Systems and methods for quantum caching

Abstract

The invention relates to a system and method for quantum caching. An entangled quantum cache includes a quantum repository that receives a plurality of quantum states and is configured to store and sort the plurality of quantum states and provide a selected one of the stored and sorted plurality of quantum states to a quantum data output at a first desired time. A fidelity system is configured to determine a fidelity of at least some of the plurality of quantum states. A classic repository is coupled to the fidelity system and configured to store classic data including the determined fidelity information and an index associating a particular one of the classic data with a particular one of the plurality of quantum states, and supply at least some of the classic data to the classic data output at a second desired time. A processor is connected to the classical repository and determines a first time based on the index.

Description

[0001] This application is a divisional application of the PCT international application with an international filing date of May 3, 2021, national application number 202180038958.8, and invention name “System and method for quantum caching” entering the Chinese national phase.

[0002] The section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described in this application in any way.

[0003] Related application section

[0004] This application is a non-provisional application of U.S. Provisional Patent Application Serial No. 63 / 020,221, filed on May 5, 2020 and entitled “System and Method for Quantum Cache.” The entire contents of U.S. Provisional Patent Application Serial No. 63 / 020,221 are incorporated herein by reference. Background Art

[0005] Today's information systems are highly distributed, and this trend is expected to continue, especially as next-generation wireless systems enable people and machines to stay connected anywhere, anytime. Applications and services increasingly rely on distributed information and processing to function, but also increasingly strive to operate, see, and feel like local systems. These kinds of future systems could benefit from improved methods of tagging, storing, and moving information, including systems that exploit so-called non-local operations and resources. For example, methods and systems that can provide precise location and timing information that are not dependent on communication channels or sensitive to time-of-flight delays of those channels are highly desirable.

[0006] Furthermore, because large amounts of information, including highly personal, confidential, and sensitive information, are integral to applications and services that people and machines rely on, improved methods for securely marking, storing, and moving this information are also highly desirable. For example, methods for addressing that do not rely on sending plain text addresses over communications links are desirable. In many cases, traditional classical systems have reached their technological limits in providing features that address these critical issues. Quantum solutions could provide many important improvements. However, there are currently no practical quantum systems that can be seamlessly and efficiently adapted to classical information systems, allowing the underlying quantum phenomena to be used to improve performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] According to preferred and exemplary embodiments, the present teachings together with their further advantages are described in more detail in the following detailed description in conjunction with the accompanying drawings. It will be understood by those skilled in the art that the drawings described below are for illustration purposes only. The drawings are not necessarily drawn to scale, but generally emphasize the principles of the teachings. The drawings are not intended to limit the scope of the applicant's teachings in any way.

[0008] Figure 1 A distributed system of caches that can exploit quantum entanglement in accordance with the present teachings is illustrated.

[0009] Figure 2 The combination according to the present teaching is shown Figure 1 An embodiment of a portion of a distributed system is described, the system comprising a node using a cache of quantum entanglement and a node using an entanglement server.

[0010] Figure 3 A block diagram of an embodiment of a cache of quantum entanglement in accordance with the present teachings is illustrated.

[0011] Figure 4 An embodiment of a table showing a cache structure of a quantum entangled cache according to the present teachings is illustrated.

[0012] Figure 5A A diagram illustrating an embodiment of a multi-layer quantum storage repository according to the present teachings is illustrated.

[0013] Figure 5B A table showing a cache structure of a multi-layer quantum entangled cache according to the present teachings is illustrated.

[0014] Fig. 6A An embodiment of a bus network using an entangled cache in accordance with the present teachings is illustrated.

[0015] Figure 6B A table illustrating an embodiment of the structure of an entangled qubit cache for a multi-node network according to the present teachings is illustrated.

[0016] Figure 7 Illustrated is a block diagram of an embodiment of a quantum-enabled information system using an entangled quantum cache in accordance with the present teachings.

[0017] Figure 8 A block diagram of an embodiment of a control system for controlling an entangled quantum cache interacting with an application according to the present teachings is illustrated.

[0018] Fig. 9 An embodiment of a distributed system for providing metadata using an entangled cache in accordance with the present teachings is illustrated.

[0019] Fig.10 The diagram illustrates the application of a known quantum ultra-dense encoding and decoding scheme operating between a sender and a receiver.

[0020] Fig.11 An embodiment of an ultra-dense codec system using an entangled cache in accordance with the present teachings is illustrated.

[0021] Fig.12 Another embodiment of an ultra-dense codec system using an entangled cache in accordance with the present teachings is illustrated. DETAILED DESCRIPTION

[0022] The present teaching will now be described in more detail with reference to the exemplary embodiments shown in the accompanying drawings. Although the present teaching is described in conjunction with various embodiments and examples, the present teaching is not intended to be limited to such embodiments. On the contrary, as will be appreciated by those skilled in the art, the present teaching encompasses various substitutions, modifications and equivalents. Those of ordinary skill in the art who obtain the teachings herein will recognize additional embodiments, modifications and embodiments and other fields of use within the scope of the present disclosure as described herein.

[0023] References in the specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the teachings. The phrase "in one embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment.

[0024] It should be understood that the various steps of the method of this teaching can be performed in any order and / or simultaneously, as long as the teaching remains operable. In addition, it should be understood that the apparatus and method of this teaching can include any number or all of the described embodiments, as long as the teaching remains operable.

[0025] The present teachings relate to integrating quantum systems into conventional classical information systems to form various quantum information systems. These quantum information systems rely on their fundamental properties of quantization, superposition, entanglement, and / or nonlocality to provide various performance advantages and new features over similar classical versions of information system technologies. Some known examples of quantum information systems include quantum key distribution systems, analog and digital quantum computers, quantum communication links, and quantum sensors.

[0026] A particularly useful quantum object is a quantum qubit, which is a superposition of two fundamental states, generally described by Dirac notation as |0> and |1>. Different physical manifestations of qubits, such as superconducting qubits, optical qubits, and atomic qubits, have different physical manifestations for these fundamental states. However, these different manifestations can be expressed using similar mathematical representations, and they behave similarly in quantum systems. It should be understood that the present teachings can be applied to multiple manifestations of quantum qubit systems.

[0027] A qubit coherent superposition of basis states can be represented as |ψ〉=α|0〉+β|1〉, where α and β are complex numbers representing the probability amplitude of each basis state governed by the Schrödinger equation, which describes how a state evolves over time based on its energy environment. The probability distribution, which is the magnitude of the square of the probability amplitude, indicates the probability that |0〉 or |1〉 will result from a measurement of the qubit.

[0028] It is now widely accepted in the art that qubits can be entangled, which allows future measurements of specific ones of their physical properties to be perfectly correlated with the other qubits with which they are entangled. This feature of qubit entanglement holds true even if the entangled qubits are separated in time and / or space. This is due, at least in part, to the quantized nature of the entangled quantum system, and the fact that the wave function describing the quantum probabilities of various superpositions of states of the system collapses to a single quantized state upon measurement.

[0029] Another feature of qubit entanglement is that, as defined by quantum theory, measurement affects the entire entangled system, leading to a phenomenon in which a measurement at one location results in a result in the form of a collapsed state at another location that is perfectly correlated to the measured state (commonly referred to as wave function collapse). This wave function collapse, and the result of the associated perfect correlation at the two locations, makes entangled qubits and, more generally, entangled distributed quantum systems particularly useful resources in numerous types of information systems.

[0030] It should be understood that observing a quantum state is not necessarily a measurement of the quantum state. Measurement is an action that collapses the state of the wave function that describes the entangled system. Physicists often define measurement as the action of probing a path or deterministically distinguishing one of the possible states of an entangled system. Once observed through measurement, the state of the quantum system is no longer in a superposition state and can no longer maintain long-term correlations across its distributed system. More precisely, the system irreversibly abandons this type of connection.

[0031] Various aspects of the present teachings take advantage of the fact that quantum systems provide the ability to establish the fidelity of entanglement separately from measurement. In general, the fidelity of entanglement is a measure used to compare quantum states. The concept of fidelity of entanglement is straightforward in the case of pure states, but is more subtle for mixed quantum states found in real systems. In other words, quantum measurements are separate from other observations of the quantum state that allow one to determine whether the state is still entangled. In fact, there are many methods that can be used to probe the entanglement of a quantum state without disturbing the entanglement, so that a collapse of the quantum state occurs and the system is no longer entangled.

[0032] Many quantum systems according to the present teachings take advantage of the fact that quantum aspects of the system can be prepared to have entangled states and physically or virtually distributed across various physical locations. These entangled states can be measured to provide perfectly correlated states to be determined at remote locations. One feature of these systems is that no physical channel is required to provide such correlated state determination. In various embodiments, the quantum entangled systems of the present teachings are separated in space and / or time. Therefore, various aspects of the present teachings advantageously take advantage of the fact that the state collapse that provides correlated state determination at two locations occurs instantaneously and does not take into account any aspect of the distance between those locations and / or the precise locations of those locations.

[0033] In addition, various aspects of the present teachings advantageously exploit the fact that any external influence (such as an eavesdropper) that makes a measurement of a quantum system will destroy the associated entanglement, thereby causing a state collapse. This state collapse can be determined by various known mechanisms and protocols. Any observed or otherwise tampered qubit or quantum subsystem that depends on the quantum state can be discarded or ignored because it no longer contains useful information. Therefore, another aspect of the present teachings is that information systems according to the present teachings can operate securely and / or ensure privacy from eavesdroppers or various external influences on any results or measurements.

[0034] Another feature of the present teachings is the recognition that hybrid quantum / classical systems can still continue to operate over various classical channels, and / or use classical connections to manage the information they process, store, and transmit. As such, various embodiments of the systems and methods of the present teachings still maintain data in a classical state, and rely on any results or measurements associated with the various entangled qubits as classical metadata, rather than the quantum state itself.

[0035] Another feature of the present teachings is the recognition that management mechanisms are needed or at least highly desired to control and manage the distribution and storage of quantum states. Depending on the specific application and the method of generating quantum states, any of a variety of mechanisms can be used to transmit and store quantum states. The mechanisms used to control and manage quantum physical systems that generate quantum states must recognize the key performance attributes of physical qubits, combined with the needs of systems that are using quantum states for various applications. In other words, a feature of the present teachings is to provide various methods and devices for providing (one or more) appropriate abstractions operating between quantum physical systems that supply quantum states and classical, semi-classical and / or quantum information systems that use quantum states for various applications. (One or more) abstractions make it possible for system designers who are unfamiliar with the field of quantum systems but familiar with the field of classical systems to include quantum systems as part of the design solution, thereby providing a relatively simple interface bridge between quantum systems and classical systems.

[0036] Many important quantum applications utilize entangled qubits distributed in a network.The term "network" as used herein is a very broad term that refers to a collection of two or more nodes with associated information. Figure 1 An embodiment of a distributed system 100 for caching quantum entanglement according to the present teaching is illustrated. A plurality of nodes 102 are connected by a link 104. In general, the node 102 includes both a quantum system and a classical system. Moreover, in general, the link may include a classical transport or connection, may also include a quantum transport or connection, and may also include a link that can transport and / or connect both quantum and classical data, as described herein. The distributed system 100 is a mesh topology with nodes 102, 102' and links 104. However, it should be understood that the present teaching can be applied to a variety of different hybrid topologies. For example, the present teaching can be applied to bus, star, tree, ring, point-to-point, hybrid and other network topologies.

[0037] In some embodiments of the distributed system 100, entangled pairs, or more generally, larger groupings of N entangled qubits (such as three, four, or more entangled qubits in a group) need to be available when needed in any number of entangled dimensions K. In other words, the distributed quantum entanglement cache of the present teachings can include a source of entangled quantum states that generates a quantum state having multiple entangled quantum states. Thus, a qubit can be shared with N nodes and include K basis states. When used in nodes 102, 102', the qubit is entangled and coherent to some extent. Therefore, for some configurations, a mechanism is used in nodes 102, 102' to ensure coherent qubits and discard incoherent qubits.

[0038] In some embodiments of a system according to the present teachings, a mechanism is used at a node 102, 102' or elsewhere to supply verified coherent qubits. Also, in some embodiments of a system according to the present teachings, a mechanism is used to ensure that more than a predetermined percentage of coherent qubits are supplied from the pool of qubits available in a node.

[0039] In addition, it is important to index the qubits so that pairing is maintained between the qubits in one node 102 compared to another node 102'. Some embodiments of a quantum distributed system 102 according to the present teachings have mechanisms to ensure access to qubits with a latency compatible with a particular application. For example, a mechanism can be used to appropriately synchronize the availability of a set of 2-N entangled qubits between 2-N nodes 102, 102' to ensure the desired access latency and support pairing of those qubits. Indexing in nodes 102, 102' allows various paired or N-way entangled quantum states to be identified with each other. That is, an index can be used to indicate which other node's quantum state(s) a particular quantum state is entangled with.

[0040] and Figure 1 Embodiments of the distributed system 100 in the associated description and other embodiments described herein describe the use of a cache that includes entangled quantum states. However, it should be understood that the caches of the present teachings are not limited to entangled quantum states. As described herein, embodiments of quantum storage repositories and quantum caches can include and utilize quantum states that are not entangled states and / or are entangled quantum states.

[0041] Figure 2 The diagram shows a Figure 1 An embodiment of a portion of a distributed system 200 of the invention, wherein a node 202 performs as an entanglement server using an entanglement generator 204, and nodes 206, 206' use a cache 208, 208' of quantum entanglement. The nodes 202 are connected by links 210, 210'. Many embodiments of the present teachings use centralized and / or distributed mechanisms to distribute entangled qubits.

[0042] The entangled qubits are provided by the entanglement generator 204. For clarity, Figure 2 The distributed system 200 shown in only illustrates two nodes 206, 206' receiving entangled qubits, and a node 202 connected to two links 210, 210', which provides entangled quantum resources on those links 210, 210'. The distributed system 200 according to the present teaching is not limited to this. For example, many nodes can receive entangled resources. The entangled resource generator 204 can generate entanglement across more than two qubits, and therefore can provide entanglement across more than two links 210, 210'. The nodes 202, 206, 206' can include one or both of the server node resources 204 and the cache resources 208, 208'. Moreover, multiple entangled qubit generators 204 can be connected to different and / or the same caches 208, 208'. It should be understood that various quantum and classical network connections can be implemented using the present teachings.

[0043] A feature of the present teachings is the recognition that deterministic and on-demand sources of entangled photons can be easily integrated into a system using classical indexing corresponding to a particular quantum state and other information associated with the generation of the quantum state. An ideal deterministic source produces entangled photons at a known time and with 100% fidelity. In practice, deterministic sources approach those goals with a known and / or characterizable high probability (and / or fidelity) of producing a pair of entangled photons or a set of entangled photons at a known time. Although these terms are often used interchangeably, for the purposes of this article, an on-demand source produces entangled photons at an arbitrary but controllable time, while a deterministic source produces entangled photons at a known predetermined time with a high probability. Importantly, both types of controllable emission quantum entangled photon sources can be attached with associated classical data, including indexing information and quantum integrity information. The associated classical data can be referred to as metadata.

[0044] Some embodiments of the entanglement server 204 use a deterministic source of entangled photons generated by multiplexing and / or switching of non-deterministic quantum photon sources. Many known high-brightness sources of entangled photons are so-called non-deterministic sources, which produce entangled photon pairs (and larger entangled sets), but at random times. For example, spontaneous parametric down-conversion (SPDC), four-wave mixing, and various other nonlinear parametric processes are known to provide entangled photons at high rates, but with uncertain emission times. Multiple systems and methods have been shown to provide deterministic photon sources using multiplexing and / or switching schemes combined with non-deterministic sources. See, for example, Evan Meyer-Scott, Christine Silberhorn, and Alan Migdall, "Single-photon sources: Approaching the Ideal through multiplexing", Review of Scientific Instruments 91, 041101 (2020), which is incorporated herein by reference. As an example, an accurate qualitative source can generally provide photon pairs and photon clusters (>2 entangled photons) with 99% fidelity substantially more than 60% of the time in a given time slot. See, for example, Jeffrey H. Shapiro and Franco N. Wong, "On-demand single-photon generation using a modular array of parametric downconverters with electro-optic polarization controls," Opt. Lett. 32, 2698-2700 (2007), which is incorporated herein by reference. Using such a source, it is possible to provide time windows that include repeated time windows that will provide entangled photon pairs at specific locations in the system, and it is also possible to specify that only 1% of the time windows will have an erroneous quantum state (e.g., more than one photon).

[0045] Some embodiments of the entanglement server 204 use a deterministic source of entangled photons, which is generated by a known, predetermined loading or setting of quantum emission states in the source. For example, various configurations of quantum dot sources can be used. See, e.g., Hui Wang, Hai Hu, T.-H. Chung, Jian Qin, Xiaoxia Yang, J.-P. Li, R.-Z. Liu, H.-S. Zhong, Y.-M. He, Xing Ding, Y.-H. Deng, Qing Dai, Y.-H. Huo, Sven Chao-Yang Lu and Jian-Wei Pan, "On-Demand Semiconductor Source of Entangled Photons Which Simultaneously Has High Fidelity, Efficiency, and Indistinguishability", Phys. Rev. Lett. 122, 113602, (2019), which is incorporated herein by reference. See also, for example, Müller, M., Bounouar, S., K. et al., "On-demand generation of indistinguishable polarization-entangled photon pairs", Nature Photon 8, 224-228 (2014), which is incorporated herein by reference. Advantageously, these types of sources can be provided with the ability to index the expected arrival time slots or positions of entangled photon events. In addition, it is possible to provide associated classical data about, for example, the number of indistinguishable events (e.g., identical photon states) that will follow the prepared excitation state, the expected fidelity (dephasing, added background), and other associated classical information about entangled photons that allows these sources to be generally described and incorporated as part of the larger system described herein. The classical information can be labeled as a single entangled photon event or a larger set of events, depending on the source. A feature of the present teachings is that the classical labeling process allows multiple types of sources to be used in the same system.

[0046] In some embodiments, the entanglement generator 204 can use the links 210, 210' to transmit the generated entangled qubits to the nodes 206, 206'. These transmitted qubits can be sent in any (one or more) classical channels embedded in the links 210, 210' or quantum channels separated therefrom, which use various systems and methods for transmitting entangled qubits. The entanglement generator 204 can be electronic and can generate entangled electronic qubits that are transmitted electronically. The entanglement generator 204 can also be optical. For example, the entanglement generator 204 can be an entangled photon source that generates entangled photons. These photons are sent through the links 210, 210' that include optical fibers that transmit entangled photons. These links can also be free space. The nodes 206, 206' include a quantum entangled cache 208, 208' for storing and retrieving entangled qubits at each node 206, 206'. Real systems will appropriately balance the rates at which entangled bits are generated and consumed over a particular coherence half-life of the entanglement.

[0047] The quantum entangled cache 208, 208' may include a mechanism for determining the coherence of the qubits at each node. Coherence is a measure of the degree of entanglement. In some embodiments, this mechanism includes a coherence detector with a certain discarding mechanism. In some specific embodiments, this mechanism has reliable statistical knowledge about the coherence half-life and uses at least one of many different types of error correction coding. The qubit can be discarded after aging (age-out), for example after a known half-life, or alternatively based on aging of known error rates or error conditions. In some embodiments, both mechanisms are used. Some embodiments rely on entanglement purification, which uses a measurement of the number n of adjacent qubits to determine with high probability that a given qubit is entangled. Therefore, various mechanisms can be used to determine the coherence of one or more qubits that are part of an entangled system.

[0048] The quantum entangled cache 208, 208' also includes a synchronization mechanism that ensures that matched pairs or sets of qubits are used at each node 206, 206'. For example, the synchronization can be associated with a specific known order of qubits in the cache, which is associated or aligned with another order of qubits in another node. In some embodiments, the synchronization mechanism is an ordered cache. In some embodiments, the synchronization mechanism uses classical channel information exchange. For example, the order of qubits in two different nodes can be exchanged and updated as the order changes. Moreover, in some embodiments, the nodes are connected via a communication channel 212 that can support one or both of quantum communication and classical communication. This channel 212 can be the same or different from the link 210, 210' that transmits photons to the cache 208, 208'.

[0049] Figure 3 A block diagram of an embodiment of a cache of quantum entanglement in accordance with the present teachings is illustrated. Qubits are supplied to a qubit loader 302 from a quantum channel 304 and / or a combined quantum-classical channel 306. The supplied qubits are entered into a qubit repository 308, which is a quantum repository. The qubit repository 308 is a physical storage system that retains and maintains the entanglement and coherence of the ordered qubits to a predetermined acceptable degree. Thus, the qubit repository 308 generally accepts the qubit state from the loader 302 into a physical mechanism that can maintain the coherence and entanglement of the qubits in an ordered manner so that the unloader 310 can access the state and supply the state to an application 312. The qubit repository 308 is stored in a qubit repository 308. Figure 3308 is shown as a first-in-first-out (FIFO) structure such that the youngest qubit (to the cache) is located at the bottom slot 314 of the qubit repository 308, while the oldest qubit is located at the top slot 316, so that the oldest qubit will be available next for application 312. It should be understood that the terms "top" and "bottom" are relative terms used to describe the present teachings, but may or may not represent an actual qubit storage system. For example, one skilled in the art will recognize that the qubit repository 308 can be implemented in a variety of ways, such as with a simple fiber optic delay line, where a photonic qubit enters the delay line and will first leave the delay line in order to be used by an application connected to the repository. In various embodiments, the qubit loader 302 and / or the qubit unloader 310 may include, for example, a passive coupler / splitter, a quantum switch, an optical switch, a quantum wavelength converter, a quantum repeater, and / or a quantum state converter.

[0050] The present teachings contemplate various types of storage systems. Various embodiments of the qubit storage library 308 can have various physical implementations and operations. This includes, for example, fiber loops, including layered fiber loops, which can implement various input-output relationships between loaded photon qubits and unloaded photon qubits. For example, FIFO, last-in-first-out (LIFO), or other cross-access architectures can be implemented. In addition, various types of memory devices (such as ion- or atom-based memory devices) are suitable for use as random access memory devices because time slots can be associated with positions on, for example, a lattice or other ordered physical arrangement that supports a particular quantum system. For example, a time slot may be associated with the position of a nitrogen vacancy in a diamond lattice. Therefore, the quantum entangled cache of the present teachings is compatible with a variety of storage structures, including random access storage structures and stack-type storage structures (such as FIFO and LIFO).

[0051] Classical data loader 318 retrieves data from classical channel 320 and / or optionally from combined classical-quantum channel 306. Classical data loader 318 loads data associated with a particular qubit into a classical repository 322, which holds and maintains the classical data associated with the particular qubit. Classical repository 322 is a conventional computer memory that may be a volatile or non-volatile memory, which may take a variety of forms well known in the field of computer hardware. Data unloader 324 may provide the classical data associated with a particular qubit to application 325, so that the application can then effectively use any subsequent information about the state of the qubit in the application. Subsequent information includes, for example, information obtained by processing qubits in a quantum logic element, performing state collapse-inducing (non-singleton) measurement operations on qubits, and / or measurements on qubits that do not collapse the qubit state, but instead provide information about the state of the qubit or other qubit characteristics. Thus, one aspect of the systems and methods of the present teachings is that the quantum entangled cache 300 holds and maintains classical data associated with qubits and provides this data to higher level applications to assist in application processing of the qubits.

[0052] The quantum entangled cache 300 includes a fidelity system 326 connected to the quantum storage repository 308 and the classical storage repository 322. The fidelity system 326 can identify and remove or otherwise reject bad qubits, such as bad qubits in time slots 327. For example, this will include qubits that have collapsed or are about to collapse and / or have lost certain predetermined fidelity, entanglement, and / or coherence properties. The fidelity system can mark the bad qubit to notify the user that it is bad. It should be understood that the fidelity system 326 and the associated configuration of the quantum cache 300 can be configured to operate with a group of qubits and not necessarily operate at a single qubit-by-qubit level in a deterministic manner. That is, a group of qubits representing a single qubit state is expected, and the qubit state is represented by a measurement of the whole. In these systems, a predetermined fidelity level will be expected based on the whole. Fidelity, entanglement, and / or coherence properties can be non-deterministic and represented by probability and / or other statistical measures.

[0053] Quantum purification techniques may be applied to these collections via a fidelity system 326. In general, the fidelity system is responsible for maintaining a qubit or collection of qubits in a repository at a known good fidelity level so that that qubit state can subsequently be provided to an application 312, and is also responsible for updating the associated classical data and information about the fidelity for that qubit as needed. The fidelity system 326 may physically remove bad qubits from the repository, or prevent bad qubits from being unloaded and / or subsequently used based on the associated classical data information.

[0054] In some embodiments, qubit unloader 316 is connected to application 328. The application may include a quantum measurement system (not shown). In these embodiments, the quantum measurement system determines the state of a qubit in the qubit unloader, and this state value is used by the application. For example, the state value may be the same as the state value determined by a measurement of another qubit in a remote cache, where the other qubit in the remote cache is entangled with the qubit in the qubit unloader.

[0055] In some embodiments, application 328 includes a quantum processor system (not shown) that uses the stored quantum state information. The quantum processor may include various quantum logic elements that perform unitary and / or non-unitary transformations on the quantum state. For example, CNOT, Hadamard, and / or Pauli-Z / or Pauli-X / or Pauli-X and Pauli-Z and / or measurements that may be performed by application 328.

[0056] In some embodiments of the systems and methods of the present teachings, qubit unloader 310 and data unloader 324 are connected to an optional communication channel 330 via application 328. Channel 330 may support one or both of quantum communication or classical communication via separate or combined channels. Channel 330 allows application 328 to connect separate quantum entangled caches 300 together to share either quantum information or classical information. Channel 330 may be used to exchange qubits directly from a qubit unloader in one or another separate quantum entangled cache and / or qubits processed by quantum logic elements connected to the channel and a qubit unloader 324 in one or another quantum cache.

[0057] Figure 4 An embodiment of a table 400 showing a cache structure of a quantum entangled cache according to the present teachings is illustrated. The cache structure shown in table 400 includes fields for both classical information and quantum information. For example, an index field and an age field are provided. The index associates a specific item of classical data (e.g., various metadata) with a specific quantum state in a plurality of quantum states. There are also fields for describing which nodes hold the qubits with which the qubits are entangled. There may be fields for other parameters, such as the type of qubit, the half-life of the qubit, the qubit error rate, the qubit access time, and other parameters. Fidelity information may be included. The classical information is tagged, in other words, indexed to a specific qubit residing in the cache, and is also maintained and updated as needed when the qubit is stored in the cache.

[0058] Another feature of the system and method of the present teachings is that it accommodates the fact that qubits generated from different physical representations have different properties and provide different parameters that can be part of classical information. For example, some physical qubits can be stored for a long time, some physical qubits preserve entanglement longer than other physical qubits, some physical qubits are easy to access and use, while other physical qubits require more complex and time-consuming access schemes. These different physical qubit representations can have different associated classical information that is applicable to the physical properties of those specific qubit representations. The quality of different physical qubits can affect the design of the cache. As an example, some embodiments of a quantum entangled cache according to the present teachings use a hierarchical cache system.

[0059] Figure 5A A schematic diagram of an embodiment of a multi-layer quantum memory 500 according to the present teachings is illustrated. The multi-layer quantum storage library 500 has a top layer 502 and a bottom layer 504. In this example, the top layer 502 represents a storage system with a relatively fast access time but a relatively short storage time, wherein the bottom layer 504 represents a storage system with a relatively slow access time but a relatively long storage time. In some embodiments, the top layer 502 may be a fiber loop buffer storage system that holds photon qubits. These photon qubits may be single photon qubits, frequency entangled photon qubits, or may be polarization-encoded qubits. In some embodiments, the bottom layer 504 is an atomic qubit storage system. This bottom layer 504 may include any of a variety of known atomic qubits. The top layer 502 is used first. This is because the top layer 502 provides low-latency access to the qubits, although the qubits remain entangled for a shorter time. The bottom layer 504 is used in situations where the system can support higher latency access. In some embodiments according to the present teachings, when time permits, the bottom layer transfers the qubits to the top layer, thereby optimizing the trade-off between latency and entanglement half-life for a particular application. The bottom layer qubits remain entangled for a longer time. For example, photon qubits are generally difficult to retain for a long time, but are easy to access, so the access latency is low. Atomic qubits can maintain entangled states for longer periods of time; but the access latency is higher. Photons are also generally abundant resources, while atomic qubits are not as abundant. The multi-layer quantum storage repository 500 of the present teachings appropriately manages and allocates physical qubits based on their individual characteristics. Therefore, a key benefit of the quantum caches of the present teachings is that they provide a mechanism that allows classical systems to efficiently utilize quantum states and / or quantum properties from different quantum physical systems with a common interface and / or representation.

[0060] Various known fiber buffers can be used to short-term store, delay, or buffer photons carrying quantum states. For example, fiber loop buffers, various optical cavities such as fiber Bragg cavities, slow light systems. Various nonlinear (e.g., four-wave mixing) schemes can be used to produce various short, long, and / or controllable delays of (one or more) quantum photons passing through the optical fiber. Importantly, for the systems and methods of the present teachings, various known properties of fiber buffers (active and passive) produce predetermined delay characteristics of the buffer, and therefore are obligated as part of the classical information to be marked with one or more of the photons input to the buffer.

[0061] Fiber buffers are particularly suitable as the top layer 502 of a quantum storage system. As an example, in some embodiments of the present teachings, the top layer 502 of the physical storage system includes a fiber buffer with an adjustable delay. See, for example, Stéphane Clemmen, Alessandro Farsi, Sven Ramelow, and Alexander L. Gaeta, "All-Optically Tunable Buffer for Single Photons", Opt. Lett. 43, 2138-2141 (2018), which is incorporated herein by reference. One feature of such a buffer is that the input pump laser wavelength produces a delay of the quantum encoded photons. For example, a delay range of more than a few nanoseconds can be deterministically achieved by tuning the pump wavelength across a certain wavelength range. Therefore, specific (and variable) delay information can be included in the classical information associated with the qubits in these kinds of short-term fiber buffer memories. Another feature of such a buffer is that the bandwidth of the optical photons input to the buffer determines the delay. As such, the classical information associated with the known input spectrum of the quantum encoded photons provides information about the delay achieved in the short-term storage library.

[0062] In addition to short-term storage repositories (e.g., fiber buffers), various known atom- and ion-based systems can be used to construct quantum storage repositories that store quantum state information according to the present teachings. In addition, quantum information can be transferred from photon states to electronic states of atomic and ion systems. That is, quantum states carried by photons can be stored in electronic states in various ions and atoms to realize these longer-term quantum storage systems and also read out of the system as photons and detected. Quantum states stored in atom- and ion-based memories can also be read (measured) directly in the electronic domain.

[0063] There are many known protocols for implementing quantum atomic memories, including, for example, electromagnetically induced transparency (EIT), reversible inhomogeneous broadening (CRIB), and atomic frequency comb (AFC), which can be used for quantum caches according to the present teachings. See, for example, Heshami K, England DG, Humphreys PC, et al., "Quantum memories: Emerging Applications and Recent Advances", J Mod Opt. 63, 2005-2028 (2016), which is incorporated herein by reference. Although this situation is expected to change as technology develops, it is generally believed that losses in fiber-based buffers will limit storage times to tens of microseconds. On the other hand, atomic systems, especially cold atomic systems, can maintain quantum states on time scales of seconds or longer. These numbers are illustrative only and are not intended to limit the present teachings in any way, but they are used to illustrate that different layers of cache are needed to support a wide range of storage and access times.

[0064] Atomic memories are particularly suitable as the bottom layer 504 of quantum storage systems because they generally exhibit longer storage times. As an example, in some embodiments of the present teachings, the bottom layer 504 of the physical storage system includes an optical quantum memory based on cold atoms. See, for example, Y.-W. Cho, GT Campbell, JL Verett, J. Bernu, DB Higginbottom, MT Cao, J. Geng, NP Robins, PK Lam and BC Buchler, "Highly Efficient Optical Quantum Memory with Long Coherence Time in Cold Atoms", Optica 3, 100-107 (2016), which is incorporated herein by reference. One feature of this memory is that it absorbs photons efficiently and also has low decoherence. In these systems, optical quantum states are loaded into a cold atomic gas prepared by an applied magnetic field gradient, so that the spectral components are encoded on the gradient. The controlled reversal of the applied magnetic field generates a photon echo from the gas, which represents the quantum state of the input optical photon. In these systems, the storage time is a function of the input control pulse duration. The ability to cool the gas affects the decoherence time. Therefore, the known and controllable parameters of the memory implementation (e.g., optical control power and optical bandwidth, applied magnetic field, readout pulse energy bandwidth, etc.) are directly related to the memory quantum performance metrics (such as storage time, readout time, decoherence, etc.). Regardless of the specific atomic memory protocol, it is therefore possible to label the stored quantum state with associated classical information, which allows the quantum cache system to be controlled independently of the specific physical implementation of the memory.

[0065] It should be understood that the quantum storage physical systems described herein are only some possible specific examples of quantum storage repositories that can be used in the methods and devices of the present teachings. Based on the specific characteristics and protocols of the physical storage system, various known quantum optical buffers and memory schemes have specific classical information associated with the characteristics of the stored quantum bits. For example, operating parameters such as delay, memory depth, storage time, loading delay and / or unloading delay can be marked. In addition, various damages can also be marked, such as various losses, decoherence mechanisms, phase shift effects, additional backgrounds, and various other nonlinear damages that affect quantum states. In addition, as the systems and methods for physical quantum storage mature, the types of classical information will change and grow. The method and device of the present teachings are characterized by the use of an abstraction layer that adapts to the expected changes and maturity of the underlying physical system. Therefore, the embodiments of the multi-layer quantum storage 500 can be used not only with some of the example physical systems provided herein, but also with other known and future physical quantum storage systems. In other words, the present teaching is not limited to a specific type of quantum storage system.

[0066] Figure 5B An embodiment of a cache 550 including a physical structure with metadata for a cache of multi-layer quantum entanglement according to the present teachings is illustrated. The cache 550 includes both software / information and hardware. There are quantum elements 552 and classical elements 554. The fidelity system includes a quantum coherence engine 556 connected to physical qubits in a long-term quantum repository 558 and a short-term quantum repository 560. The physical qubits in the long-term quantum repository 558 can be, for example, atomic qubits in an atomic memory. The physical qubits in the long-term quantum repository 558 can be electromagnetically induced transparent atomic quantum memories. The physical qubits in the long-term quantum repository 558 can be any of a variety of other known long-term quantum memories. In various embodiments of the methods and devices of the present teachings, the long-term memory has a half-life of nominally tens of microseconds, milliseconds, seconds, or tens of seconds. The physical qubits in the short-term quantum repository 560 can be, for example, photon qubits in a fiber loop memory. The physical qubits in the short-term quantum repository 560 can be single nitrogen vacancy center quantum memories. The physical qubits in the short-term quantum storage reservoir 560 can be any of a variety of other known short-term quantum memories. Moreover, in various embodiments of the methods and apparatus of the present teachings, the short-term memory has a half-life of nominally nanoseconds to microseconds. Other important factors in selecting a quantum memory system include, for example, readout mechanism, quantum fidelity, storage efficiency, time-bandwidth product, stability, and noise, just as some specific examples.

[0067] The quantum coherence engine 556 uses purification or some other non-measurement monitoring technique to check the qubits in the short-term and long-term storage libraries 558, 560 to interrogate their coherence levels. This all happens on the quantum side of the cache 552. When the coherence engine 556 decides that a qubit is bad, it then notifies all other caches sent to the entangled qubits over the classical channel so that those nodes do not use those qubits. The cache 550 uses the entanglement graph information 562 in the classical part 554 of the cache 550 to determine which nodes must be notified of the qubits that have timed out.

[0068] In some embodiments, when a qubit is retired due to exceeding its lifetime, the entire cache is popped like a stack in a processor. The qubit at the top is the oldest and most likely to go bad, but if something in the middle of the cache times out or is determined to be irrelevant or entangled, the qubit below it is moved up (popped) one step. When a qubit is pulled from the cache and measured as part of any algorithm, that qubit becomes stale. All other node caches need to know this information as well. Each cache can determine this information on its own by, for example, independently measuring the lifetime, or in some embodiments this information can be provided to the cache, as in the case of expired or timed-out qubits, a classical channel communication protocol process is used for this notification. In the stack model, you only need to stay in sync with the index number in index column 564, because you know that the qubit is moving towards the top of the stack.

[0069] In some embodiments, once qubits reach a predetermined age threshold T, the probability that they lose coherence is relatively high. A classical age timer keeps track of this time and can automatically remove aged qubits. The T value for each qubit is retained in the aging timer 566 column of the cache to be associated with each qubit or group of qubits of the same type. This is the classical portion 554 of the cache 550. There can be two physical age timers, for example, one for the long cache and one for the short cache. This is useful in some systems because long atomic caches may have a longer half-life. The advantage of using an age timer is that if all nodes agree on the timing parameters, then messages are unnecessary and classical communication is not required to indicate whether a qubit has gone bad (what is lost is the quantum state information). In these specific examples, all nodes are synchronized and will remove aged qubits at the same and / or appropriate times.

[0070] In some embodiments of methods and apparatus according to the present teachings, everything stays in the long term repository 558 until it is near the top of the stack. Then, the qubits are moved to the short term repository 560 so that they are available for immediate use. Then, if the qubits stay in the short term repository 560 for too long, the age timer will go off and they will be discarded, and a classical message will be sent to notify other nodes to move up the appropriate stack.

[0071] Another feature of the quantum caches of the present teachings is that they can be used in conjunction with many networking applications. Figure 3 , numerous applications 328 running on multiple nodes in the (various) network may receive qubits for application 312 and / or associated classical data for application 325 from quantum repository 308 and / or classical repository 322 in each node. Some example multi-node applications are described below.

[0072] Fig. 6A An embodiment of a bus network 600 using an entangled cache in accordance with the present teachings is illustrated. Bus network 600 is just one specific example. It should be understood that other network architectures can be implemented. A number n of nodes 602, 602', 602" are connected to a classical channel 604. Each node 602, 602', 602" has an entangled qubit cache. The cache is supplied by an entanglement server (not shown). The qubits are organized in pairs between each set of nodes. Thus, node 1 602 has one "column" of qubits entangled with node n 602', and node 1 602 has another "column" of qubits entangled with node 2 602', and so on.

[0073] The use of a quantum cache for addressing is described in conjunction with an Ethernet-like protocol. However, it should be understood that networks using entangled cache addressing in accordance with the present teachings are not limited to this. In the specific example described in conjunction with Figure 6, node 1 602 wants to send a packet to node n 602". Node 1 602 broadcasts a packet that contains an address field on a classical Ethernet channel 604. To determine the contents of the address field, node 1 samples M qubits from the node n column in its cache and generates a random resulting number. Node n 602" has an entangled pair of each of these M qubits in its cache. Node 1 602 sends the sampled result over the classical Ethernet. Node n 602" samples the entangled pair from its cache and generates a resulting random number that will match the random address field from node 1. Node n 602" matches the random number received on the classical channel to know that the packet is for node n.

[0074] All other nodes, such as node 2 602', also sample the M qubits in their qubit caches in the column for node 1 602 to see if the packet is addressed to them. Node 2 602' does not match the random number provided by node 1 602 and received via the classical channel. As such, the measured random number represents the quantum source-destination pair address. The probability that the match is a false match is 1 / E, where E is the error rate described further below.

[0075] Figure 6B A table 650 is illustrated showing the structure of an entangled qubit cache for a multi-node network of the present teachings. In table 650, N is the size of the address space requiring sqrt(N) bits, I = N + E, where 1 / E is the acceptable error probability (rate) requiring sqrt(E) bits. At a given error rate, the total number of qubits required for the total address space = sqrt(I).

[0076] Combination Fig. 6A The operation of the entangled quantum cache in the nodes 602, 602', 602" described in -B is based on an addressing application, but many other applications can use shared entanglement in a network configuration according to the present teachings. Additional application examples are provided herein.

[0077] Figure 7A block diagram of an embodiment of a quantum-enabled information system 700 using an entangled quantum cache 702 according to the present teachings is illustrated. Entangled qubits are supplied to the quantum cache 702 from an entanglement server 704 via a quantum portion of a communication channel 706. The quantum cache 702 supplies ordered and labeled entangled qubits to an application 708. The quantum cache 702 may also supply the application 708 with associated classical information about a particular associated ordered labeled qubit. The quantum cache 702 is controlled by a processor 710. The processor 710 controls a fidelity system 712, a qubit loader 714, and a classical data loader 716 in the quantum cache 702. The processor 710 also controls a classical repository 718 and a quantum repository 720 in the quantum cache 702. The processor 710 communicates with the application 708 so that it can command a quantum unloader 722 and a classical unloader 724 to supply entangled qubits and associated classical data to the application 708 at a desired time. The desired time can be selected to ensure that the entangled qubits supplied at two different nodes share an entangled state, thereby allowing two remote nodes to share relevant state information. The desired time can be on demand. The desired time can be predetermined. The desired time can be based on the lifetime of the quantum state. The desired time can be based on the time to generate the quantum state. The desired time can be based on application requirements. For example, the application in various embodiments can access a specific shared entangled state. Moreover, for example, the application in various embodiments can access a specific type of quantum state. Moreover, for example, the application in various embodiments can access a specific basis of the quantum state. Moreover, for example, the application in various embodiments can access a specific fidelity of the quantum state. Moreover, for example, in various embodiments, the application can access the quantum state based on at least one of the entanglement characteristics, the basis of the quantum state, the fidelity of the quantum state, the arrival time of the quantum state, the source of the quantum state, the age of the quantum state, the half-life of the quantum state, the birth time of the quantum state, the flight time of the quantum state, and / or the type of the quantum state.

[0078] Figure 8 A block diagram of an embodiment of an application system 800 utilizing an entangled quantum cache 802 interacting with an application 804 in accordance with the present teachings is illustrated. A processor 806 sends and receives application commands to the application 804. The processor 806 sends quantum cache management commands to a quantum storage repository 808. The processor 806 also sends classical cache management commands to the classical storage repository 804.

[0079] Some embodiments of the present teachings utilize an abstraction layer that supports an easy-to-use interface for application codecs. This is called the Classical Application Interface (CAPI). The abstraction layer translates between the CAPI and the quantum system. The abstraction layer uses, interprets, and / or generates at least some of the classical data associated with the quantum state.

[0080] The quantum mechanical nature of quantum devices adds another level of complexity to the underlying behavior of the devices that provides useful quantum functionality for information systems engineering. Most engineers and scientists are trained in basic programming of causal Newtonian systems. For reference, there are approximately 1,600 quantum physicists worldwide, but there are over 20 million software professionals worldwide. In order for quantum mechanical systems to be widely adopted, they must be easily usable by classically trained software professionals. Classical application interfaces translate between these worlds. The advantage of CAPI is that it allows any codec to apply quantum systems as a black box. Codecs do not have to know how the quantum system works, only how it behaves. CAPI appears to software developers as a familiar function structure in their programming language of choice. Below are some examples that illustrate CAPI and how it works in an entangled quantum cache with application interfaces. These examples are illustrative and not comprehensive.

[0081] The cache_pointer identifies a specific quantum cache 808, allowing multiple caches to be used in a single node. Figure 8 Only one node is shown in the diagram, but it will be appreciated that the present teachings apply to any number of nodes. Qubitpointer identifies a specific qubit in the cache and its associated metadata. Node identifies a specific node. Channel (not shown) allows multiple connections from a single node.

[0082] The cache management functions include: 1) Integer = Get_Qubit_Count (cache_pointer), which indicates how many qubits are in the cache; 2) Integer = Get_Long_Term_Qubit_count (cache_pointer), which indicates how many qubits are long-term qubits; 3) Integer = Get_Short_Term_Qubit_count (cache_pointer), which indicates how many qubits are short-term qubits; 4) Random lnteger = Sample_Qubit(cache_pointer, qubit_pointer), which indicates the sample / collapse to classical; 5) Time = Get_Qubit_Age(cache_pointer, qubit_pointer), which indicates the age of the qubit; 6) Array(n) = Get_Qubit_Entanglement_Map(cache_pointer, qubitpointer), which indicates which qubits are entangled; and 7) Localcachepointer = Put_Entangled_Qubit(cache_pointer, qubit_pointer, node), which puts the entangled qubit on another node. This function puts one member of an entangled pair on another node. It should be understood that the specific calls associated with the cache management functions are presented for illustrative purposes and are not intended to limit the present teachings in any way.

[0083] In general, an application system 800 utilizing an entangled quantum cache 802 interacting with an application 804 will include a processor 806 capable of sending and receiving application commands to the application 804 that is easy to use for conventionally trained software engineers and software developers. For example, the abstraction layer limits the amount of detailed information required to control the quantum storage repository 808 and the classical storage repository 810 that is passed to the application commands generated by the application 804, as shown in the examples provided herein.

[0084] In one specific example, application 804 is combined with Fig. 9 The description of is described in more detail in the quantum private address application. In these embodiments, the application command includes Secret Address = Get Address (node ​​X), which indicates what the random classical private address appears to other nodes.

[0085] In other specific embodiments, application 804 is an ultra-dense codec application, which is described below in conjunction with Figure 10-12The description of is described in more detail. In these embodiments, the application command includes: 1) Send (transmit_data, channel_number), which indicates sending; 2) Receive_Data = received (channel_number, node), which indicates receiving; 3) Integer = Get_Entangled_Count (node_address), which indicates checking the cache depth; 4) Allocate_Quantum_Channel (percent, channel_number), which allocates the percentage of the channel for sending quantum bits.

[0086] An embodiment of a classical application interface for an ultra-dense codec application would include the following commands. For the sender: 1) Establish_Link(5,10), which commands sharing of entangled qubits between the sender and the receiver; and 2) Send("Hello",5,10), which commands that "Hello" be sent. For the receiver, the commands include: "Hello"=received(5,10), which indicates that "Hello" was received. For the processor, the commands include: 1) 107 = Get Entangled Count (10), which indicates that we only have 107 entangled qubits left, so more channels need to be allocated to exchange entangled qubits; 2) Allocate_Quantum_Channel (50, 10), which allocates 50% of the channels to build the entangled cache; 3) 1025 = Get_Entangled_Count (10), which indicates that we now have 1025 qubits; and 4) Allocate_Quantum_Channel (5, 10), which reduces the allocation to 5%.

[0087] One feature of the entangled quantum caches of the present teachings is that they can support a variety of classical, semiclassical, and pure quantum applications. Several example applications are provided below.

[0088] One application supported by the quantum entangled cache of the present teachings is to provide shared node metadata for distributed information systems. In this application, the qubits in the entangled qubit cache provide metadata for one or more of a variety of different classical distributed information systems. The shared node metadata provided by the quantum entangled cache of the present teachings can support a variety of protocols that can provide, for example, addressing, timing, location and other information shared between pairs of nodes and / or groups of nodes.

[0089] Fig. 9An embodiment of a distributed system 900 that uses an entangled cache to provide shared node metadata of the present teaching is illustrated. A communication channel 902 connects multiple nodes 904, 906, 908, 910. The communication channel 902 supports both quantum communication and classical communication by any of a variety of means. In this embodiment, pairs of M entangled qubits are stored in caches in various nodes. For example, as shown by diagram 912, nodes A 904 and B 906 share M entangled qubits. As shown by diagram 914, nodes A 904 and X 908 share M entangled qubits. As shown by diagram 916, nodes X 908 and Z 910 share M entangled qubits. The various sets of these M pairs of qubits are appropriately labeled and stored in a cache (not shown) in each node 904, 906, 908, 910 so that they can be accessed by the processor in the node 904, 906, 908, 910 for processing and / or measurement to implement the desired protocol. The various M entangled qubits may be distributed by an entanglement server (not shown) over the communication channel 902 or by different means. Some protocols will exchange raw or processed qubits from the cache over the communication channel 902, but other protocols will not require any exchange of qubits to operate.

[0090] Packet 918 includes a quantum address and data. In some embodiments, a quantum address is a random number generated by a sender node and received by a potential recipient node. The random number represents a quantum source-destination pair address. The recipient node measures the qubits entangled with a particular node to generate a random number representing a source-destination address pair for those particular nodes. For example, the qubits entangled with node A are measured by the node to determine whether a received packet is from node A. If the random number in the quantum address of packet 918 matches the random number generated by the measurement of the entangled qubits in a particular receiving node, then the data in the packet is for that receiving node.

[0091] The following is an example of a metadata exchange between node A 904 and node B 906. Node A 904 measures each of the M qubits known to be entangled with node B and generates a random number representing an address. This random number is sent classically in the quantum address field of packet 918 along with some data. Node B 906 measures each of the M qubits known to be entangled with node A 904 to generate a random number. Node B 906 receives packet 918 and compares the received random number to the generated random number. If there is a match, then the data is from node A 904 for node B 906.

[0092] Another feature of the present teachings is that quantum metadata generated using methods and apparatus according to the present teachings can be used to prevent anyone from knowing which source-destination pair of nodes is addressed using a quantum key distribution assurance level. This is because the cache of quantum entanglement enables two or more nodes to share a random number "secret" without exchanging any classical data.

[0093] In general, this feature can be applied to any of a variety of addressing schemes. For example, an address can be one or more of a network address, a memory location, a database index, a geographic address, a telephone number, and many other identifiers. Any entity that wishes to place data on or communicate with any other entity possesses a number n of entangled qubits, with associated other paired entangled qubits possessed by other entities. The number n is typically chosen to be large enough to minimize address conflicts.

[0094] An example addressing scheme according to the present teachings is to apply quantum metadata to quantum Ethernet (broadcast channel), where the addresses are entangled qubits, such as Fig. 9 As described above. In this addressing scheme, if node A 904 has a packet for node B 906, node 904 encodes with N superimposed qubits that are ordered and entangled with the qubits in node B 906. The packet includes the quantum address and data from node A 904. Everyone receives the packet. Before measurement, nodes 904, 906, 908, 910 do not know their specific addresses. When the nodes make a measurement, they generate a random number. Node A 904 then sends the random number to all nodes 906, 908, 910 via classical broadcast. If the random number is consistent with the random number generated in the node when the measurement was made, then the packet is for that node. Therefore, the random number represents the quantum source-destination pair address.

[0095] A feature of this approach is that an eavesdropper cannot determine to which node the data is directed, nor can an eavesdropper determine the node that transmitted the data. Random number broadcasts generally do not reveal any information other than the source and destination pair of the shared data. If the quantum entangled pair is manipulated by a third party that is measured and / or deceived, then these measurements and / or deception actions can be detected using a quantum key distribution protocol between the entanglement server and the cache. In other words, if someone attempts to determine the source destination pair, or deceive the source and / or destination, then that action will destroy the correlation of the random numbers. This feature makes the addressing scheme absolutely private to deception, which is very desirable for many applications.

[0096] As another example of an address according to the present teachings, consider a simple three-node network including one sender and two receivers. For example, this three-node network includes Fig. 9Nodes A 904, B 906, and Node X 908. Unlike the determinism in the classical addressing scheme of the prior art, the addressing scheme according to the present teaching is similar to a hash collision. However, if the number of qubits M in the cache is much larger than the address space, then the probability that the node will send data to the wrong entity is very small. For a three-node network, each node has only one entangled qubit, and the qubit can eventually be measured as 0 or 1 with a probability of 50%. Using five qubits to handle two addresses, the chance of all three nodes getting the same random number is very small, (1 / 2) 5 To obtain, for example, (1 / 10) 7 If the address error rate is 20+n qubits, then 20+n qubits are needed, where n represents the address space covered. Using twenty-one qubits yields (2,000,000) -1 error rate, and using twenty-two qubits to generate (4,000,000) -1 The error rate of , and so on. In this way, the number of qubits used per address can be significantly larger than the number of classical address bits.

[0097] In general, the quantum entangled cache system and method of the present teaching allows nodes to share entangled qubits between any other nodes they need to communicate with. In various embodiments, data is broadcast classically, or it can also be sent on a quantum channel. As described above, the entanglement can be N-way entanglement, and M qubits are fed directly from a single server to the N cache. The entanglement of M qubits can include K dimensions. Quantum key exchange can be used to protect data and / or encrypt data by known classical means. Address information is provided by measuring the selected qubits in the quantum entangled cache. The sender makes a measurement and generates a random number, which is broadcast together with the data. The receiver also measures the selected qubit to generate a random number and compares the number with the number received in the address of the group on the network. When the two random numbers match, it can be concluded that the data is for that node.

[0098] In a network with n nodes participating in such a scheme, each node requires a set of pairs of qubits entangled with every other node. Each sender selects one of those pairs to address the desired node for communication. In some embodiments, each node requires 2 (n-1) The receiver needs to measure each of these pairs of entangled sets to match the sender's address sent classically. And each set needs to have at least n qubits.

[0099] In some embodiments, the receiver can make the measurement one bit at a time. So, for example, the first bit broadcast is compared to the first qubit in each set. Statistically, this should eliminate 1 / 2 of the potential senders. Then the second qubit, which eliminates the next 1 / 4, and so on. In this way, the receiver only needs to make n+(n-1)+(n-2)+.....=2n(n-1) comparisons. The probability that the receiver misidentifies a message not intended for the receiver is 1 / 2 n As the address space increases, the probability of a message being misidentified decreases. The error rate in addressing can be further reduced by increasing the address space, which makes the address space more sparse. For example, for 2 m Nodes use 2 n The address space is such that n>m, and each additional bit of addressing reduces the error rate by 1 / 2.

[0100] A feature of this teaching is that the recipient actually obtains two pieces of information by executing the protocol. First, the recipient knows that the message is for that specific reception. Second, the recipient knows the address of the source of the information.

[0101] Some systems according to the present teachings can be used for network initialization in the following manner. The scheme is used to develop a set of classical addresses, which are the result of a measurement broadcast. These classical addresses appear to be random numbers to everyone except the intended recipient. Thus, the sender sends a classical packet with an address header that is actually a random number determined by this scheme. The receiver learns to use classical logic to find that number, which is actually equivalent to the source and destination addresses, but appears random to everyone else.

[0102] Another feature of this teaching is that it is possible to trade security for addressing overhead. In some embodiments of this teaching, nodes decide how often to refresh addresses (reinitialize) based on security needs. For extreme security, the address is refreshed for each packet. Less secure implementations only refresh at selected time intervals, just like updating a password.

[0103] Also, some systems according to the present teachings use an addressing system that uses a cache of quantum entanglement as described herein that provides privacy by starting with a shared secret. Each node pair, also called a source-destination pair, shares a secret upon initialization. The secret is an M-bit number, where the M bits are the size of the address space. It is important to note that this is for pairs of nodes, not for individual nodes. For each pair that wants to have a private source-destination address, an M-bit number must exist. Again, referring to the use of Fig. 9In the distributed system 900 of entangled caches, when node A 904 wants to talk to node B 906, node A 904 measures M qubits entangled with the M qubits in the cache of node B 906. Node B 906 also measures M qubits entangled with the M qubits in node A 904.

[0104] Node A 904 then performs a bitwise classical exclusive-OR (XOR) of the value of the measured qubit with the shared secret and sends the result of the XORed sample classically to node B 906 over channel 902. Only node B 906 has the shared pairwise secret. Node B 906 performs the same XOR operation on the value of the measured qubit, so it is looking for the same number that still looks random. Other nodes, such as node X 908, do not have the pairwise secret and therefore cannot do anything with the quantum address. If node X 908 or another node is somehow able to capture the entangled bits destined for node B 906, then they cannot forge the identity of node A 904 because they lack the shared secret to perform the XOR.

[0105] In some methods according to the present teachings, quantum secret tumbling is used to refresh keys in the following manner to prevent having static keys (or secrets). At any time, a node pair (e.g., node A 904 and node B 906) can enter their corresponding entangled caches and sample again (i.e., perform a measurement on the M qubits in the cache). In some embodiments, this process occurs after each message. The measurement result (sample) can be XORed with the original secret. The result can become a new or tumbled secret, which can be used for subsequent messages. This new or tumbled secret can also be called a quantum signature and is an aspect of the present teachings.

[0106] Another application of a quantum entangled cache system according to the present teachings is the implementation of quantum super-dense coding. Super-dense coding is a powerful quantum communication scheme that allows a two-fold increase in transmission capacity compared to classical communication channels. This is because two classical bits of information can be sent using one qubit. The quantum cache according to the present teachings is used as a local resource for implementing super-dense coding protocols.

[0107] Fig.10An application 1000 of a known quantum ultra-dense encoding and decoding scheme operating between a sender 1002 and a receiver 1004 is illustrated. Two classical bits of information are sent by a sender 1002 (whom we will call Alice for simplicity) to a receiver 1004 (whom we will call Bob for simplicity). These information bits 00, 01, 10, 11 are encoded and decoded on one of a pair of entangled qubits, which are prepared in Bell states by a qubit source 1006. One entangled qubit is provided to the sender 1002 by the source 1006 and modulated with one of the four classical information bits and then sent to the receiver 1004. Another entangled qubit that is not modulated is provided to the receiver 1004 by the source. By processing the modulated qubit and the other entangled qubit, the receiver 1004 is able to determine which of the four information bits was sent by the sender 1002. Source 1006, sender 1002, and receiver 1004 use operators such as quantum CNOT 1008, Hadamard 1010, and / or Pauli-Z / or Pauli-X / or Pauli-X and Pauli-Z 1012. Receiver 1004 uses measurement 1014 on the modulated qubit from sender 1002 and the other qubit of the entangled pair provided by source 1006 to decode the classical information.

[0108] Fig.11 An embodiment of an ultra-dense encoding and decoding system 1100 using an entangled cache according to the present teachings is illustrated. The sender 503 and the receiver 505 can operate as described above in conjunction with FIG. 5 . A cache 1104 is connected to the sender 503, and another cache 1106 is connected to the receiver 505. The caches 1104, 1106 are connected to the entanglement server 1102. In some embodiments, this connection is provided by a quantum link 1108, but it should be understood that many other connection means can also be used. The caches 1104, 1106 are supplied with entangled qubit pairs by the entanglement server 1102. The entanglement server fills the caches 1104, 1106 with entangled qubits. The caches 1104, 1106 tag each qubit with appropriate associated classical information and maintain the qubit in an entangled state as described herein. In this way, the sender cache 1104 and the receiver cache 1106 are filled.

[0109] Each information bit modulated by sender 503 includes a qubit pulled from the cache. Each information bit decoded in receiver 505 uses the received modulated qubit sent from the sender through quantum channel 1110, which is processed as described in conjunction with FIG5 using qubits pulled from cache 1106. The receiver uses the classical information tagged to each qubit in cache 1106 to determine which qubit to pull and process with the modulated qubit.

[0110] In some embodiments, sender 503 applies operators to qubits in sequence and sends them to receiver 505 via quantum channel 1110. These operators are I:00, X:01, Z:10, and XZ:11. Receiver 505 performs CNOT operations on cached qubits from cache 1106 and qubits received from sender 503 in sequence. This operation is followed by a Hadamard transform operator that performs a measurement to decode the classical information bit modulated by sender 503. Two bits of classical information are provided via link 1110 using only one qubit resource.

[0111] Fig.12 Another embodiment of an ultra-dense codec system 1200 using an entangled cache according to the present teachings is illustrated. Fig.11 Similar to the ultra-dense codec system 1100 described above, the sender 503 and the receiver 505 operate as described above in conjunction with FIG. 5. In this embodiment, the entanglement server 1202 is connected to the sender cache 1204 and the receiver cache 1206, but has a different architecture than the ultra-dense codec system 1100 described in conjunction with FIG. 6. The caches 1204, 1206 are supplied with entangled qubit pairs by the entanglement server 1202, and the qubits are marked to construct the caches 1204, 1206. The entanglement server 1202 is co-located with the transmission cache 1204 and the sender 503 in an area 1208. The quantum channel 710 connects the transmission area 708 to the receiver 505. The entanglement server 1202 supplies the entangled qubits to the receiver cache 706 using the quantum channel 710.

[0112] Each information bit modulated by sender 503 includes a qubit pulled from the cache. Each information bit decoded in receiver 505 uses the received modulated qubit sent from the sender through quantum channel 1210, which is processed using the qubit pulled from cache 1206 as described in conjunction with FIG. 5. Receiver 505 uses the classical information tagged to each qubit in cache 1206 to determine which qubit to pull and process with the modulated qubit. Sender 503 applies an operator to sequentially modulate the qubits from cache 1204 and then sends them to receiver 505 through quantum channel 610. Receiver 505 performs CNOT operations on the cached qubits from cache 706 and the qubits received from sender 503 in order. Receiver 505 then performs a Hadamard operation and performs a measurement to decode the classical information bit modulated by sender 503. The result is that two bits of classical information are provided through link 1210 using only one qubit resource.

[0113] In some embodiments, the entanglement server 1202 uses quiet channel intervals to fill a remote cache 1206 at the receiver 505 with entangled qubits. In some embodiments, the sender 503 sends entangled qubits before knowing what data is expected to be transmitted. The sender 503 decides what is expected to be sent and sends only one qubit for every 2 bits of classical data. The other classical "bit" is derived by the receiver 505 using a combination of the transmitted qubit and the entangled qubit that was sent much earlier. The result is communication with non-causal behavior.

[0114] It should be understood that, in conjunction with Figure 11-12 The described ultra-dense codec systems with entangled caches are just some specific examples of the systems and methods of the present teachings. Many other architectures can be embedded in the teachings described herein. In various embodiments, the various elements of the codec systems 1100, 1200 can be remotely located or co-located. The distance between the elements also varies with the specific implementation. For example, in many embodiments of the system according to the present teachings, all or some of the elements can be located in the same backplane, card, box, rack or room. Moreover, in many embodiments of the system according to the present teachings, all or some of the elements can be located in various geographic areas from near to far, including land and space-based locations. The connection channel can be implemented with a variety of photonic and / or electronic means, including wireless and wired channels.

[0115] Although the examples of quantum entangled caches described herein are highly simplified, a cache can include qubits from many entanglement servers that can be used for a variety of different purposes to support different services and processing applications. For example, one or more caches can store one or more types of qubits, including different types of physical qubits, with different entanglement conditions and entanglement partners. Moreover, for example, a cache can provide application access to a specific quantum state at a specific time. Moreover, for example, a cache can provide access to a quantum state to an application based on specific classical data associated with that quantum state and / or at a specific time. The cache can be architecturally designed in a variety of configurations, such as FIFO, LIFO, random access, and combinations of these and other storage architectures.

[0116] Equivalent

[0117] Although the applicant's teachings are described in conjunction with various embodiments, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, as will be appreciated by those skilled in the art, the applicant's teachings encompass various substitutions, modifications, and equivalents that may be made therein without departing from the spirit and scope of the teachings.

Claims

1. A method for privately sharing relevant status information as needed, the method comprising: a) sharing a pair of entangled qubits between two nodes connected by a communication channel, wherein one qubit of the pair of entangled qubits is received by one of the two nodes and the other qubit of the pair of entangled qubits is received by the other of the two nodes; b) storing the one qubit of the pair of entangled qubits received by the one of the two nodes in a quantum cache; c) maintaining entanglement and coherence of the one qubit of the pair of entangled qubits stored in a quantum cache so as to subsequently provide the stored one qubit of the pair of entangled qubits to an application; d) using a quantum key distribution protocol to detect manipulation of the pair of entangled qubits by a third party, thereby ensuring the privacy of the shared correlated state information from eavesdroppers; e) storing classical data in a classical repository, the classical data comprising an index associating a particular item of the classical data with a particular entangled qubit such that the one qubit in the pair of entangled qubits has a first associated index and the other qubit in the pair of entangled qubits has a second associated index; f) providing the stored classical data including the index to the application; g) offloading the one qubit of the stored pair of entangled qubits to the application at a specific time based on the provided stored classical data including the index, so that the application accesses the one qubit of the stored pair of entangled qubits as needed; h) measuring the one qubit of the unloaded stored pair of entangled qubits; and i) Based on the measurements, generating shared relevant state information, the shared relevant state information being private to an eavesdropper. The method according to claim 1 , wherein the shared related state information comprises a shared random number. The method according to claim 1 , wherein the shared related state information includes an address.

4. The method of claim 1 , further comprising determining the fidelity of the coherence of the qubits in the quantum cache.

5. The method of claim 4, further comprising removing qubits from the quantum cache based on the determined fidelity.

6. The method of claim 1 , wherein storing the one qubit of the pair of entangled qubits received by the one of the two nodes in a quantum cache comprises storing in a fiber optic loop.

7. The method of claim 1 , wherein storing the one qubit of the pair of entangled qubits received by the one of the two nodes in a quantum cache comprises storing in a first-in, first-out (FIFO) cache.

8. The method of claim 1 , wherein storing the one qubit of the pair of entangled qubits received by the one of the two nodes in a quantum cache comprises storing in a last-in-first-out (LIFO) cache.

9. The method of claim 1, wherein storing the one qubit of the pair of entangled qubits received by the one of the two nodes in a quantum cache comprises storing in a random access cache.

10. The method of claim 1, wherein the first associated index of the one qubit in the pair of entangled qubits indicates with which other node's quantum qubit it is entangled.

11. The method of claim 1 , further comprising sending an application command from the application to a quantum cache to control the quantum cache. The method of claim 11 , wherein the application command comprises a cache_pointer. The method of claim 11 , wherein the application command comprises a qubit_pointer.

14. A method for privately sharing relevant status information as needed, the method comprising: a) sharing a pair of entangled qubits between two nodes connected by a communication channel, wherein one qubit of the pair of entangled qubits is received by one of the two nodes and the other qubit of the pair of entangled qubits is received by the other of the two nodes; b) storing the one qubit of the pair of entangled qubits received by the one of the two nodes in a quantum cache; c) maintaining the entanglement and coherence of the one qubit of the pair of entangled qubits stored in a quantum cache to subsequently unload the one qubit of the stored pair of entangled qubits such that the unloaded one qubit of the stored pair of entangled qubits is coherent; d) using a quantum key distribution protocol to detect manipulation of the pair of entangled qubits by a third party, thereby ensuring the privacy of the shared correlated state information from eavesdroppers; e) storing classical data including classical information tagged to a particular qubit such that the one qubit in the pair of entangled qubits has associated classical information tagged to the one qubit in the pair of entangled qubits; f) unloading the stored one qubit of the pair of entangled qubits at a desired time based on the stored associated classical information tagged to the one qubit of the pair of entangled qubits; g) measuring the one qubit of the pair of entangled qubits stored unloaded; and h) Based on the measurements, generating shared relevant state information, the shared relevant state information being private to an eavesdropper. The method of claim 14 , wherein the desired time is on-demand. The method of claim 14 , wherein the desired time is predetermined.

17. The method of claim 14, wherein the expected time is based on a lifetime of a qubit. The method of claim 14 , wherein the desired time is based on application requirements.

19. The method of claim 18, wherein the application requirement is based on at least one of: an entanglement property of a qubit, a basis of a qubit, a fidelity of a qubit, an arrival time of a qubit, a source of a qubit, an age of a qubit, a half-life of a qubit, a birth time of a qubit, a flight time of a qubit, a type of qubit, or an identity of the other of the two nodes.

20. The method of claim 14, wherein the associated classical information tagged to the one qubit in the pair of entangled qubits comprises an index.

21. A quantum encoding and decoding system, comprising: a) an entanglement server that generates a first entangled qubit at a first output and generates a second entangled qubit at a second output coupled to the quantum channel; b) a first cache coupled to a first output of the entanglement server, the first cache comprising a quantum repository configured to store qubits and a classical repository configured to store classical tag information associated with the stored qubits, the first cache configured to provide the first entangled qubit at the output at a first time based on the classical tag information associated with the first entangled qubit; c) a transmitter having an input coupled to the output of the first quantum cache and an output coupled to the quantum channel, the transmitter configured to modulate the first entangled qubit from the first cache with classical information to produce encoded classical information, and configured to provide the modulated first entangled qubit to the quantum channel; d) a second cache coupled to the quantum channel, the second cache comprising a quantum storage repository configured to store the qubit and a classical storage repository configured to store classical tag information associated with the stored qubit, the second cache being configured to receive the second entangled qubit and to provide the second entangled qubit at an output at a second time based on the classical tag information associated with the second entangled qubit; as well as e) a receiver having an input coupled to the output of the second quantum cache and an input coupled to the quantum channel, the receiver configured to receive the modulated first entangled qubit and to receive the second entangled qubit from the second cache at a second time, and further configured to process the received modulated first entangled qubit and the received second entangled qubit to provide decoded classical information.

22. The quantum encoding and decoding system of claim 21, wherein the first entangled qubit comprises a photon qubit.

23. The quantum encoding and decoding system of claim 21, wherein the first entangled qubit comprises an atomic qubit.

24. The quantum encoding and decoding system of claim 21, wherein the entanglement server is further configured to provide the qubits to the second cache during a quiet interval of the quantum channel.

25. The quantum encoding and decoding system of claim 21, wherein the entanglement server is further configured to provide the qubits to the second cache before the classical information is known.

26. The quantum encoding and decoding system of claim 21, wherein the classical tag information associated with the first entangled qubit and the second entangled qubit comprises at least one of: qubit fidelity, qubit index, qubit age, qubit type, qubit half-life, qubit error rate, or qubit access time information.

27. The quantum encoding and decoding system of claim 21, wherein the classical tag information associated with the first entangled qubit comprises at least one of the following: delay information about a quantum storage repository of the first cache, memory depth information, storage time information, loading delay information, or unloading delay information.

28. The quantum encoding and decoding system according to claim 21, wherein the first transmitter and the entanglement server are located at the same location.

29. The quantum codec system of claim 21, wherein the first transmitter comprises an ultra-dense codec.

30. The quantum encoding and decoding system of claim 21, wherein the quantum storage repository of at least one of the first cache and the second cache is further configured to perform last-in-first-out (LIFO) quantum state ordering.

31. The quantum encoding and decoding system of claim 21, wherein the quantum storage repository of at least one of the first cache and the second cache is further configured to provide random access to at least some of the stored qubits.

32. The quantum encoding and decoding system of claim 21, wherein the receiver is further configured to use stored classical tag information associated with the qubits stored in the second cache to determine which qubit to pull and process with the received modulated first entangled qubit.

33. A quantum cache comprising: a) a quantum storage repository having an input receiving a quantum state having a fundamental quantum property including coherence, the quantum storage repository being configured to store the quantum state and maintain the coherence property of the stored quantum state at a fidelity level; b) a fidelity system having an input coupled to the quantum storage repository, the fidelity system being configured to use monitoring to maintain the coherence property of the quantum state at the fidelity level to identify whether the quantum state has a coherence property that is not at the fidelity level, the fidelity system being further configured to generate classical data about the quantum state if the coherence property is not at the fidelity level, wherein the generated classical data comprises an index associated with the quantum state; as well as c) An output adapted to transmit the generated classical data on the quantum state with the associated index through a classical channel.

34. A quantum cache as claimed in claim 33, wherein the quantum storage repository comprises atomic quantum memory.

35. A quantum cache as claimed in claim 33, wherein the quantum storage reservoir comprises a fibre delay line.

36. The quantum cache of claim 33, wherein the fidelity system identifies quantum states having coherent properties that are not at the fidelity level based on coherence half-life.

37. The quantum cache of claim 33, wherein the fidelity system probabilistically identifies quantum states having coherent properties that are not at the fidelity level.

38. The quantum cache of claim 33, wherein the fidelity system identifies quantum states having coherent properties that are not at the fidelity level in a deterministic manner.

39. The quantum cache of claim 33, wherein the fidelity system identifies quantum states having coherent properties that are not at the fidelity level based on a collection of quantum states.

40. The quantum cache of claim 33, wherein the fidelity system is further configured to remove quantum states from the quantum storage repository that are identified as having coherent properties that are not at the fidelity level.

41. The quantum cache of claim 33, further comprising an application system having an input coupled to the classical channel and a processor for sending and receiving application commands to an application.

42. A quantum cache as claimed in claim 41, wherein the application system comprises a quantum measurement system.

43. The quantum cache of claim 41, wherein the application system comprises a quantum processor system.

44. The quantum cache of claim 41, wherein the application system comprises a quantum logic element.

45. The quantum cache of claim 41, wherein the application system is connected to the second quantum cache.

46. ​​The quantum cache of claim 41, wherein the application system comprises an addressing application.

47. The quantum cache of claim 41, wherein the application comprises providing shared node metadata.

48. The quantum cache of claim 41, wherein the application comprises clock synchronization.

49. The quantum cache of claim 41 further comprising a classical storage repository.

50. The quantum cache of claim 49, wherein the processor sends classical cache management commands to the classical storage repository.

51. A quantum cache according to claim 49, wherein the classical storage repository is configured to store additional classical data indexed to identified quantum states having coherent properties that are not at said fidelity level.

52. The quantum cache of claim 51, wherein the additional classical data comprises at least one of: an entanglement property, a basis for the identified quantum state, a fidelity of the identified quantum state, an identified arrival time of the identified quantum state, a source of the identified quantum state, an age of the identified quantum state, a half-life of the identified quantum state, or a type of the identified quantum state.

53. The quantum cache of claim 49, wherein the processor sends quantum cache management commands to the quantum repository.

54. A quantum cache comprising: a) a quantum storage repository having an input receiving a quantum state having a fundamental quantum property including coherence, the quantum storage repository being configured to store the quantum state and maintain the coherence property of the stored quantum state at a fidelity level; b) a fidelity system having an input coupled to the quantum storage repository, the fidelity system configured to use monitoring to maintain the coherence property of the quantum state at the fidelity level to identify whether the quantum state has a coherence property that is not at the fidelity level, the fidelity system further configured to generate classical data about the quantum state; c) an output adapted to transmit the generated classical data on the quantum state with the associated index through a classical channel; as well as d) An application system having an input coupled to the classical channel, the application system being configured to send and receive application commands to the application.

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