually. This can be understood as an entanglement operation and measurement, or conversely, as a single measurement on an "entangled basis". When the joint measurement is performed in this manner, the result reveals information about the correlation between particles such as particles B and C, but not about the particles themselves. This is due to the entanglement generated by the two-qubit operation. According to some embodiments, such a joint measurement may be performed in a quantum measurement device (see also the messenger quantum measurement device 408 shown in Figure 4), the quantum measurement device may be located within a quantum repeater or directly connected to the components of the quantum repeater, depending on the architecture.

[0024] Figure 4 shows examples of the interaction between incident particles in each set of entangled particles, and the subsequent storage of quantum information into quantum memory locations within a quantum repeater, according to several embodiments.

[0025] In some embodiments, quantum information storage locations within a given quantum repeater (e.g., quantum memories within sets 204 and 228 of quantum memories within quantum repeater 202) may be configured to interact with light, and as a result, the quantum repeater may be configured to receive superposition state photons into on-chip storage.

[0026] In some embodiments, such on-chip storage may be analogous to individual quantum memories, such as a single quantum memory 406, which can be patterned into the quantum information storage 404, as shown in Figure 4. In some embodiments, the quantum information storage 404 may be configured to couple with photonic waveguides 410 and 412 to receive incident photons. The quantum information storage 404 may then be configured to capture light through through-holes shown in Figure 4, which can function as mirrors, according to some embodiments. In some embodiments, the quantum memory patterned into the quantum information storage 404 may include nanophotonic cavities, such as nanophotonic cavities shown in a single quantum memory 404 exhibiting silicon vacancies in a diamond structure. In such embodiments, the silicon vacancies are embedded within nanophotonic cavities in a bulk substrate material, in which case the bulk substrate material may be diamond. The silicon vacancies in a diamond structure, such as the single quantum memory 404, can function as quantum memory storage, and the corresponding nanophotonic cavities (e.g., through-holes patterned in diamond) can allow light to interface with the silicon vacancies in the diamond structure. However, in other embodiments, quantum memories may be analogous to other internal features embedded in a material, such as nitrogen vacancies, trapped atoms, ensemble-doped crystals, atomic vapors, silicon carbide emitters, single rare-earth dopants, trapped ions, superconducting qubits, quantum dots in gallium arsenide, or defect centers in silicon or other semiconductor materials.

[0027] In some embodiments, quantum memory can provide a method for receiving, storing, and providing quantum information. In some cases, quantum memory devices may be deployed for use in large-scale optical fiber networks and / or quantum entanglement networks, for example, as quantum repeaters, to store and effectively connect dispersed entangled particles in order to provide secure long-distance communication. In such applications, as shown in Figure 4, a quantum memory implemented in a quantum repeater can function such that the tuning of the quantum memory (e.g., single quantum memory 406) (e.g., adjustment to local electrical, optical, thermal, and electromechanical environments) can be contained and controlled within a given quantum repeater.

[0028] In some embodiments, quantum memory-based architectures, such as those shown in Figure 2, which include a quantum information storage device, may be similar to those depicted in Figure 4. As further shown in Figure 4, the input interface 402 may be configured to receive superposition-state particles into a quantum information storage 404 comprising a single quantum memory 406, and may be configured to be coupled to a messenger quantum measurement device 408 via a photonic waveguide layer 412. For example, the single quantum memory 406 represents silicon vacancies in a diamond structure. However, in some embodiments, other structures may be used, such as nitrogen vacancies in diamond, trapped atoms, ensemble-doped crystals, atomic vapors, silicon carbide emitters, single rare-earth dopants, trapped ions, superconducting qubits, and quantum dots in gallium arsenide. Furthermore, while the input interface 402 shows one embodiment of a time-bin-qubit coding-transformation module, other embodiments with other input interface configurations, including wavelength or mode matching, may be used.

[0029] In some embodiments, the input interface 402 may be configured to couple with a photonic waveguide layer 410. The photonic waveguide layer 410 may be a material that can be patterned such that optical waveguides can be formed within the material (e.g., silicon nitride, lithium niobate, aluminum nitride, etc.). It may further be optically transparent in one or more given wavelength ranges (e.g., the visible light spectrum) and may have nonlinear optical and / or electro-optic properties. The photonic waveguide layer 412 may be a material manufactured from a bulk substrate via the manufacturing processes and methods described herein and, according to some embodiments, may be configured to host an optically active quantum memory (e.g., a single quantum memory 406) in a photonic cavity described by the quantum information storage 404.

[0030] In some embodiments, a given quantum repeater having the architectural components shown in Figure 4 can be configured to store quantum information corresponding to the first received entangled particle of a first pair of entangled particles in a first single quantum memory 406 of the quantum information storage 404, and also to store quantum information corresponding to the second received entangled particle of a second pair of entangled particles in a second single quantum memory 406 of the quantum information storage 404 (for example, using set 204 and set 228 of quantum memories when using quantum repeater 202 as an example). The given components of the quantum repeater architecture shown in Figure 4 can be further configured to perform one or more joint measurements (e.g., Bell state measurements) using the quantum information storage locations without disrupting the superposition state of the first and second entangled particles (e.g., non-destructive measurement) by routing to a messenger quantum measurement device 408 using an optical switchboard. The collaborative measurement can determine the correlation between the superposition states of entangled particles, and as a result, the entanglement can be extended between pairs of entangled particles.

[0031] In some embodiments, a given quantum repeater architecture may be configured to messenger particle reception, meaning that when a particle arrives at a given quantum repeater, a quantum measurement device 408 (or another device coupled to the quantum information storage 404) issues a messenger signal to indicate the arrival of the particle. In some embodiments, such a messenger signal may be used to operate an optical switch to align the switch so that a quantum memory receives the next particle from the entangled particle source from which the quantum entanglement will be dispersed. Furthermore, when a second particle arrives at the quantum repeater, a second messenger signal may be issued. The second messenger signal can then be used to perform a joint measurement. With respect to the description herein of maintaining a buffer of established pairwise quantum entanglement instances, one or more pairwise quantum entanglement instances are prepared and ready for such on-demand quantum entanglement dispersion, so there is no need to wait for a messenger signal for the arrival of a second particle.

[0032] Furthermore, co-measurements can be used to at least partially extend the entanglement between two endpoints of a quantum entanglement network. In some embodiments, a device such as the one shown in Figure 4 can perform messenger and co-measurements, or in some embodiments, different quantum measurement devices 408 can be used to perform messenger and co-measurements on a received particle pair. In some embodiments, the messenger function may be performed by a quantum non-destructive measurement device that can detect particles (e.g., photons) entering the quantum repeater without causing the particles to collapse from a superposition state.

[0033] In some embodiments, the quantum repeater may further include a conversion interface. For example, in some embodiments, the conversion interface can convert the transmission frequency of the received particle to a different frequency. For example, in some embodiments, an optical fiber link can transmit particles using different frequency wavelengths, and such variations can be regulated via the conversion interface of the quantum repeater.

[0034] In some embodiments, a quantum repeater, such as those described herein, may further include optical fiber ports and / or electrical ports that provide access points between optical fiber cables, control signal leads, wires, electrical cables, etc., located outside the quantum repeater and various components within the quantum repeater.

[0035] Figures 5A to 5C illustrate examples of performing Bell state measurements using established pairwise quantum entanglement instances between two quantum repeaters, and extending the quantum entanglement dispersion based on network demand, in several embodiments.

[0036] At a given time point shown in Figure 5A, there are six established pairwise entanglement instances within the established quantum entanglement buffer between quantum repeaters 502 and 512 connected via optical communication link 510.

[0037] As shown in the figure, at the aforementioned point in time, the quantum repeaters 502 and 512 may not be active as part of the request to provide distributed quantum entanglement, as evidenced by the empty quantum memory locations in the set of quantum memories 504 and the set of quantum memories 518.

[0038] As shown in Figure 5B, at a later point in time, it may be in the process of providing endpoint-to-endpoint distributed quantum entanglement between customer Alice's endpoint and customer Bob's endpoint. Since quantum repeaters 502 and 518 can be configured to be part of the entire optical communication path for providing the endpoint-to-endpoint distributed quantum entanglement, according to some embodiments, one of the six already established pairwise quantum entanglement instances of the buffer shown in Figure 5B, for example, the established pairwise quantum entanglement instance between quantum memory locations 526 and 528, can be allocated for consumption.

[0039] After receiving entangled particles via optical communication link 500 to quantum repeater 502 that share entanglement with particles received at customer Alice's endpoint, and storing the corresponding quantum information in quantum memory location 522, a Bell state measurement 524 can be performed between quantum memory locations 522 and 526 using optical switchboard 506. Similarly, after receiving different entangled particles via optical communication link 520 to quantum repeater 512 that share entanglement with particles received at customer Bob's endpoint, and storing the corresponding quantum information in quantum memory location 532, a Bell state measurement 530 can be performed between quantum memory locations 528 and 532 using optical switchboard 516.

[0040] As illustrated using the depictions in Figures 5A, 5B, and 5C, an established pairwise entanglement instance between quantum repeaters 502 and 512 may be applied to provide distributed entanglement between customer Alice and customer Bob, thereby ensuring an on-demand entanglement service. Furthermore, based on the routing flexibility provided by the respective optical switchboards on the quantum repeaters, another established pairwise entanglement instance of the buffer can be used to further provide distributed entanglement to another set of customers, as shown in Figure 5C.

[0041] As shown in Figure 5C, at a point later than the time shown in Figure 5B, the entangled quantum instances between quantum memory locations 526 and 528 are consumed in order to provide distributed quantum entanglement to customers Alice and Bob. Next, in order to maintain the buffer of established pairwise entangled quantum instances between quantum repeaters 502 and 512, an attempt is made to re-establish new entangled quantum instances using the available quantum memory locations in each quantum repeater.

[0042] Furthermore, the time point shown in Figure 5C may be similar to another time point in which the provision of distributed quantum entanglement is similarly underway using at least quantum repeaters 502 and 512. As described above with respect to Figure 5B, according to some embodiments, one of the already established pairwise quantum entanglement instances of the buffer shown in Figure 5C, for example, the established pairwise quantum entanglement instance between quantum memory locations 540 and 542, may be allocated for consumption. Thus, after receiving entangled particles that share entanglement with particles received at other customer endpoints via the optical communication link 534 into quantum repeater 502 and storing the corresponding quantum information in quantum memory location 536, a Bell state measurement 538 can be performed between quantum memory locations 536 and 540 using the optical switchboard 506. Similarly, by receiving different entangled particles via optical communication link 548 to quantum repeater 512 that share entanglement with a particle received by another quantum repeater in the quantum entanglement network, and storing the corresponding quantum information in quantum memory location 546, a Bell state measurement 544 can be performed between quantum memory locations 542 and 546 using optical switchboard 516.

[0043] Figures 6A to 6C illustrate examples of maintaining a buffer of established pairwise entanglement instances while one of each pairwise entanglement instances is consumed to extend the entanglement dispersion, according to several embodiments.

[0044] In some embodiments, Figures 6A–6C show three points in time, relative to the time shown in Figure 6A, where various established pairwise entangled instances of the buffer between quantum repeaters 602 and 632 are consumed to provide distributed entanglement. In order to maintain the buffer of established pairwise entangled instances between quantum repeaters 602 and 632, the establishment of entanglement may be retried and re-established following an event relating to the consumption of a given pairwise entangled instance in the buffer. In some embodiments, Figures 6A–6C can also show three points in time, relative to the time shown in Figure 6A, where various established pairwise entangled instances of the buffer have decayed, at least partially due to the coherence time of the qubits associated with each quantum memory location of the quantum repeaters shown in Figures 6A–6C.

[0045] At the point in time shown in Figure 6A (for example, time step 1), there are six established pairwise entangled instances in the buffer of established pairwise entangled instances between quantum repeaters 602 and 612, as shown between quantum memory locations 610 and 636, 612 and 638, 614 and 640, 616 and 642, 618 and 644, and 620 and 646. As further shown in the figure, quantum entanglement is currently being attempted between quantum memory locations 622 and 648, 624 and 650, 626 and 652, and 628 and 654.

[0046] At a later point in time (e.g., timestep 2) shown in Figure 6B, there are five established pairwise entangled instances within the buffer of established pairwise entangled instances between quantum repeaters 602 and 612, as shown between quantum memory locations 610 and 636, 612 and 638, 614 and 640, 616 and 642, and 618 and 644. Between the moment shown in Figure 6A and the later moment shown in Figure 6B, the instance between quantum memory locations 620 and 646 may have been consumed to provide distributed entanglement, or it may have decayed due to the elapsed time between the establishment of the instance and the duration of the coherence time of the qubits corresponding to quantum memory locations 620 and 646.

[0047] At a later point in time (e.g., time step 3) shown in Figure 6C, there are seven established pairwise entangled instances in the buffer of established pairwise entangled instances between quantum repeaters 602 and 612, as shown between quantum memory locations 612 and 638, 614 and 640, 616 and 642, 618 and 644, 624 and 650, 626 and 652, and 628 and 654. Between the moment shown in Figure 6B and the later moment shown in Figure 6C, the instance between quantum memory locations 610 and 636 may have been consumed to provide distributed entanglement, or it may have decayed due to the elapsed time between the establishment of the instance and the duration of the coherence time of the qubits corresponding to quantum memory locations 610 and 636. Furthermore, additional pairwise entanglement instances are established between the time point shown in Figure 6B and the later time point shown in Figure 6C, and form part of the buffer of established pairwise entanglement instances between quantum repeaters 602 and 612, as shown between quantum memory locations 624 and 650, between 626 and 652, and between 628 and 654.

[0048] Furthermore, as further illustrated using the examples provided in Figures 6A-6C of this specification, the buffer of established pairwise entangled quantum entanglement instances between quantum repeaters 602 and 632 may be continuously maintained to provide distributed quantum entanglement to customers (for example, as shown via empty quantum memory locations in the set of quantum memories 604 and set of quantum memories 658 shown in the figures) even when quantum repeaters 602 and 632 are not being used at the time shown in Figures 6A-6C. Thus, on-demand distributed quantum entanglement may be provided without the latency resulting from establishing entangled quantum entanglement instances after receiving a request to provide distributed quantum entanglement, even if a subsequent request is received at a later time.

[0049] Figures 7A and 7B illustrate the interaction of a given quantum repeater in a quantum entanglement network according to several embodiments, where the given quantum repeater is configured to maintain a buffer of established pairwise entanglement instances with several other quantum repeaters in the quantum entanglement network.

[0050] In some embodiments, as shown in Figures 7A and 7B, the quantum repeater 708 may be configured to maintain multiple buffers of established pairwise quantum entanglement instances with each other quantum repeater in the quantum entanglement network 700. Customer endpoints 702 and 710, as well as quantum repeaters 704, 706, 708, 712, and 714, are intended for illustrative purposes only, and embodiments such as those shown in Figure 7A can be similarly described with respect to the embodiments shown in Figure 1 and described herein.

[0051] As shown in Figures 7A and 7B, the quantum repeater 708 may be configured such that a logically designated set of quantum memories within the total number of quantum memory locations provided within the quantum repeater 708 can be allocated for interaction between the quantum repeater 708 and other different quantum repeaters and / or customer endpoints in the quantum entanglement network 700, depending on a given arrangement of the quantum repeater 708 in a larger network. For example, quantum memory locations 754, 756, and 758 in quantum memory set 752 may be designated for receiving entangled particles with customer 2's endpoint 710, quantum memory locations 762, 764, and 766 in quantum memory set 760 may be designated for establishing and maintaining a buffer of established pairwise quantum entanglement instances between quantum repeater 708 and quantum repeater 704, and quantum memory locations 770, 772, 774, and 776 in quantum memory set 768 may also be designated for established pairwise quantum between quantum repeater 708 and quantum repeater 706. Quantum memory locations 782, 784, 786, and 788 in the quantum memory set 780 may be designated to establish and maintain yet another buffer of the established pairwise entangled instance between quantum repeater 708 and quantum repeater 712, and quantum memory locations 792, 794, 796, and 798 in the quantum memory set 790 may be designated to establish and maintain yet another buffer of the established pairwise entangled instance between quantum repeater 708 and quantum repeater 714.

[0052] In some embodiments, each quantum memory location within the quantum memory sets 752, 760, 768, 780, and 790 can be used to perform Bell state measurements with any of the other quantum memory locations within the quantum memory sets 752, 760, 768, 780, and 790 via a single optical switchboard 778.

[0053] Furthermore, the quantum memory sets 752, 760, 768, 780, and 790 can represent logical designations for various quantum memory locations within the quantum repeater 708, as shown in Figure 7B, and any quantum memory location in a given set of quantum memory can be reallocated to another set of quantum memory within the quantum repeater to provide more optimized on-demand distributed quantum entanglement within the quantum entanglement network 700. For example, if, over a given period, the consumption rate of instances in a buffer of established pairwise entangled instances between quantum repeaters 708 and 704 appears to be higher than the consumption rate of instances in another buffer of established pairwise entangled instances between quantum repeaters 708 and 706, then one or more quantum memory locations in the quantum memory set 768 may be logically reallocated to the quantum memory set 760. Since the optical switchboard 778 can still route between the quantum memory locations, such logical reassignments can provide further flexibility to the architecture described with respect to the quantum repeater 708 without incurring additional latency when providing on-demand distributed quantum entanglement.

[0054] Figure 8A is a flowchart illustrating the process of maintaining a buffer of established pairwise entanglement instances between two quantum repeaters, according to several embodiments.

[0055] In some embodiments, a buffer of pairwise entangled instances can be established, as described in block 800, and then repeatedly maintained over time, as described in blocks 802 and 804, to provide on-demand distributed entanglement to entangled networks as illustrated and described with respect to Figures 1 to 7B. Blocks 800, 802, and 804 can represent a kind of continuous loop used to ensure that the buffer is maintained even through events such as the decay and / or consumption of one of the established pairwise entangled instances in the buffer. Furthermore, according to some embodiments, the repeating loop described by blocks 800, 802, and 804 can continue to cycle and maintain the established buffer of pairwise entanglement even when there are currently no pending and / or incoming requests to provide distributed entanglement (see also the description of block 850).

[0056] Following the establishment of the buffer described in block 800, block 802 can refer to a process of iteratively monitoring the consumption of various pairwise entanglement instances within the buffer, according to some embodiments. For example, as further described herein with respect to Figures 5A–6C, each pairwise entanglement instance may be used when performing Bell state measurements to provide endpoint-to-endpoint distributed entanglement, causing the instance in the buffer to be consumed. Once the consumption of a given pairwise entanglement instance in the buffer is detected and / or registered, the pairwise entanglement can be retried and then re-established in order to maintain the buffer of established pairwise entanglement instances.

[0057] In some embodiments, block 802 may also refer to a process of repeatedly re-establishing each pairwise entangled instance following a decay event of a previously established pairwise entangled instance in the buffer. For example, a given pairwise entangled instance may decay after a given period defined at least partially by the coherence time of the qubit associated with the quantum memory location corresponding to the instance. Thus, block 804 may refer to a component of the loop shown in Figure 8A, where an evaluation is performed between when a given instance of the buffer was established (e.g., time t0) and a time elapsed since time t0 (e.g., time period t0→t1). If the period defined by t0→t1 is greater than the known coherence time of the associated qubit in the quantum memory location defining a given pairwise entangled instance, the system determines that a particular instance has decayed and attempts to re-establish another pairwise entangled instance in order to maintain the buffer of established pairwise entangled instances.

[0058] By monitoring the state of established pairwise entangled instances in the buffer (e.g., an instance is currently established and therefore represents ongoing entanglement, an instance has decayed, an instance has been consumed to provide distributed entanglement, an instance is currently in the process of retrying to establish pairwise entanglement, etc.), it is possible to attempt and re-establish entanglement on demand and without latency to satisfy requests to provide distributed entanglement, following the decay and / or consumption of each instance.

[0059] Figure 8B is a flowchart illustrating a process that satisfies the requirement of providing endpoint-to-endpoint distributed quantum entanglement according to several embodiments, the process comprising at least utilizing an established pairwise quantum entanglement instance between two intermediate quantum repeater nodes in an endpoint-to-endpoint path across a quantum entanglement network.

[0060] In some embodiments, a request to provide endpoint-to-endpoint distributed quantum entanglement may be received, as shown in block 850. Furthermore, a given optical communication path defining the endpoint-to-endpoint may include at least two quantum repeater locations where established pairwise quantum entanglement instances are already prepared and ready for on-demand quantum entanglement distribution. For example, a given optical communication path that can be used to provide endpoint-to-endpoint distributed quantum entanglement may be similar to one of the given route options shown in the quantum entanglement network 700 in Figure 7A, and may include route points at customer 1's endpoint 702, quantum repeater 704, quantum repeater 708, and customer 2's endpoint 710, as further shown in Figure 7A. Therefore, at a given junction between two quantum repeaters in an endpoint-to-endpoint optical communication path (e.g., the junction between quantum repeaters 704 and 708), a given established pairwise entanglement instance of the buffer may be used when performing Bell state measurements at the locations of the first and second quantum repeaters at the given junction, as described in blocks 852, 854, and 858. The results of the respective Bell state measurements may then be provided, as described in blocks 856 and 860, to provide dispersed quantum entanglement between customer 1's endpoint 702 and customer 2's endpoint 710.

[0061] Modular quantum computing systems for distributed quantum computing Figure 9 shows an example of a modular quantum computing system configured to perform multi-qubit gate operations between separate quantum processing units (QPUs) connected via a quantum entanglement network for distributed quantum computation, according to several embodiments.

[0062] In some embodiments, methods for providing quantum entanglement dispersion, as described herein, may also be applied to running quantum circuits using QPUs in a modular quantum computing system. As shown in Figure 9, the modular quantum computing system 900 includes QPUs 902 and 390 which may be remotely connected using an optical communication link 916 (e.g., a link established over optical fiber) of the quantum entanglement network 932.

[0063] For the purposes of this specification, a quantum circuit can refer to the execution of one or more quantum gates using the physical qubits of a QPU. An example of a quantum circuit is further described herein with respect to quantum circuit 1000 in Figure 10A. Furthermore, a quantum circuit can refer to a “basic unit” to another phrase that describes a quantum algorithm, a quantum task, a quantum program, or a group of two or more quantum circuits in which the input to a second quantum circuit may depend on the result of a first quantum circuit within a given quantum algorithm.

[0064] Furthermore, in connection with the description herein, it can be understood that quantum hardware may be used to implement the QPU and / or various components of the QPU (e.g., quantum processing cores, routing spaces, magic state distillation factories, other components used to perform logical quantum computations, etc.). For example, a given quantum hardware device may be analogous to the "building blocks" of the QPU, such as a grid of qubits (e.g., a one-dimensional grid, a two-dimensional grid, etc.) which can be initialized in various ways to form various components of the QPU, such as a topological quantum code. The quantum hardware device may be further configured so that single-qubit gates, multi-qubit gates, and / or other operations of quantum circuits can be performed between the qubits of the QPU (according to a given physical qubit connection graph of the QPU detailing which physical qubits are connected to each other physical qubits via edges).

[0065] In some embodiments, depending on factors such as the type of qubit technology used and the type of gates executed between the qubits, the quantum hardware device implementing the QPU may also include various control devices (e.g., microwave pulse generators, devices for temperature, electronic, magnetic, and / or other environmental control or combination thereof related to the local environment of the qubit grid) that can be used to maintain and / or transform various properties of the qubits and / or other physical components of a given QPU. Furthermore, a qubit can refer to both a logic bit (e.g., a first or second superposition state, each having a certain probability) and one or more physical components used to construct a given qubit, at least in part on the type of qubit technology applied. For example, a superconducting qubit (e.g., a transmon) may be constructed using at least sections of a material known to have certain superconducting properties and another material. In relation to this understanding, it should also be understood that quantum hardware can be used to implement physical qubits in the manner described above, so that logical quantum operations can be performed using the physical elements of the quantum hardware, and can therefore be combined again in various ways to implement one or more logical qubits.

[0066] As shown in Figure 9, QPU902 and 930 can include physical qubits, with one of each physical qubit connected to the others. For example, QPU902 includes five physical qubits {q1, q2, q3, q4, q5}, where physical qubits q1 and q2 are physically connected via edge e1, physical qubits q2 and q3 are physically connected via edge e2, physical qubits q2 and q4 are physically connected via edge e3, and physical qubits q4 and q5 are physically connected via edge e4. Furthermore, QPU930 includes four physical qubits {q1, q2, q3, q4}, where physical qubits q1 and q3 are physically connected via edge e1, physical qubits q2 and q3 are physically connected via edge e2, and physical qubits q3 and q4 are physically connected via edge e3.

[0067] As further shown in Figure 9, at least one physical qubit of the QPU902 is designated for quantum computation operations (e.g., qubits q1, q2, and q3), and at least one physical qubit is designated for quantum entanglement operations (e.g., qubits q4 and q5). As indicated by the “Key” in Figure 9, the darker and brighter shading on the physical qubits designated for quantum entanglement operations correspond to the above descriptions of the qubits used for established pairwise entangled instances in the buffer and the qubits used to generate pairwise entangled instances added to the buffer, respectively, at different points in time (see also the description relating to at least Figure 2 in this specification). Similar physical qubit designations may also apply to the QPU930, as also shown in Figure 9.

[0068] Furthermore, the examples of QPUs such as QPU902 and 930 are intended to be illustrative in nature, and the description herein is intended to encompass additional embodiments of QPUs having more or fewer physical qubits than those shown in Figure 9, and / or QPUs having alternative physical qubit connectivity configurations. Furthermore, the designation of specific physical qubits for quantum computation and / or quantum entanglement operations may refer to logical designations. Moreover, such designations may be configured at least in part on the respective physical qubit connectivity of the corresponding QPUs.

[0069] In some embodiments, to perform distributed quantum computing, the modular quantum computing system 900 may further include various optical interfaces configured to enable transduction of quantum information between a given qubit-technical grouping type of physical qubit (e.g., superconducting qubits) used to implement a QPU 902 or 930 and a set of quantum memories used to establish and maintain pairwise entanglement instances. For example, in some embodiments in which the QPU 902 is implemented using superconducting qubits, an optical transducer 904 may be connected to the physical qubits q4 and q5 of the QPU 902 designated for quantum entanglement to provide transduction of quantum information for an optical switchboard 906 between the microwave frequencies of operation in the physical qubits q4 and q5 of the QPU 902 and the optical frequencies of operation in the set of quantum memories 908. Similarly, an optical interface 926 may provide similar transduction of quantum information for an optical switchboard 928, depending on the qubit-technical grouping of the physical qubits q1 and q2 of the QPU 930.

[0070] Furthermore, as described above with respect to Figures 2 to 8B, quantum memories 910, 912, and 914 in the quantum memory set 908, and quantum memories 920, 922, and 924 in the quantum memory set 918, may be used to provide a buffer of established pairwise entangled instances via the optical communication link 916 for performing distributed quantum computations for the modular quantum computing system 900. Each pairwise entangled instance may be established among various combinations of memory locations 910, 912, 914, 920, 922, and 924 so that the buffer of established pairwise entangled instances is maintained both before and during the execution of a given quantum circuit using the modular quantum computing system 900. According to some embodiments, the size of the buffer may depend on the demand for performing distributed quantum computations using the modular quantum computing system 900 at a given time.

[0071] Figure 10A shows an example of a quantum circuit including multi-qubit gate operations, and Figure 10B is a flowchart illustrating the process of performing multi-qubit gate operations of the quantum circuit shown in Figure 10A in several embodiments, where at least some of the multi-qubit gate operations are performed across the QPU of a modular quantum computing system.

[0072] As described above, the quantum circuit 1000 may include one or more quantum gates {g1, g2, g3, g4} executed between logic qubits {A, B, C, D, E}. In some embodiments, the quantum circuit 1000 can be represented by a high-level circuit diagram that describes relevant information such as circuit depth and gate dependencies. For example, according to the quantum circuit 1000 shown in Figure 10A, quantum gate g1 must be executed using logic qubit B before gate g4 can be executed for logic qubit B. In some embodiments, the gate dependency list of the quantum circuit 1000 may be similar to the following: {(A),(B),(C),(D),(E)}={(g1,…),(g1,g4,…),(g3,g4,…),(g2,g3,…),(g2,…)}.

[0073] In some embodiments, the modular quantum computing system 900 may be configured to execute a quantum circuit 1000 using physical qubits of QPUs 902 and 930. To execute the quantum circuit 1000, an elastic quantum computing service, such as those further described herein with reference to Figures 12, 13, and 14, can determine gate scheduling instructions to be applied during the execution of the quantum circuit 1000. The gate scheduling instructions may include scheduling one or more quantum gates to be executed using physical qubits of QPU 902 designated for quantum computation, scheduling one or more quantum gates to be executed using physical qubits of QPU 930 designated for quantum computation, and scheduling at least one multi-qubit quantum gate to be executed using physical qubits of QPU 902 and QPU 930 designated for quantum computation.

[0074] Furthermore, determining the gate scheduling instructions may further include additional preprocessing steps before initiating the execution of the quantum circuit 1000, such as a mapping step from logical qubits to (one or more) physical qubits, where one of each of the logical qubits {A, B, C, D, E} can be mapped to a physical qubit of the modular quantum computing system 900 in order to determine a path based on the physical qubit connectivity of different QPUs to execute the quantum gates {g1, g2, g3, g4}. For example, the five logical qubits of the quantum circuit 1000 may be mapped one-to-one to five physical qubits designated for quantum computation within the modular quantum computing system 900 (e.g., qubits q1, q2, and q3 of QPU 902, and qubits q3 and q4 of QPU 930). Additional exemplary mapping schemes may include mapping one logical qubit to one or more physical qubits, depending on the specific QPU of the modular quantum computing system used to execute a given quantum circuit. Furthermore, such a mapping step from logical qubits to physical qubits can be additionally used to determine the minimum number of physical qubits expected to be needed to run the quantum circuit 1000. Continuing with the example of running the quantum circuit 1000 using the modular quantum computing system 900, according to some embodiments, the minimum number of physical qubits expected to be needed to run the quantum circuit 1000 may be determined to be less than or equal to the total number of physical qubits available across QPUs 902 and 930. This type of preprocessing step will be further described with respect to elastic quantum computing services as shown in Figures 12 and 13 of this specification.

[0075] In some embodiments, the flowchart shown in Figure 10B can provide an exemplary representation of such gate scheduling instructions determined by the elastic quantum computing service. As shown in block 1050, the resulting gate scheduling instructions can determine that quantum gate g1 may be executed between physical qubits in QPU 902. As shown in block 1052, quantum gate g2 may be executed between physical qubits in QPU 930. In some embodiments, the execution of quantum gate q1 may be performed independently of quantum gate g2 (for example, quantum gate q1 may be executed without depending on the result of quantum gate g2, and vice versa), so gate scheduling instructions such as those shown in blocks 1050 and 1052 may be executed sequentially or in parallel with each other.

[0076] Continuing with such exemplary gate scheduling instructions, block 1054 explains that quantum gate g3 may be executed using a given physical qubit from the physical qubits designated for quantum computation in QPU 902 and a given physical qubit from the physical qubits designated for quantum computation in QPU 930. Further explanation of the execution of multi-qubit gates as described in block 1054 is provided with respect to Figure 11 of this specification. Furthermore, as stated above with respect to the gate dependency list, since quantum gate g3 depends on the result of quantum gate g2, quantum gate g3 in block 1054 is executed at least sequentially after the execution of quantum gate g2. Next, in block 1056, quantum gate g4 and any subsequent gates of quantum circuit 1000 may be executed using various combinations of physical qubits designated for quantum computation in QPU 902 and / or 930.

[0077] As illustrated by at least the examples in Figures 10A and 10B, the modular quantum computing system 900 may be configured to perform various quantum computation operations across multiple QPUs remotely connected via established pairwise quantum entanglement instances, the various quantum computation operations being located within a given quantum circuit (for example, at the “base unit” level with respect to larger quantum computations such as quantum algorithms and programs, as further described above).

[0078] Figure 11 shows an example of performing multi-qubit gate operations across two QPUs in a modular quantum computing system, according to several embodiments, where the two QPUs are connected across a quantum entanglement network for distributed quantum computing.

[0079] In some embodiments, the modular quantum computing system 1100 may be similar to an embodiment of the modular quantum computing system 900, which is configured to perform distributed quantum computation using two or more QPUs remotely connected via an established pairwise quantum entanglement instance. At the point shown in Figure 11, a multi-qubit quantum gate is being executed between the physical qubit 1104 of QPU 1102 and the physical qubit 1146 of QPU 1138. As further shown in Figure 11, a given pairwise entangled instance of the buffer is used to teleport the quantum state between physical qubit 1104 and physical qubit 1146, as depicted across qubits 1108, 1120, 1130, and 1142 in the figure, while additional pairwise entangled instances of the buffer, as depicted across qubits 1106, 1118, 1128, and 1140, and across qubits 1110, 1122, 1132, and 1144 in the figure, represent established pairwise entangled instances that can be used for subsequent multi-qubit gates of a given quantum circuit currently running at the time shown in Figure 11.

[0080] In some embodiments, the quantum entanglement can be distributed from physical qubit 1108 to quantum memory location 1130 across optical communication link 1124, and across physical qubit 1142 via optical converter 1136, using a given established pairwise quantum entanglement instance currently consumed to teleport the quantum state between physical qubit 1104 and physical qubit 1146. This distribution can interface with quantum memory location 1120 via optical converter 1114. As described above with respect to Figures 2 to 10B, Bell state measurements can be performed, and optical switchboards 1114 and 1134 route between various quantum memory locations of the quantum memory sets 1116 and 1126 and the physical qubits designated for the quantum entanglement in QPUs 1102 and 1138.

[0081] In some embodiments, one or more SWAP gate operations can be performed between each of the physical qubits designated for quantum computation in the QPU 1102, as shown by the given quantum logic operation path in Figure 11, to transfer the quantum state of physical qubit 1104 to physical qubit 1108 for the teleportation of the quantum information over optical communication link 1124. Such a path may depend on the physical qubit connectivity of the QPU 1102, as further described with respect to Figure 9 of this specification. According to some embodiments, similar SWAP gate operations may be performed to transfer quantum states between physical qubits 1142 and 1146 of the QPU 1138.

[0082] Elastic quantum computing service for distributed quantum computing Figure 12 illustrates examples of interactions between various quantum hardware devices in an elastic quantum computing service, which, in several embodiments, allocates a specific number of QPUs connected across a quantum entanglement network used to execute a customer's quantum circuit, and then orchestrates the execution of the quantum circuit using the allocated QPUs.

[0083] Quantum computers are difficult to build and operate, and can be costly. Furthermore, while various quantum computing technologies are under development, there is no clear trend regarding which of these technologies will become prominent. Those skilled in the art can relate such current obstacles facing the scientific community to the NISQ hardware phase within the overall development, operation, and optimization of various quantum computing technologies. Therefore, potential quantum computer users may hesitate to invest in building or acquiring a particular type of quantum computer, as other quantum computing technologies may overshadow the select quantum computing technologies they may be interested in. Additionally, successfully using quantum computers to solve practical problems may require considerable trial and error and / or significant expertise otherwise.

[0084] As an alternative to building and maintaining a quantum computer, potential users of quantum computers may prefer to rely on quantum computing services to provide access to them. Furthermore, in some embodiments, elastic quantum computing services, such as those described herein, may enable potential users of quantum computers to access them based on multiple different quantum computing technologies and / or paradigms without the costs and resources required to build or manage such a quantum computer. Also, in some embodiments, elastic quantum computing services described herein can provide a variety of services that simplify the quantum computing experience, enabling potential quantum computer users who lack deep experience or knowledge of quantum mechanics to nevertheless utilize the quantum computing services to solve problems.

[0085] In some embodiments, the elastic quantum computing service can provide potential quantum computing users with access to QPUs (e.g., QPU1264, 1278, and 1290) implemented using various quantum computing techniques such as quantum annealers, ion trap machines, superconducting machines, Rydberg atomic arrays, and photonic devices. In some embodiments, the quantum computing service can provide customers with access to at least three broad categories of quantum computers, including quantum annealers, circuit-based quantum computers, and analog or continuously variable quantum computers. As used herein, these three broad categories may be referred to as quantum computing paradigms.

[0086] In some embodiments, the elastic quantum computing service can provide access to a total of several QPUs that can be allocated and used to execute various quantum circuits. For example, QPUs 1264, 1278, and 1290 may currently be allocated to execute a given quantum circuit, such as quantum circuit 1000. At a later point in time, QPUs 1264 and 1278 may be reallocated to execute different quantum circuits, and QPU 1290 and various other QPUs made accessible by the elastic quantum computing service may be reallocated to execute yet another quantum circuit, etc. The elastic quantum computing service may be configured to provide increased quantum computing power by allocating multiple QPUs used to execute a given quantum circuit, at least in part on the performance characteristics of the quantum circuit (e.g., the depth of the circuit, the type of quantum gates executed, etc.) and on the demand within the overall service at a given point in time. Furthermore, by enabling multiple QPUs to be allocated to execute a given quantum circuit, the quantum computing power can be greater than when only a single QPU is allocated to execute the quantum circuit.

[0087] As shown in Figure 12, a given multi-qubit gate of a currently running quantum circuit can include the teleportation of quantum states between physical qubit 1262 of QPU 1264 and physical qubit 1286 of QPU 1290. As described above with respect to the modular quantum computing system 1100, various SWAP gate operations can be performed between qubits 1262 and 1254, and between qubits 1286 and 1280, to transfer quantum states between physical qubits designated for quantum computation and physical qubits designated for quantum entanglement, respectively.

[0088] In another example, another multi-qubit gate in the currently running quantum circuit may include the teleportation of quantum states between physical qubit 1260 of QPU1264 and physical qubit 1274 of QPU1278. As described above with respect to the modular quantum computing system 1100, various SWAP gate operations can be performed between qubits 1260 and 1256, and between qubits 1274 and 1268, to transfer quantum states between physical qubits designated for quantum computation and physical qubits designated for quantum entanglement, respectively.

[0089] In yet another example, further multi-qubit gates in the currently running quantum circuit may include the teleportation of quantum states between physical qubit 1276 of QPU1278 and physical qubit 1288 of QPU1290. As described above with respect to the modular quantum computing system 1100, various SWAP gate operations can be performed between qubits 1276 and 1266, and between qubits 1288 and 1282, to transfer quantum states between physical qubits designated for quantum computation and physical qubits designated for quantum entanglement, respectively.

[0090] The three examples above of logic multi-qubit gate operations using one physical qubit each of QPU1264, 1278, and 1290 can be understood as multi-qubit gate operations that can be executed in parallel or sequentially within the overall orchestration of the execution of a given quantum circuit, depending on the gate dependency of the quantum circuit, as further described above with respect to quantum circuit 1000.

[0091] As further described above with respect to at least quantum repeater 708, quantum repeater 1204 can be configured to provide a set of multiple logically designated quantum memories to provide a buffer of pairwise entanglement instances established between QPUs 1264, 1278, and 1290, as shown between quantum memory locations 1206 and 1224, 1208 and 1228, 1210 and 1230, 1212 and 1232, 1214 and 1238, and 1216 and 1240 in Figure 12. The optical switchboard 1202 may, according to some embodiments, be configured to route between any two quantum memory locations shown on quantum repeater 1204 to perform Bell state measurements as part of the process for providing distributed quantum computing, and similarly for the respective optical switchboards 1242, 1244, and 1246. Furthermore, the quantum repeater 1204 can be configured to remotely connect to a set of quantum memories locally connected to the QPUs 1264, 1278, and 1290 using optical communication links 1218, 1220, and 1222.

[0092] As further described above with respect to the modular quantum computing system 900, various optical transducers and / or optical interfaces 1248, 1250, and 1252 may be configured to enable the conversion of quantum information between a given qubit technology grouping type physical qubit (e.g., superconducting qubit) used to implement the QPUs 1264, 1278, and 1290, as shown in Figure 12, and a corresponding set of quantum memory used to establish and maintain pairwise entangled instances.

[0093] Figure 13 shows further examples of elastic quantum computing services, in several embodiments, that can be allocated various combinations of QPUs located in several different quantum hardware facilities for use when executing each quantum circuit.

[0094] In some embodiments, modular quantum computing systems, such as those described herein with reference to Figures 9, 11, and 12, may include QPUs (Quantum Processing Units) that span several different facilities within the Elastic Quantum Computing Service Provider Network 1300. For example, QPUs 1304 and 1312 may be located together in a facility on the service provider network 1302a. Although QPUs 1304 and 1312 may be located together in the same facility, the QPUs are physically separated from each other by at least one optical communication link. For example, as shown in Figure 13, QPUs 1304 and 1312 may be configured to provide distributed quantum computing via optical communication links 1324 and 1326 and via routing through a quantum repeater 1330. In some embodiments, the quantum repeater 1330 may be located in the same or different facilities on the service provider network. For example, the facilities of service provider networks 1302a and 1302b may be analogous to physically isolated components QPUs 1304 and 1312 and quantum repeater 1330 located in a given data center of elastic quantum computing service provider network 1300. In another example, QPUs 1304 and 1312 may be located in a first data center of elastic quantum computing service provider network 1300 and configured to provide distributed quantum computing with quantum repeater 1330 located in a second data center of elastic quantum computing service provider network 1300 via optical communication links 1324 and 1326.

[0095] Furthermore, as described above, various optical transducers 1306 and 1314, optical switchboards 1308 and 1316, and quantum memory sets 1310 and 1318 may be configured according to various qubit technology groupings of QPUs 1304 and 1312 to support orchestration that provides distributed quantum computing.

[0096] In some embodiments, the classical computing resource 1332 may be configured to allocate various QPUs made available via the elastic quantum computing service provider network 1300 for use in executing a given quantum circuit, and then determine and distribute gate scheduling instructions for executing the given quantum circuit. In some embodiments, as further described herein with reference to Figure 15, the classical computing resource 1332 may be analogous to one or more classical computing devices 1500 and / or have similar functionality to classical computing devices 1500.

[0097] In some embodiments, the elastic quantum computing service provider network 1300 may be configured to provide distributed quantum computing across one or more QPUs located outside the service provider network, such as any QPU located at the quantum hardware provider facility 1320. In such embodiments, a quantum repeater 1322 can be used to interface with one of each of the physical qubits of a given QPU located at the quantum hardware provider facility 1320, and to teleport quantum information related to distributed quantum computing between the QPU located at the quantum hardware provider facility 1320 and the service provider network 1302. Furthermore, a large geographical distance may exist between the quantum hardware provider facility 1320 and the facilities of the service provider network 1302, as represented by the optical communication link 1328. In such embodiments, a modular quantum computing system, such as the one shown in Figure 13, may be configured to provide verifiable blind quantum computing services and additional quantum secure computing services to customers of the elastic quantum computing service provider network 1300.

[0098] Figure 14 is a flowchart illustrating the process of executing quantum circuits using modular quantum computing resources of an elastic quantum computing service, according to several embodiments.

[0099] In block 1400, a request is received to execute a quantum circuit using two or more QPUs made accessible by the Elastic Quantum Computing Service, and the two or more QPUs are remotely connected using a quantum entanglement network. Furthermore, as described above, in order to provide on-demand distributed quantum computing services to customers of the Elastic Quantum Computing Service, a buffer of established pairwise quantum entanglement instances can be prepared and maintained without having to endure the latency that would normally be required if pre-prepared quantum entanglement were not actively pre-established for such distributed quantum computing.

[0100] In block 1402, the elastic quantum computing service determines the minimum number of physical qubits expected to be required to execute the quantum circuit, and thus can allocate a given number (e.g., at least two or more) of QPUs to be used to execute the quantum circuit.

[0101] In block 1404, gate scheduling instructions can be determined using classical computing resources of the elastic quantum computing service, such as classical computing resource 1332, so that the service can orchestrate the execution of quantum circuits across multiple allocated QPUs. As described above with respect to Figure 10B, the gate scheduling instructions include instructions for at least one multi-qubit quantum gate that is executed using physical qubits of two or more allocated QPUs.

[0102] In block 1406, during the execution of the quantum circuit, the quantum entanglement network utilized by the elastic quantum computing service is configured to teleport the quantum states associated with a given multi-qubit quantum gate between the physical qubits of the first QPU of the assigned QPU and the physical qubits of the second QPU of the assigned QPU. In block 1408, the execution results are provided following the completion of the remaining quantum gates of the given quantum circuit.

[0103] Embodiments of this disclosure may be described in consideration of the following provisions. Clause 1. A modular quantum computing system, A quantum entanglement network subsystem configured to remotely connect separate quantum processing units (QPUs) using optical communication links, The first QPU, A first set of physical qubits designated for quantum computation, A second set of physical qubits designated for quantum entanglement operations, The first QPU, including, It is the second QPU, A third set of physical qubits designated for quantum computing operations, A fourth set of physical qubits designated for quantum entanglement operations, A second QPU, including, To execute a given multi-qubit gate of a given quantum circuit between each of the first set of physical qubits and each of the third set of physical qubits, the quantum entanglement network subsystem, A modular quantum computing system further configured to teleport one quantum state from each of a second set of physical qubits to one from each of a fourth set of physical qubits. Clause 2. The quantum entanglement network subsystem is A first quantum repeater locally connected to a first QPU, the first quantum repeater includes a first set of quantum memory, A second quantum repeater locally connected to a second QPU, the second quantum repeater includes a second set of quantum memory, The quantum entanglement network subsystem is The modular quantum computing system described in Clause 1, further configured to establish one or more pairwise entangled instances with one quantum memory from each of the first set of quantum memories of the first quantum repeater and with each of the other quantum memories from the second set of quantum memories of the second quantum repeater, using one or more optical communication links. Clause 3. The first quantum repeater further comprises a first optical switchboard, To teleport one quantum state from each of the second set of physical qubits to one of each of the fourth set of physical qubits, the first optical switchboard is configured to perform a Bell state measurement between each of each of the second set of physical qubits and a given quantum memory from the first set of quantum memories. The second quantum repeater further includes a second optical switchboard, A modular quantum computing system according to Clause 2 or 3, wherein a second optical switchboard is configured to perform Bell state measurements between each of a fourth set of physical qubits and another given quantum memory from a second set of quantum memories, in order to teleport quantum states. Clause 4. The modular quantum computing system as described in Clause 3, further comprising an optical transducer configured to enable a first optical switchboard to interface with signals obtained from a second set of physical qubits in the first QPU. Clause 5. In order to execute a given multi-qubit gate of a given quantum circuit between each of the first set of physical qubits and each of the third set of physical qubits, the first QPU, A modular quantum computing system as described in any one of Clauses 1 to 4, further configured to perform one or more SWAP gate operations between each of a first set of physical qubits, one or more other physical qubits of the first set of physical qubits, and each of a second set of physical qubits. Clause 6. A modular quantum computing system as described in any one of Clauses 1 to 5, wherein the first QPU is further configured to execute one or more additional gates of a quantum circuit between each other physical qubit of the first set of physical qubits. Clause 7. A system, One or more classical computing devices in a service provider network configured to implement an elastic quantum computing service configured to orchestrate the execution of quantum circuits using multiple quantum processing units (QPUs) accessible via the service provider network, wherein one or more classical computing devices are configured to implement the elastic quantum computing service Allocating the number of QPUs from among multiple QPUs to be used when executing a given quantum circuit, Determining gate scheduling instructions to be applied during the execution of a given quantum circuit across an allocated number of QPUs, wherein one or more classical computing devices are further configured to schedule multi-qubit gates to be executed using the physical qubits of the first QPU and the physical qubits of the second QPU of the allocated number of QPUs, and further configured to do the following: It comprises a quantum entanglement network including multiple quantum repeaters locally connected to one of multiple QPUs, In order to perform a multi-qubit gate using the physical qubits of the first QPU and the physical qubits of the second QPU, the quantum entanglement network is configured to generate quantum entanglement between a first quantum repeater among a plurality of quantum repeaters locally connected to the first QPU and a second quantum repeater among a plurality of quantum repeaters locally connected to the second QPU. Clause 8. One or more classical computing devices implementing the Elastic Quantum Computing Service shall allocate several QPUs to be used when executing a given quantum circuit. Based at least partially on a given compiled version of the quantum circuit, the minimum number of physical qubits used to execute a given quantum circuit, Determine one or more combinations of QPUs from among multiple QPUs that yield at least the minimum number of physical qubits, The system described in Clause 7 is further configured to assign a number of QPUs to be used when executing a given quantum circuit, at least partially based on a combination of one or more QPUs. Clause 9. In order to determine one or more combinations of QPUs from among multiple QPUs that yield at least a minimum number of physical qubits, one or more classical computing devices implementing the elastic quantum computing service shall Determining which of the multiple QPUs are currently allocated or scheduled to be allocated for use when executing other quantum circuits, The system described in Clause 8, further configured to determine one or more combinations of QPUs that yield at least a minimum number of physical qubits, based at least in part on the determination of QPUs among a plurality of QPUs that are currently allocated or scheduled to be allocated for use in executing other quantum circuits. Clause 10. One or more classical computing devices that implement elastic quantum computing services, The system according to any one of the clauses 7 to 9, which generates entangled instructions to be provided to a quantum entanglement network before executing a given quantum circuit across an allocated number of QPUs, the entangled instructions being further configured to indicate one or more pairwise entangled instances established between each of a plurality of quantum repeaters, at least in part on a determined gate scheduling instruction. Clause 11. The quantum entanglement network is configured to establish one or more pairwise quantum entanglement instances between each of a plurality of quantum repeaters, based at least in part on a provided quantum entanglement instruction, as described in Clause 10. Clause 12. The quantum entanglement network is further configured to maintain a buffer of established pairwise entanglement instances such that the rate at which one or more pairwise entanglement instances are established is higher than the decay rate of one or more pairwise entanglement instances. The decay rate of one or more pairwise entangled instances is based at least in part on the coherence time of the qubits in each of the multiple quantum repeaters, as described in Clause 11. Clause 13. In order to determine the gate scheduling instructions for a given quantum circuit across an allocated number of QPUs, one or more classical computing devices are further configured to schedule subsequent multi-qubit gates to be executed using additional physical qubits of the first QPU and the physical qubits of the third QPU of the allocated number of QPUs. The system described in any one of clauses 7 to 12, wherein subsequent multi-qubit gates depend at least partially on the output of a multi-qubit gate executed using the physical qubits of the first QPU and the physical qubits of the second QPU. Clause 14. The system further includes a third quantum repeater configured to establish one or more pairwise entangled instances with a first repeater and one or more additional pairwise entangled instances with a second repeater. The system according to any one of clauses 7 to 13, wherein the quantum entanglement network is configured such that distributed quantum entanglement is generated between the first quantum repeater and the third quantum repeater, and between the third second quantum repeater and the second quantum repeater, in order to perform a multiqubit gate using the physical qubits of the first QPU and the physical qubits of the second QPU. Article 15. The first QPU is located in a facility within the service provider network. The first quantum repeater is, A set of quantum memory, Including an optical switchboard, The system according to any one of Clauses 7 to 14, wherein the optical switchboard is configured to perform a Bell state measurement between a given quantum memory of a set of quantum memories designated for quantum entanglement operations and another physical qubit of the first QPU in order to perform a multi-qubit gate using the physical qubits of the first QPU and the physical qubits of the second QPU. Clause 16. The second QPU shall be located in a facility within the service provider network. The second quantum repeater is, Another set of quantum memory, Includes another optical switchboard, To perform a multi-qubit gate using the physical qubits of the first QPU and the physical qubits of the second QPU, another optical switchboard is configured to perform another Bell state measurement between another given quantum memory of another set of quantum memories designated for quantum entanglement operations and another physical qubit of the second QPU, the other given quantum memory of another set of quantum memories in the second QPU corresponds to an established pairwise entanglement instance with a given quantum memory of the set of quantum memories in the first QPU, as described in Clause 15. Article 17. Method, Receiving requests from customers of the Elastic Quantum Computing Service to execute quantum circuits using the quantum computing resources of the Elastic Quantum Computing Service, The arrangement involves allocating some of the multiple quantum processing units (QPUs) made available by the Elastic Quantum Computing Service for use in executing quantum circuits, wherein the allocated QPUs are remotely connected using quantum repeaters of a quantum entanglement network. This involves executing a quantum circuit using an allocated QPU, and executing a quantum circuit is This includes executing a given multi-qubit gate of a quantum circuit between a physical qubit of a first QPU among the allocated QPUs and a physical qubit of a second QPU among the allocated QPUs, wherein executing the given multi-qubit gate includes teleporting the quantum state associated with the given multi-qubit gate between another physical qubit of the first QPU designated for quantum entanglement and another physical qubit of the second QPU designated for quantum entanglement, Providing customers with the results of quantum circuit execution, Methods that include... Clause 18. Executing a given multi-qubit gate of a quantum circuit between the physical qubits of the first QPU and the physical qubits of the second QPU is: The method according to clause 17, further comprising performing one or more SWAP gate operations between a physical qubit of the first QPU and other physical qubits of the first QPU designated for quantum entanglement operations, before teleporting the quantum state. Clause 19. Executing a quantum circuit using an allocated QPU is permitted. In response to executing a given multi-qubit gate of a quantum circuit between the physical qubits of the first QPU and the physical qubits of the second QPU, The method according to Clause 17 or 18, further comprising using one or more of the allocated QPUs to execute one or more subsequent multi-qubit gates of a quantum circuit, wherein the one or more subsequent multi-qubit gates depend at least in part on the output of a multi-qubit gate executed between the physical qubits of the first QPU and the physical qubits of the second QPU. Clause 20. Allocating several QPUs for use when executing quantum circuits is permitted. Based at least partially on a given compiled version of the quantum circuit, the minimum number of physical qubits used to execute the quantum circuit, Determine one or more combinations of QPUs from among multiple QPUs that yield at least the minimum number of physical qubits, Allocating some QPUs based at least partially on one or more combinations of QPUs, The method described in any one of clauses 17 to 19, including the method described in any one of clauses 17 to 19. Clause 21. A system, The first quantum repeater of a service provider network, The first set of quantum memory, A second set of quantum memory, wherein the first quantum repeater is configured to maintain a buffer of established pairwise entanglement instances between the second set of quantum memory and the third set of quantum memory of the second quantum repeater, An optical switchboard configured to perform a Bell state measurement between one of the first set of quantum memories and one of the second set of quantum memories, An interface configured to display the results of Bell condition measurement, The first quantum repeater includes, A second quantum repeater in a service provider network, connected to a first quantum repeater by an optical communication link, wherein the second quantum repeater is The second quantum repeater includes a third set of quantum memory, and is configured to use the third set of quantum memory to maintain a buffer of established pairwise entangled instances. The second quantum repeater, A system that includes this. Clause 22. The first and second quantum repeaters are configured to maintain a buffer of established pairwise entangled instances such that the rate at which pairwise entangled instances are established is higher than the decay rate of pairwise entangled instances. The decay rate of pairwise entangled instances is based at least in part on the coherence time of the qubits in the second set of quantum memory and the third set of quantum memory, respectively, as described in Clause 21. Clause 23. The system according to Clause 21 or 22, wherein the first and second quantum repeaters are configured to apply wavelength division multiplexing to enable multiple coexisting pairwise entangled quantum instances across an optical communication link. Clause 24. The system according to any one of Clauses 21 to 23, wherein the optical switchboard is further configured to select a given quantum memory from a second set to be used in a given Bell state measurement, at least in part on the determination that a given established pairwise entangled instance corresponding to a given quantum memory from a second set was established more recently than another of the established pairwise entangled instances. Clause 25. The system according to any one of Clauses 21 to 23, wherein the optical switchboard is further configured to select a given quantum memory from a second set to be used in a given Bell state measurement, at least in part on the determination that a given established pairwise entangled instance corresponding to a given quantum memory from a second set was established earlier than another of the established pairwise entangled instances. Clause 26. The first quantum repeater further includes a fourth set of quantum memory, and the first quantum repeater is further configured to maintain an additional buffer of established pairwise entanglement instances between the fourth set of quantum memory and the fifth set of quantum memory of the third quantum repeater of the service provider network. The system according to any one of clauses 21 to 25, wherein the optical switchboard is further configured to perform Bell state measurements between any one of the first set of quantum memories and any one of the fourth set of quantum memories. Clause 27. The first quantum repeater is further configured to logically reallocate one or more of the second set of quantum memories to a fourth set of quantum memories such that the additional buffer for established pairwise entanglement instances between the first quantum repeater and the third quantum repeater increases. The redesignation is at least partially, The buffer utilization of the established pairwise entanglement instance between the first and second quantum repeaters, The system described in Clause 26, based on another utilization of additional buffers for established pairwise entanglement instances between the first quantum repeater and the third quantum repeater. Article 28. The first quantum repeater further comprises one or more classical computing devices, Receiving a messenger signal indicating that quantum information has been stored in a given quantum memory of the first set, The quantum memory storage information indicating a specific quantum memory location of a given set of quantum memories is provided to the optical switchboard for the execution of Bell state measurements, A system configured to perform any one of the provisions 21 to 27. Clause 29. One or more classical computing devices shall receive the results of Bell state measurements via an interface, The system described in Clause 28 is further configured to provide the results of Bell state measurements to one or more additional classical computing devices in the service provider network for use in providing distributed quantum entanglement. Clause 30. In response to the performance of a Bell state measurement, the first quantum repeater and the second quantum repeater, The system described in any one of the clauses 21 to 29, further configured to retry establishing another pairwise entangled instance using the available quantum memory of each of the second set and the available quantum memory of each of the third set, so that a buffer of established pairwise entangled instances is maintained. Clause 31. A system, A quantum entangled network of a service provider network containing multiple quantum repeaters, The quantum entanglement network is configured to maintain a buffer of established pairwise quantum entanglement instances between each quantum memory location of the quantum repeaters. Multiple quantum repeaters are quantum repeaters in a service provider network. Quantum entanglement networks and, One or more classical computing devices in a service provider network are configured to implement a distributed quantum entanglement service, which is configured to orchestrate distributed quantum entanglement across the endpoints of the service provider network using one of several quantum repeaters, wherein one or more classical computing devices are configured to implement the distributed quantum entanglement service, Receiving a request from a customer of a distributed quantum entanglement service to provide distributed quantum entanglement between the customer's endpoint and another endpoint in the service provider network, Determining an optical communication path between a customer endpoint and another endpoint of the service provider network, wherein the optical communication path includes an intersection point at one or more of a plurality of quantum repeaters. Dispersive quantum entanglement is provided between the quantum memory locations of one or more quantum repeaters, using one of each of the already established pairwise entanglement instances maintained in a buffer, One or more classical computing devices, further configured to perform the following: A system equipped with these features. Clause 32. A given one of a plurality of quantum repeaters includes an optical switchboard configured to perform a Bell state measurement between any two quantum memory locations in the given one of the plurality of quantum repeaters. Dispersive quantum entanglement is provided between the quantum memory locations of one or more quantum repeaters, using one of each of the already established pairwise entanglement instances maintained in a buffer. The system according to Clause 31, wherein one of a given number of quantum repeaters is configured to provide the result of a Bell state measurement corresponding to one of the already established pairwise entangled instances in a buffer. Clause 33. The quantum entanglement network is configured to maintain a buffer of established pairwise entanglement instances between each quantum memory location of the quantum repeater such that the rate at which pairwise entanglement instances are established is higher than the decay rate of pairwise entanglement instances. The decay rate of pairwise entangled instances is based at least in part on the coherence time of the qubits in each of the quantum memory locations of the quantum repeater, as described in Clause 31 or Clause 32. Clause 34. The quantum entanglement network is configured to maintain a buffer of established pairwise entanglement instances between each quantum memory location of the quantum repeater such that the rate at which pairwise entanglement instances are established is faster than the rate at which pairwise entanglement instances are consumed. The consumption rate of pairwise entangled instances is at least in part based on providing distributed entanglement using one of each of the already established pairwise entangled instances maintained in a buffer, as described in any one of the systems described in any one of the clauses 31 to 33. Clause 35. To orchestrate distributed quantum entanglement, one or more classical computing devices that implement distributed quantum entanglement services may be used. Evaluating the elapsed time since the establishment of each established pairwise entanglement instance in the buffer, In response to the detection that one of the evaluated elapsed times is greater than the coherence time of the qubit in each quantum memory location corresponding to one of the already established pairwise entanglement instances, To maintain the buffer, the establishment of another pairwise entangled instance corresponding to each quantum memory location is retried, A system as described in any one of clauses 31 to 34, further configured to perform the following actions. Article 36. To orchestrate distributed quantum entanglement, one or more classical computing devices that implement distributed quantum entanglement services may be used. In response to providing distributed quantum entanglement using each of the already established pairwise entanglement instances maintained in the buffer, To maintain the buffer, the establishment of one or more additional pairwise quantum entanglement instances is retried, The system described in clauses 31-35, further configured to perform the following actions. Article 37. To orchestrate distributed quantum entanglement, one or more classical computing devices that implement distributed quantum entanglement services may be used. Monitoring the consumption rate of established pairwise entangled instances in the buffer between each of the quantum repeaters, Based at least partially on changes in the monitored consumption rate, one or more quantum memory locations within a given quantum repeater among multiple quantum repeaters are logically re-specified for use in establishing other pairwise quantum entanglement instances with different quantum repeaters among multiple quantum repeaters, A system as described in any one of clauses 31 to 36, further configured to perform the following: Article 38. Method, Maintaining a buffer of established pairwise entanglement instances between the quantum memory location of a first quantum repeater and the quantum memory location of a second quantum repeater, wherein the first and second quantum repeaters are quantum repeaters of a service provider network, In response to receiving a request from a customer of the service provider network to provide distributed quantum entanglement between the customer's endpoint and another endpoint of the service provider network, Using the optical switchboard in the first quantum repeater, One of the quantum memory locations of the first quantum repeater corresponds to one of the established pairwise entanglement instances in the buffer, Another quantum memory location in the first quantum repeater, corresponding to the location that stores quantum information about entangled photons received by the first quantum repeater, and Perform bell condition measurements during the interval, Using the optical switchboard in the second quantum repeater, One of the quantum memory locations of the second quantum repeater corresponds to one of the established pairwise entanglement instances in the buffer, Another quantum memory location in the second quantum repeater, corresponding to a location that stores quantum information about another entangled photon received by the second quantum repeater, and Performing another Bell State measurement in between, To provide the results of a Bell state measurement performed in a first quantum repeater and the results of another Bell state measurement performed in a second quantum repeater, Methods that include... Clause 39. In response to the execution of a Bell state measurement and other Bell state measurements corresponding to one of the established pairwise entangled instances in the buffer, The method according to clause 38, further comprising re-establishing another pairwise entanglement instance between the first quantum repeater and the second quantum repeater so that the buffer is maintained. Clause 40. Evaluate the time elapsed since the establishment of each established pairwise entanglement instance in the buffer, In response to detecting that one of the evaluated elapsed times is greater than the coherence time of the qubits in the respective quantum memory locations of the first and second quantum repeaters, To maintain the buffer, another pairwise quantum entanglement instance is re-established, The method described in Clause 38 or Clause 39, further including the method described in Clause 38 or Clause 39.

[0104] Exemplary computer system Figure 15 is a block diagram showing an exemplary computing device that may be used in at least some embodiments.

[0105] Figure 15 shows a general-purpose classical computing device 1500 that may be used in any of the embodiments described herein. In the illustrated embodiment, the classical computing device 1500 includes one or more processors 1510 coupled to system memory 1520 (which may include both non-volatile and volatile memory modules) via an input / output (I / O) interface 1530. The classical computing device 1500 further includes a network interface 1540 coupled to the I / O interface 1530.

[0106] In various embodiments, the classic computing device 1500 may be a uniprocessor system including one processor 1510, or a multiprocessor system including several processors 1510 (e.g., two, four, eight, or another suitable number). The processors 1510 may be any suitable processor capable of executing instructions. For example, in various embodiments, the processors 1510 may be general-purpose or embedded processors implementing one of various instruction set architectures (ISAs), such as x86, PowerPC, SPARC, or MIPS ISA, or any other suitable ISA. In a multiprocessor system, each of the processors 1510 may, but not necessarily, implement the same ISA in general. In some implementations, a graphics processing unit (GPU) may be used instead of, or in addition to, the conventional processors.

[0107] The system memory 1520 may be configured to store instructions and data accessible by the processor 1510. In at least some embodiments, the system memory 1520 may have both volatile and non-volatile portions, while in other embodiments, only volatile memory may be used. In various embodiments, the volatile portion of the system memory 1520 may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM, or any other type of memory. In the case of the non-volatile portion of the system memory (which may include, for example, one or more NVDIMMs), in some embodiments, a flash-based memory device including a NAND flash device may be used. In at least some embodiments, the non-volatile portion of the system memory may include a power source such as a supercapacitor or other power storage device (e.g., a battery). In various embodiments, any of memristor-based resistive random access memory (ReRAM), 3D NAND technology, ferroelectric RAM, magnetoresistive RAM (MRAM), or various types of phase-change memory (PCM) may be used for at least the non-volatile portion of the system memory. In the illustrated embodiment, program instructions and data that implement one or more desired functions, such as the methods, techniques, and data described above, are stored and shown in system memory 1520 as code 1525 and data 1526.

[0108] In some embodiments, the I / O interface 1530 may be configured to coordinate I / O traffic between the processor 1510, system memory 1520, and any peripheral devices in the device, including network interface 1540 or other peripheral interfaces such as various types of persistent and / or volatile storage devices. In some embodiments, the I / O interface 1530 may perform any necessary protocols, timing, or other data conversions to convert data signals from one component (e.g., system memory 1520) into a format suitable for use by another component (e.g., processor 1510). In some embodiments, the I / O interface 1530 may include support for devices connected via various types of peripheral buses, such as a PCI bus standard or a variation of the Universal Serial Bus (USB) standard. In some embodiments, the functionality of the I / O interface 1530 may be divided into two or more separate components, such as a northbridge and a southbridge. Also, in some embodiments, some or all of the functionality of the I / O interface 1530, such as the interface to system memory 1520, may be directly incorporated into the processor 1510.

[0109] The network interface 1540 may be configured to exchange data between the classic computing device 1500 and other devices 1560 connected to one or more networks 1550, such as other computer systems or devices as shown in Figures 1 to 14. In various embodiments, the network interface 1540 can support communication over any suitable wired or wireless general data network, such as an Ethernet® network. Additionally, the network interface 1540 can support communication over telecommunications / telephone networks, such as analog voice networks or digital fiber optic networks, over storage area networks, such as Fibre Channel SANs, or over any other suitable type of network and / or protocol.

[0110] In some embodiments, system memory 1520 may represent an embodiment of a computer-accessible medium configured to store at least a subset of program instructions and data used to implement the methods and apparatus discussed in the context of Figures 1 to 14. However, in other embodiments, program instructions and / or data may be received, transmitted, or stored on different types of computer-accessible media. Generally speaking, the computer-accessible medium may include magnetic or optical media, such as disks or non-temporary storage media or memory media, coupled to the classical computing device 1500 via an I / O interface 1530. The non-temporary computer-accessible storage medium may also include any volatile or non-volatile media such as RAM (e.g., SDRAM, DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc., which may be included in some embodiments of the classical computing device 1500 as system memory 1520 or another type of memory. In some embodiments, multiple non-temporary computer-readable storage media may collectively store program instructions that, when executed on or across one or more processors, implement at least a subset of the methods and techniques described above. The computer-accessible medium may further include transmission media or signals, such as electrical, electromagnetic, or digital signals, transmitted over communication media such as networks and / or wireless links, which may be implemented via the network interface 1540. The functions described in various embodiments can be implemented using some or all of a set of classic computing devices, as shown in Figure 15; for example, software components running on various different devices and servers can cooperate to provide the functionality. In some embodiments, some of the described functionality may be implemented using a storage device, network device, or dedicated computer system, in addition to being implemented using a general-purpose computer system.As used herein, the term “classic computing device” refers to, but is not limited to, at least all of these types of devices.

[0111] conclusion Various embodiments may further include receiving, transmitting, or storing instructions and / or data implemented on a computer-accessible medium in accordance with the above description. Generally speaking, computer-accessible mediums may include storage or memory media such as magnetic or optical media, e.g., disks or DVD / CD-ROMs, RAM (e.g., SDRAM, DDR, RDRAM, SRAM, etc.), volatile or nonvolatile media such as ROM, and transmission media or signals such as electrical, electromagnetic, or digital signals transmitted over communication media such as networks and / or wireless links.

[0112] The various methods shown in the figures and described herein represent exemplary embodiments of the methods. The methods may be implemented in software, hardware, or a combination thereof. The order of the methods may be changed, and various elements may be added, rearranged, combined, omitted, modified, etc.

[0113] Various modifications and changes can be made, as will be apparent to those skilled in the art who are interested in this disclosure. The above description is intended to encompass all such modifications and changes, and therefore should be considered illustrative rather than restrictive.

Claims

1. It is a system, A quantum entangled network of a service provider network containing multiple quantum repeaters, The quantum entanglement network is configured to maintain a buffer of established pairwise quantum entanglement instances between each quantum memory location of the quantum repeater. The aforementioned plurality of quantum repeaters are quantum repeaters of a service provider network, a quantum entanglement network, One or more classical computing devices in the service provider network are configured to implement a distributed quantum entanglement service configured to orchestrate distributed quantum entanglement across the endpoints of the service provider network using one of the plurality of quantum repeaters, To implement the distributed quantum entanglement service, the one or more classical computing devices are equipped with, Receiving a request from a customer of the distributed quantum entanglement service to provide distributed quantum entanglement between the customer's endpoint and another endpoint of the service provider network, Determining an optical communication path between the customer's endpoint and the other endpoint of the service provider network, wherein the optical communication path includes an intersection point in one or more of the plurality of quantum repeaters. Providing the distributed quantum entanglement between the quantum memory locations of one or more quantum repeaters, using each of the already established pairwise entanglement instances maintained in the buffer, A system further configured to perform the following actions.

2. A given one of the plurality of quantum repeaters includes an optical switchboard configured to perform a Bell state measurement between any two quantum memory locations in the given one of the plurality of quantum repeaters. Dispersive quantum entanglement is provided between the quantum memory locations of the one or more quantum repeaters, using each of the already established pairwise entanglement instances maintained in the buffer. The system according to claim 1, wherein one of the plurality of quantum repeaters is configured to provide the result of the Bell state measurement corresponding to one of the already established pairwise entangled instances in the buffer.

3. The system according to claim 2, wherein the optical switchboard is further configured to select the given quantum memory of the given quantum repeater to be used in a given Bell state measurement, at least in part on the determination that a given established pairwise entanglement instance corresponding to the given quantum memory of the given quantum repeater was established more recently than another of the established pairwise entanglement instances.

4. One of the quantum repeaters, given, further includes one or more classical computing devices, Receiving a messenger signal indicating that quantum information has been stored in a given quantum memory of the first set, The quantum memory storage information indicating a specific quantum memory location of the given quantum memory of the first set is provided to the optical switchboard for the execution of the Bell state measurement, The system according to claim 2, configured to perform the following:

5. The quantum entanglement network is configured to maintain the buffer of established pairwise entanglement instances between each quantum memory location of the quantum repeater such that the rate at which pairwise entanglement instances are established is higher than the decay rate of the pairwise entanglement instances. The system according to any one of claims 1 to 4, wherein the decay rate of the pairwise entangled instances is at least partially based on the coherence time of the qubits in each of the quantum memory locations of the quantum repeater.

6. The quantum entanglement network is configured to maintain the buffer of established pairwise entanglement instances between each quantum memory location of the quantum repeater such that the rate at which pairwise entanglement instances are established is higher than the consumption rate of pairwise entanglement instances. The system according to any one of claims 1 to 4, wherein the consumption rate of the pairwise entanglement instances is at least in part based on using one of the already established pairwise entanglement instances maintained in the buffer to bring about the provision of the distributed entanglement.

7. To orchestrate distributed quantum entanglement, one or more classical computing devices that implement the distributed quantum entanglement service, Evaluating the elapsed time since establishment of each of the established pairwise entangled instances in the buffer, In response to the detection that one of the evaluated elapsed times is greater than the coherence time of the qubit in each of the quantum memory locations corresponding to one of the already established pairwise entanglement instances, To maintain the buffer, the establishment of another pairwise entangled instance corresponding to each of the quantum memory locations is retried, The system according to any one of claims 1 to 4, further configured to perform the following:

8. To orchestrate distributed quantum entanglement, one or more classical computing devices that implement the distributed quantum entanglement service, In response to providing the aforementioned distributed quantum entanglement, use one of the previously established pairwise quantum entanglement instances maintained in the buffer, To maintain the buffer, the establishment of one or more additional pairwise entanglement instances is retried, The system according to claim 1, further configured to perform the following:

9. To orchestrate distributed quantum entanglement, one or more classical computing devices that implement the distributed quantum entanglement service, Monitoring the consumption rate of the established pairwise entangled instances in the buffer between each of the quantum repeaters, Based at least in part on the changes in the monitored consumption rate, one or more of the quantum memory locations within a given quantum repeater among the plurality of quantum repeaters are logically re-designated for use in establishing other pairwise quantum entanglement instances with different quantum repeaters among the plurality of quantum repeaters, The system according to claim 1 or claim 8, further configured to perform the following:

10. The system according to claim 1, wherein one or more of the plurality of quantum repeaters are configured to apply wavelength division multiplexing to enable a plurality of coexisting pairwise entangled quantum instances across the optical communication path.

11. The system according to claim 1, wherein the distributed quantum entanglement service is further configured to select the given quantum memory from the second set to be used in a given Bell state measurement, at least in part on the determination that a given established pairwise entanglement instance corresponding to a given quantum memory from the second set was established more recently than another of the established pairwise entanglement instances.

12. It is a method, Receiving a request from a customer of a service provider network's distributed quantum entanglement service to provide distributed quantum entanglement between the customer's endpoint and another endpoint of the service provider network, Determining an optical communication path between the customer's endpoint and the other endpoint of the service provider network, wherein the optical communication path includes an intersection point at one or more of the service provider network's quantum repeaters. Using one of the already established pairwise entanglement instances maintained in the buffer, the distributed quantum entanglement is provided, Methods that include...

13. In response to the reception of the request from the customer of the service provider network, provide the distributed quantum entanglement between the customer's endpoint and another endpoint of the service provider network. Using the optical switchboard in the given quantum repeater, One of the quantum memory locations of the given quantum repeater, corresponding to one of the established pairwise entanglement instances in the buffer, A location in the given quantum repeater that stores quantum information about entangled photons received by the given quantum repeater, and Perform bell condition measurements during the interval, Using the optical switchboard in the second quantum repeater, One of the quantum memory locations of a second quantum repeater corresponding to one of the established pairwise entanglement instances in the buffer, Another quantum memory location in the second quantum repeater, corresponding to a location that stores quantum information about another entangled photon received by the second quantum repeater, and Performing another Bell State measurement in between, To provide the results of the Bell state measurement performed in the given quantum repeater and the results of the other Bell state measurement performed in the second quantum repeater, The method according to claim 12, further comprising:

14. In response to the execution of the Bell state measurement and the execution of the other Bell state measurement, corresponding to one of the established pairwise entanglement instances in the buffer, The method according to claim 13, further comprising re-establishing another pairwise entanglement instance between the given quantum repeater and a second quantum repeater so that the buffer is maintained.

15. Evaluating the elapsed time since establishment of each of the established pairwise entangled instances in the buffer, In response to detecting that one of the evaluated elapsed times is greater than the coherence time of the qubits in the respective quantum memory locations of the first and second quantum repeaters, To maintain the aforementioned buffer, another pairwise entanglement instance is re-established, The method according to claim 13 or claim 14, further comprising:

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