System and method for long distance quantum capability internet

Abstract

A quantum-enabled internet (QEI) including a quantum-enabled networking architecture integrating advanced communication systems with long-range quantum communication hardware and methods of operation thereof. Using a quantum network (QN) design paradigm, there is provided a physically-centric stack-based quantum network paradigm to control the dynamics of multiple optical-matter Hamiltonians across long-range nodes. This QN network facilitates a basic long-range quantum network service - high visibility Hong-Ou-Mandel interference of telecommunication quantum states generated in two independent, telecommunication-compatible quantum light-matter interfaces separated by a distance. The QN paradigm design can be applied to demonstrate scalable long-range QN services in a QN infrastructure, including transmission of polarization entanglement from a high-repetition source of entangled photons and storage of telecommunication polarization entanglement using remotely located quantum memories capable of heralding entanglement storage using non-destructive measurements and quantum state tomography.

Description

[0001] Cross-reference to related applications This application claims priority to provisional application U.S. Serial No. 63 / 615472, filed December 28, 2023, pursuant to 35 USC §119, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0002] This disclosure generally relates to quantum-enabled communication networks, and more specifically, to a quantum-enabled internet employing a combination of software-defined and time-sensitive networking with quantum communication between quantum memories. Background Technology

[0003] Quantum networks comprise nodes capable of creating, processing, and storing quantum information via entangled links for transmission. These networks provide a non-monolithic approach to quantum technology development, allowing for scalable and parallel development of communication, information processing, or metrology solutions.

[0004] The development of quantum networks is still far from its vision of becoming the Internet and is ongoing. Small-scale quantum entanglement and cryptographic networks emerged in the early 21st century and are now flourishing, with quantum network experiments targeting the direct entanglement distribution, quantum state transfer, and interference-mediated entanglement generation between quantum network nodes. Recently, efforts have been made to promote larger-scale quantum communication experiments, aiming to develop quantum repeaters and distributed quantum processing networks. Summary of the Invention

[0005] In some embodiments, rules are constructed for quantum communication in a manner similar to the development of the Transmission Control Protocol / Internet Protocol (TCP / IP) protocol stack for classical computer networks. In some embodiments, the techniques disclosed herein deconstruct the quantum communication process into resource-specific tasks or protocols.

[0006] This disclosure relates to quantum networks, and more specifically, to systems and methods for providing a quantum network framework that includes quantum network operation at the protocol and design levels.

[0007] In one aspect of this disclosure, the design, deployment, and implementation of an example of a QEI network are provided, which connects QM-QFC atomic ensembles over a relatively long distance (e.g., 158 km) of deployed optical fibers. Using a novel QN design paradigm, a stack-driven ubiquitous QN service is demonstrated to deliver long-distance, robust HOM interference with high visibility.

[0008] In some embodiments, a system for performing operations on a quantum network is provided. The system includes quantum manipulation elements configured to directly manipulate and transmit quantum information. The system also includes a central controller configured to synchronize and orchestrate the operation of the quantum manipulation elements toward orchestrated actions, which at least include generating entangled photons, quantum memory operations, and quantum measurements. The system further includes a controllable instrument configured to interface with and drive the quantum manipulation elements, the controllable instrument translating control commands from the central controller into operating parameters for the quantum manipulation elements, and the controllable instrument further configured to provide feedback from the quantum measurements to the central controller.

[0009] In some embodiments, the central controller is a general-purpose computer, a field-programmable gate array, and / or another classic computer processor.

[0010] In some embodiments, the controllable instrument is functionally grouped into subsystems and settings, and also includes a clock interface for distributing timing information to the subsystems and settings.

[0011] In some embodiments, the clock interface further facilitates subsynchronous resolution for coherent manipulation of quantum information.

[0012] In some embodiments, the controllable instrument is also configured to perform compensation between long-distance or long-range connections to maintain coherence between different nodes on relevant time scales.

[0013] In some embodiments, the controllable instrument includes at least a signal generator, a timer, and an oscilloscope.

[0014] In some embodiments, the quantum manipulation element includes at least atoms, optical fibers, optical elements, and photodetectors.

[0015] In some embodiments, the central controller is also configured to manage quantum information, use models learned from data acquired from self-quantum measurements to understand the quantum network, and use the learned understanding to verify the quantum network.

[0016] In some embodiments, the first set of application programming interfaces is used to interface the central controller with a controllable instrument interface, wherein one or more of the first set of application programming interfaces are used to transmit control commands from the central controller.

[0017] In some embodiments, the first set of application programming interfaces operates independently of the brand and model of the controllable instrument.

[0018] In some embodiments, the second set of application programming interfaces is used to interface the central controller with one or more user-defined quantum network application interfaces.

[0019] In some embodiments, user-defined quantum network applications include at least distributed quantum gate operations, teleportation-based services and HOM indistinguishability verification, and entanglement swapping.

[0020] In some embodiments, a method for operating a quantum network is provided. The method includes configuring quantum manipulation elements to directly manipulate and transfer quantum information. The method also includes configuring a central controller to synchronize and orchestrate the operation of the quantum manipulation elements toward orchestrated actions, said orchestrated actions including at least the generation of entangled photons, quantum memory operations, and quantum measurements. The method further includes configuring controllable instruments to interface with and drive the quantum manipulation elements, the controllable instruments translating control commands from the central controller into operating parameters for the quantum manipulation elements, and the controllable instruments are further configured to provide feedback from quantum measurements to the central controller. The quantum network operates via a hierarchy of interfaces between the quantum manipulation elements and the controllable instruments, and between the controllable instruments and the central controller.

[0021] In some embodiments, a method for quantum frequency conversion is generally described. The method may include receiving a first signal encoding a qubit, wherein the first signal has a first frequency. The method may further include receiving at least one laser beam. The method may further include configuring the at least one laser beam to generate at least one control beam. The method may further include combining the first signal with the at least one control beam to generate a second signal encoding the qubit, wherein the second signal has a second frequency at which the second signal is stored in a quantum memory device.

[0022] In some embodiments, at least one laser beam may include a first laser beam having a third frequency and a second laser beam having a fourth frequency. Configuring the at least one laser beam may include configuring the first beam to generate a first control beam and configuring the second beam to generate a second control beam. Combining a first signal with at least one control beam may include combining the first signal with the first and second control beams to generate a second signal.

[0023] In some embodiments, the first frequency may be 780 nanometers (nm), the second frequency may be 1324 nm, the third frequency may be 795 nm, and the fourth frequency may be 1367 nm.

[0024] In some embodiments, configuring a first beam to generate a first control beam may include modulating the first beam. Configuring a second beam to generate a second control beam may include frequency locking of the second beam.

[0025] In some embodiments, an electro-optic modulator (EOM) can be used to attenuate the first signal to create a field envelope of the first signal.

[0026] In some embodiments, frequency locking of the second beam may include operating an indium gallium arsenide (InGaAs) balanced amplified photodetector to obtain an optical-optical dual resonance (OODR) spectrum, scanning the second beam while maintaining the first signal frequency locked, generating an error signal by modulating the second beam at a predetermined frequency, and operating a proportional-integral-derivative (PID) controller to lock the second beam according to the error signal.

[0027] In some embodiments, combining the first signal with at least one control beam may include resonantly coupling a first state of a diamond energy scheme to a third excited state of the diamond energy scheme. The diamond energy scheme may include a first state as the ground state, a second state as an excited state having a higher energy than the first state, a third state as an excited state having a higher energy than the second state, and a fourth state as an excited state having a higher energy than the third state. The input quantum field receiving the first signal can be connected through the first and third states of the diamond energy scheme, and the output quantum field outputting the second signal can be connected through the second and fourth states of the diamond energy scheme. The first state can be coupled to the second state, and the third state can be coupled to the fourth state of the diamond energy scheme.

[0028] In some embodiments, at least one control bundle may be filtered out to obtain a second signal.

[0029] In some embodiments, filtering out at least one control beam may include using a Glan laser (GL) polarizer and at least one wavelength filter.

[0030] In some embodiments, the quantum memory device may be a room temperature vapor cell.

[0031] In some embodiments, a system for quantum frequency conversion is generally described. This system may include a combining optical device and a frequency conversion device. The combining optical device may be configured to generate a first signal encoding a qubit, wherein the first signal has a first frequency. The combining optical device may also be configured to generate at least one laser beam. The combining optical device may further be configured to generate at least one control beam based on the at least one laser beam. The frequency conversion device may be configured to combine the first signal with the at least one control beam to generate a second signal encoding the qubit, wherein the second signal has a second frequency. The frequency conversion device may also be configured to store the second signal in a quantum memory device.

[0032] In some embodiments, the combined optical device may include a first laser pump field configured to generate a first signal and at least one additional laser pump field configured to generate at least one laser beam.

[0033] In some embodiments, at least one laser beam may include a first laser beam having a third frequency and a second laser beam having a fourth frequency. At least one additional laser pump field may include a second laser pump field configured to generate the first laser beam and a third laser pump field configured to generate the second laser beam.

[0034] In some embodiments, the combining optical device may be configured to configure a first beam to generate a first control beam, configure a second beam to generate a second control beam, and the frequency conversion device may be configured to combine a first signal with the first and second control beams to generate a second signal.

[0035] In some embodiments, the first frequency may be 780 nanometers (nm), the second frequency may be 1324 nm, the third frequency may be 795 nm, and the fourth frequency may be 1367 nm.

[0036] In some embodiments, the combined optical device can be configured to generate a first control beam by modulating a first beam, and to generate a second control beam by frequency locking a second beam.

[0037] In some embodiments, the combined optical device may be configured to use an electro-optic modulator (EOM) to attenuate a first signal to create a field envelope of the first signal.

[0038] In some embodiments, in order to frequency lock the second beam, the combined optical device can be configured to operate an indium gallium arsenide (InGaAs) balanced amplified photodetector to obtain an optical-optical dual resonance (OODR) spectrum, scan the second beam while keeping the first signal frequency locked, generate an error signal by modulating the second beam at a predetermined frequency, and operate a proportional-integral-derivative (PID) controller to lock the second beam according to the error signal.

[0039] In some embodiments, to combine the first signal with at least one control beam, the frequency conversion device can be configured to resonantly couple a first state of the diamond level structure to a third excited state of the diamond level structure. The diamond level structure may include a first state as the ground state, a second state as an excited state having a higher energy than the first state, a third higher state as an excited state having a higher energy than the second state, and a fourth state as an excited state having a higher energy than the third state. The input quantum field receiving the first signal can be connected through the first and third states of the diamond level structure, and the output quantum field outputting the second signal can be connected through the second and fourth states of the diamond level structure. The first state can be coupled to the second state, and the third state can be coupled to the fourth state of the diamond level structure.

[0040] In some embodiments, the frequency conversion device may be configured to filter out the at least one control beam to obtain the second signal.

[0041] In some embodiments, the frequency conversion device may include a GL laser polarizer and at least one wavelength filter configured to filter out at least one control beam.

[0042] In some embodiments, the quantum storage device may be a room temperature vapor chamber.

[0043] In some embodiments, a method for determining the indistinguishability between qubits is generally described. The method may include receiving a first packet of photons from a first quantum memory. The method may also include receiving a second packet of photons from a second quantum memory. The method may further include determining a first arrival time of the first packet of photons. The method may further include determining a second arrival time of the second packet of photons. The method may further include determining the difference between the first and second arrival times. The method may further include determining the overlap rate between the first and second packets of photons. The method may further include determining HOM visibility based on the overlap rate and the difference between the first and second arrival times. HOM visibility can indicate the indistinguishability between the first and second packets of photons.

[0044] In some examples, a first packet of photons can be received from a first quantum memory via a first optical path having a first distance, and a second packet of photons can be received from a second quantum memory via a second optical path having a second distance different from the first distance.

[0045] In some examples, the polarization of the first packet of photons and the polarization of the second packet of photons can be compensated.

[0046] In some examples, the difference between the average number of photons in the first packet and the average number of photons in the second packet can be within a predetermined threshold that maximizes HOM visibility.

[0047] In some examples, the average number of photons in the first packet and the average number of photons in the second packet can be defined within a pulse time envelope.

[0048] In some examples, the first and second packets of photons can be received by the HOM detection system. The HOM detection system, the first quantum memory, and the second quantum memory can be located in the same location.

[0049] In some examples, the same location including the first quantum memory, the second quantum memory, and the HOM detection system can be the first location. The first quantum memory can receive a first packet of photons from a first light source located at a second location different from the first location. The second quantum memory can receive a second packet of photons from a second light source located at a third location different from both the first and second locations.

[0050] In some examples, multiple optical elements can be used to compensate for the polarization of the first and second packets of photons to guide macroscopic light to a polarimeter for measurement. Multiple optical elements can be automatically removed to release the first and second packets of photons into the HOM detection system.

[0051] In some examples, determining the overlap rate may include determining that a first arrival time is within a time period, determining that a second arrival time is within a time period, and recording the overlap count in response to determining that the first and second arrival times are within a time period.

[0052] In some examples, the first time of arrival can be a photon detection event in the first set of photon detection events in the first channel of the first packet of received photons. The second time of arrival is a photon detection event in the second set of photon detection events in the second channel of the second packet of received photons. The overlap count can be within the number of overlap counts.

[0053] In some examples, the number of coincidence counts can be the number of first coincidence counts. A delay can be added to at least one of the first and second channels. Using the added delay, a first set of photon detection events can be monitored in the first channel, and a second set of photon detection events can be monitored in the second channel. A second number of coincidence counts can be determined based on the monitoring with the added delay. A relationship between the first number of coincidence counts and the second number of coincidence counts can be determined.

[0054] In some examples, the delay can be adjusted to minimize the overlap rate based on the relationship between the first and second overlap counts, where minimizing the overlap rate maximizes HOM visibility and indistinguishability. Attached Figure Description

[0055] Figure 1 A quantum network including a nonlocal Hamiltonian is conceptually described, which allows for hierarchical operation with a basic process defined as primitives (time modulation of Hamiltonian parameters) for establishing a network protocol that produces services as a result, according to embodiments herein. Figure 2The optical infrastructure between two nodes according to embodiments of this document is generally described, which uses four optical fibers (e.g., 70 km) to transmit quantum information and for time synchronization and classical data signals; Figure 3 A quantum enabling (QE) architecture is described, which abstracts the implementation of QE processes orchestrated by the control plane and executed at the quantum enabling interface plane, where control drips down to the quantum data plane, thereby causing the forwarding of quantum information; Figure 4A A QM-QFC setup for achieving frequency locking of a 1367 nm laser and creation of the field envelope of a 780 nm signal using an optical-optical dual resonance (OODR) laser stabilization setup according to an embodiment is described. Figure 4B A flowchart of an example QM-QFC process according to an embodiment is depicted; Figure 5A It is a graph depicting example input and output pulses detected by the SNSPD used to estimate the efficiency of the QFC process in the embodiment; Figure 5B This is an example measurement of the photon number (diamond) and signal-to-noise ratio (SNR) (triangle) at the detector for a QFC pulse at 1324 nm, which is a function of the average photon number in the 780 nm input pulse at the Alice and Bob nodes. Figures 6A-6B This is a schematic diagram depicting the physical network nodes forming a QEI according to embodiments herein; Figure 6C A flowchart depicts an example process that can be performed by a measurement node according to an embodiment; Figure 7A It is a graph depicting a histogram of jitter events in a 70 km shared clock network, wherein in an embodiment, a node (e.g., referred to as Charlie) is the master clock in a tree configuration connecting two nodes (e.g., referred to as Alice and Bob); Figure 7B It is a graph depicting the histogram of jitter events in the full 70 km QN link between the two nodes after several hours of integration time in the embodiment. Figure 7C The distribution of polarization states between two nodes is depicted, with compensation performed every 15 minutes within a 12-hour integration period, including an upper plot showing close-ups of stable time periods (e.g., around midnight) and time periods with more fluctuations (e.g., early morning). Figure 7D The distribution of time required to stabilize the transmitted PS to the desired state is depicted. The illustration shows that no correlation with time of day was observed during the observation period; Figure 7E The graphs depict the free drift time of maintaining polarization fidelity after compensation is performed, according to the example embodiment (top) and the graphs depict the polarization fidelity measurement of the feedback being activated every predetermined number of minutes during the collection time in hours (bottom). Figures 8A-8B An exemplary implementation of the QE interface plane is depicted: a QEI testbed between two nodes has two identical co-located nodes at one site and a third node at the second site; and the quantum optics system setup in the embodiment and the devices of each node in the quantum optics subsystem, which are functionally encoded, their connectivity, and their grouping are shown. Figures 9A-9B The HOM protocol and network primitives executed by the active QEIP component in the embodiments are described; Figures 10A-10B An overview of a stack-driven quantum memory (QN) is depicted, comprising three optical network layers (e.g., a classical control network layer for user-defined control and fast feedback); a quantum-enabled network layer supporting time, phase, and polarization simulation measurements; and quantum network layers including room-temperature quantum memories, qubit detection systems, and photonic quantum signal transmission according to embodiments. Figure 11A The arrangement sequences used for QM QFC generation and long-range HOM interference in the embodiments are described; Figure 11B A 1324FWM HOM pulsed quantum interference experiment operating at the node for a 20km QEI configuration is depicted, with the continuous wave HOM shown in the inset. Figure 11C-11E A graph depicts 1324 FWM HOM pulse quantum interference experiments operating at an example location for a long-distance QEI configuration in one embodiment, wherein measurements were taken for different average photon numbers at the inverter outlet; and Figure 12 This is a flowchart illustrating a method for operating a quantum network in some embodiments. Detailed Implementation

[0056] This disclosure will now be described in more detail with reference to the following discussion and the accompanying drawings. In the following description, numerous specific details, such as particular structures, components, materials, dimensions, processing steps, and techniques, are set forth in order to provide an understanding of various embodiments of this disclosure. However, those skilled in the art will appreciate that various embodiments of this disclosure can be practiced without these specific details. As used throughout this disclosure, the term “about” generally means no more than ±10%, ±5%, ±2%, ±1%, or ±0.5% of a certain number. When a range is expressed in this disclosure as a range from one number to another (e.g., 20 to 40), this disclosure contemplates any value within that range (i.e., 22, 24, 26, 28.5, 31, 33.5, 35, 37.7, 39, or 40) or any quantity defined by either of two values ​​that may exist within that range (e.g., 28.5-35).

[0057] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that, when used in this disclosure, the terms “comprising” and / or “including” specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0058] This disclosure relates to a novel, physics-centric stack of quantum networks (QNs) utilizing state-of-the-art classical and quantum communication systems. A method is implemented that follows contemporary network principles while considering the unique system and physical requirements of an internet capable of performing quantum operations across a set of network Hamiltonians: a quantum-enabled internet (QEI). Fiber-optic networks are used to construct high-repetition-rate, long-distance QNs, providing a versatile platform that collaborates with established telecommunications infrastructure and improves cost-effectiveness. Furthermore, time-evolutionary optical-matter interconnects based on atomic systems with energy transitions at telecommunication wavelengths are realized, facilitating efficient quantum information transfer across QN nodes. This disclosure further demonstrates a concept for a quantum-enabled architecture that integrates advanced communication management principles with high-fidelity QN services. In some embodiments, long-distance quantum network services can be provided, for example, using Hung-Ow-Mandel interference of telecommunication photons generated in independent quantum memories spaced far apart (e.g., 158 km).

[0059] like Figure 1As shown, in some embodiments, to construct instances of QEI based on long-distance measurements, the QN paradigm employs an operational level 10 corresponding to the operational levels of classical networks. This abstraction views QN as a set of dynamic Hamiltonians 12 located at QN nodes, and the QN protocol as a QN process obtained by simultaneously driving and measuring the set of remotely located Hamiltonians 12. The complex process of large QN is decomposed into QN primitives 15, which perform time manipulation of Hamiltonian parameters for QN node operations. These primitives are grouped into QN protocols 20, which guide the evolution of the entire network. Results derived from quantum observables associated with the basic QN protocol (e.g., long-distance HOM interference or entanglement distribution and swapping) are defined as QN services 25.

[0060] In some embodiments, to implement quantum protocols and develop quantum communication services and standards, a quantum enabling (QE) protocol stack 30 is designed, which includes deterministic QE protocols required for preparing, controlling, and monitoring quantum network operation at each step of the communication process. This QE protocol stack 30 is a hierarchy defining the following: a QE application layer; a QE transport layer; a QE network routing layer; a QE link layer; and a QE physical layer. The QE protocols are responsible for the physical implementation of QN primitives and protocols. This establishes guidelines for using auxiliary classical networks to support QN services and develop a quantum internet stack 40. The quantum internet stack 40 is a hierarchy defining the following: a distributed quantum processing layer; a protocol layer based on quantum teleportation; a quantum network entanglement routing layer; a quantum link: entanglement transfer layer; and a quantum physical layer.

[0061] More specifically, see reference Figure 1 A quantum network (QN) comprises nonlocal Hamiltonians 12 that allow hierarchical operation, where fundamental processes are defined as primitives. These primitives perform time modulation of Hamiltonian parameters—establishing network protocols that produce services as results. These protocols can be organized into a quantum protocol stack 40 for quantum communication networks. This concept is implemented using auxiliary structures to achieve robust construction of quantum primitives and protocols. These quantum-enabled processes can be grouped into supporting protocol stack 30. The basic quantum-enabled protocols involve preparing and controlling physical parameters corresponding to Hamiltonian parameters and distributing a global sense of time throughout the network.

[0062] like Figure 2As shown, this disclosure also provides a quantum-enabled network architecture 50 for employing a combination of software-defined and time-sensitive networking with quantum memories for quantum communication, including providing basic long-distance quantum network services using HOM (Honoré-Mandel) interference of telegraph photons generated in two independent quantum memories separated by a distance. In a non-limiting illustrative example, the two QN nodes 60, 70, each with a corresponding independent quantum memory, are separated by a distance of, for example, 158 km (non-limiting). Figure 2 In the illustrated embodiment, the quantum-enabled network architecture 50 includes two QE nodes 60 and 70, which are spaced apart and connected via fiber optic infrastructure 75 (e.g., using four 70 km commercial single-mode fibers). One pair of fibers 76 is used for quantum information, and another pair of fibers 78 is used for time synchronization and classical data signals. The quantum nodes Alice, Bob, and Dave are located together at a node (e.g., node 60, also referred to as the first node or first site associated with the network entity at a first location), where the Charlie node is located at node 70 (also referred to as the second node or second site associated with the network entity at a second location). The additional fiber optic loops at nodes 60 and 70 allow for phase independence in the quantum channel.

[0063] In this embodiment, the Quantum Enabled Internet (QEI) operates according to a network management strategy characterized by the separation of control and forwarding operations for the quantum hardware. This separation and centralized control allows for the manipulation of non-local operations involving entanglement. The quantum hardware or device is the forwarding element and will be part of the forwarding plane; however, manipulation of quantum information from the control plane is hierarchical.

[0064] The medium of qubits in a network is a photon. Manipulation of photonic qubits (or optical qubits) is achieved through absorption and emission systems with energy levels (e.g., atoms, ions). Manipulation of these systems is achieved through electromagnetic fields, driven by controllable instruments such as signal generators. Therefore, a controllable quantum device comprises a system capable of manipulating qubits and associated control elements. However, separating the control elements from the qubit manipulation (forwarding) elements to distinguish between control operations and the resulting quantum phenomena / behaviors is useful. This is useful because it provides the flexibility to modify the control elements while maintaining quantum gauge. This separation also acknowledges that qubit manipulation is performed via an intermediary or interface. This results in the forwarding plane splitting into a quantum enable interface plane and a quantum data plane.

[0065] According to the embodiments described herein, Figure 3A quantum-enabled network architecture 100 is depicted, in which the execution of QE protocols and the operation of the quantum-enabled internet (QEI) occur, as understood through an architectural model. The QEI architecture 100 comprises four coexisting planes: the Quantum Application Plane (QAP) 110, the Control Plane (CP) 120, the Quantum Enabled Interface Plane (QEIP) 130, and the Quantum Data Plane (QDP) 140. The QEI architecture 100 abstracts the implementation of the QE processes orchestrated by the Control Plane (CP) 120 and executed at the Quantum Enabled Interface Plane (QEIP) 130. Therefore, control drips down to the Quantum Data Plane (QDP) 140, resulting in the forwarding of quantum information. Control commands and measurements are exchanged between the planes via a quantum-enabled application programming interface.

[0066] QDP 140 is responsible for manipulating and transferring quantum information. When timing control signal 122 and driver control signal 125 from CP 120 drip down through QEIP 130, QDP 140 enables the qubit manipulation medium to be directed toward operations such as generating entangled photons, quantum memory operations, and quantum measurements. QN primitives and protocols are implemented in QDP. As a non-limiting example, QDP 140 includes quantum manipulation elements or components, such as, but not limited to, atoms, optical fibers, optical elements, and photodetectors, configured to directly manipulate and transfer quantum information.

[0067] In some embodiments, QEIP 130 of QN operation includes all control and interface elements for forming multiple systems of QN 100. The control and interface elements are grouped by device organization functionality or type into subsystem configuration 142 and setup configuration 145. In some embodiments, setup configuration 145 includes the configuration of devices (e.g., actuator and / or probe drivers) that obtain direct command sequences from their node controllers for operation. The devices (e.g., actuator and / or probe drivers) of subsystem configuration 142 are operated via an intermediate controller (e.g., a computer / Field Programmable Gate Array (FPGA)) that manages the control software and / or drivers. At the individual node level, the node controller is an entity that orchestrates the operation of all node components either by directly orchestrating the set of devices or by interfaceing with the subsystem controller to perform operations. Elements within setup configuration 145 are managed by a central network controller 150. Within subsystem configuration 142, the central network controller 150 delegates control to task-specific controllers. Additionally, to maintain time consistency across the entire network, QEIP 130 includes or uses a precision clock system 160 that provides a clock interface to distribute timing information to setup 145 and subsystem 142. In an embodiment, QEIP 130 utilizes a White Rabbit (WR) network to establish a network clock whose time jitter is shorter than the duration of photons propagating through the QN. As a non-limiting example, QEIP 130 includes a controllable instrument configured to interface with and drive a quantum manipulation element. The controllable instrument translates control commands from a central controller into operating parameters for the quantum manipulation element. The controllable instrument is also configured to provide feedback from quantum measurements to the central controller. Examples of controllable instruments include, but are not limited to, signal generators, time stamps, and oscilloscopes.

[0068] CP 120 is centralized and responsible for managing and forwarding quantum information via QEIP 130. The southbound quantum enabling (QE) application programming interface (API) 133 enables communication from CP 120 to QEIP 130, allowing operations based on nonlocal entanglement. The southbound quantum enabling (QE) API 133 is also referred to as the first set of application programming interfaces (APIs). For example, the first set of APIs is used to interface the central controller with controllable instruments, where control commands from the central controller communicate using one or more of the first set of APIs. The northbound QE-API 136 allows user or higher-level functions to interface with the central controller 160 and obtain a network-wide view of available capabilities. The northbound QE-API 136 is also referred to as the second set of APIs. The second set of APIs can be used to interface the central controller with one or more user-defined quantum network application interfaces. User-defined quantum network applications include at least distributed quantum gate operations, teleportation-based services, HOM indistinguishability verification, and entanglement swapping. The southbound quantum enablement (QE) application programming interface (API) 133 refers to the API that interfaces with operations at the QEIP 130 level (e.g., with the quantum subsystem (also referred to as subsystem configuration 142) and the quantum setup (which interfaces directly with the device using a driver). The quantum setup is also referred to as setup configuration 145. The northbound QE-API 136 refers to the API that interfaces with operations at the quantum application plane 110 level. In some embodiments, the control plane (CP) 120 controls and makes decisions. The CP 120 understands the underlying quantum system, how the controller is directly responsible for the quantum system, and the overall network operation. The CP 120 uses models learned from data obtained from measurements to develop an understanding of the system (e.g., distribution learning / parameter estimation using stochastic variational inference or conformal prediction) and uses them to inform device and network control and verification. The CP 120 includes a central controller configured to synchronize and orchestrate the operations of quantum manipulation elements toward orchestrated actions. Examples of orchestrated actions include, but are not limited to, generating entangled photons, quantum storage operations, and quantum measurements.

[0069] Application Programming Interface Supporting Quantum More specifically, given Figure 3The Quantum Enablement (QE) Application Programming Interfaces (APIs) 133 and 136 define how the control plane 120 communicates with the QE interface plane 130 and the quantum application plane 110. The southbound QE-API 133 includes drivers that handle communication between the controller 150 and all device and subsystem controllers 135 on the QE interface plane 130. In some embodiments, these drivers are written in Python and are based on the Virtual Instrument Software Architecture (VISA) protocol and custom device communication standards. Depending on their functionality, these libraries follow a design pattern to uniformly control networked devices. As an example, Figures 9A-9B The document illustrates the eight QE protocol steps constructed from these drivers.

[0070] The Northbound QE-API 136 is, for example, a Python command written on top of the eight-protocol process. They can extract measurement and state information along all procedural steps, including average photon number, temporal photon shape, and HOM visibility. A dashboard / GUI has been developed to present relevant information when executing the QN protocol using the Northbound QE-API.

[0071] QAP 110 provides a facade for all network operations, allowing them to be addressed independently of lower-level operations. QAP 110 includes higher-level entanglement-based applications 112, such as distributed quantum gate operations and teleportation-based services, as well as lower-level QN services 115, such as HOM indistinguishability verification or entanglement swapping. This enables the development of user-defined network operations and more complex quantum network operations.

[0072] Therefore, while including all implementation details, focusing on different planes provides different and useful perspectives on network operation. QDP 140 is measurement-oriented and describes fundamental quantum operations. QEIP 130 describes the operation of the control hardware used for implementation. CP 120 describes the understanding of the system based on the mathematical model and the control variables associated with QEIP 130. QAP 110 provides a high-level understanding of the operation.

[0073] In some embodiments, as described in further detail above and below, a method for operating a quantum network is provided. Figure 12 This is a flowchart illustrating a method or operation of a quantum network in some embodiments. At 1202, the method includes configuring quantum manipulation elements to directly manipulate and transmit quantum information. In some embodiments, the quantum manipulation elements include at least atoms, optical fibers, optical elements, and photodetectors.

[0074] At 1204, the method further includes configuring a central controller to synchronize and orchestrate the operations of the quantum manipulation elements toward orchestrated actions. In some embodiments, orchestrated actions include at least generating entangled photons, quantum storage operations, and quantum measurements.

[0075] At 1206, the method further includes configuring a controllable instrument to interface with and drive the quantum manipulation element. In some embodiments, the controllable instrument translates control commands from a central controller into operating parameters for the quantum manipulation element. In some embodiments, the controllable instrument is also configured to provide feedback from quantum measurements to the central controller.

[0076] In some embodiments, the quantum network operates via a hierarchy that interfaces quantum manipulation elements with controllable instruments and interfaces the controllable instruments with a central controller (e.g., interfaces on different planes as described herein). In some embodiments, the controllable instruments are functionally grouped into subsystems and settings, and also include a clock interface for distributing timing information to the subsystems and settings. In some embodiments, the clock interface further facilitates subsynchronous resolution for coherent manipulation of the quantum information. In some embodiments, the controllable instruments are also configured to perform compensation between distance (e.g., long-distance) connections to maintain coherence between different nodes on relevant timescales. In some embodiments, the controllable instruments include at least a signal generator, a time stamp, and an oscilloscope. In some embodiments, the central controller is also configured to manage the quantum information, understand the quantum network using models learned from data acquired from quantum measurements, and verify the quantum network using the learned understanding. In some embodiments, the central controller includes one or more classical computers or computer processors.

[0077] In some embodiments, the method further includes using or configuring a first set of application programming interfaces (APIs) to interface the central controller with a controllable instrument, wherein one or more of the first set of APIs are used to transmit control commands from the central controller. In some embodiments, the first set of APIs operates independently of the brand and model of the controllable instrument. In some embodiments, the method further includes using or configuring a second set of APIs to interface the central controller with one or more user-defined quantum network application interfaces. In some embodiments, the user-defined quantum network applications include at least distributed quantum gate operations, teleportation-based services and HOM indistinguishability verification, and entanglement swapping.

[0078] In addition to utilizing telecommunications fiber optic infrastructure 75 to support entangled distributions and quantum teleportation over extended distances, Figure 2 The quantum-enabled network architecture 50 facilitates the execution of the aforementioned basic quantum services and protocols. What is now described is the use of... Figure 3An embodiment of the implementation of a QEI service in a QEI network architecture 100, which uses long-distance high-visibility HOM interference of telecommunication photonic qubits generated in two independent optical matter systems (at correspondingly separate first and second sites) at nodes 60 and 70 connected by a long-distance (e.g., 158 km) optical fiber.

[0079] Quantum data plane implementation for Figure 3 The QDP 140 implementation selects quantum systems capable of high-fidelity generation and transmission of telecommunications-compatible quantum states, including (i) field-deployable quantum memory-compatible quantum frequency converters (QM-QFCs) operating at telecommunication wavelengths and (ii) HOM interferometer stations for evaluating interoperability between QM-QFCs and quantum interference visibility of qubits after long-distance transmission. These systems are distributed between nodes 60, 70 at separate first and second locations.

[0080] Light-matter quantum interface: quantum-memory compatible quantum frequency converter In the quantum memory-compatible quantum frequency converter (QM-QFC) described in this disclosure, a 780 nm laser input signal is converted into a 1324 nm signal via four-wave mixing (FWM) with two pump fields at 795 nm and 1367 nm. Figure 4A An embodiment of an example apparatus for implementing the QM-QFC described in this disclosure is shown. A 780 nm signal is combined with a 795 nm pump in a polarization beamsplitter, and then combined with a 1367 nm pump beam through a long-pass filter. A half-wave plate (HWP) and a quarter-wave plate (QWP) are used before the GL laser polarizer (GL) to compensate for birefringence. An InGaAs photodetector is used to detect the generated 1324 nm field. An optical-optical double resonance (OODR) laser stabilization setup is used to lock the 1367 nm laser. After the chamber, the pump beam is filtered out by the GL polarizer and a wavelength filter. Figure 4A As shown, the fourth-order diamond atom scheme 235 is used for frequency conversion.

[0081] In one embodiment, the frequency locking of the 1367 nm laser utilizes a wavelength of 780 nm. Leap and at 1367 nm Leap 780 nm optical pump Level, and locked to it using saturated absorption spectroscopy (SAS). Transition. For OODR, the 1367 nm laser is maintained at 60 ℃A 780 nm laser beam propagates in the backpropagation direction within a 7 cm rubidium cell. An InGaAs balanced amplified photodetector obtains the OODR spectrum while scanning the 1367 nm laser, simultaneously locking onto the 780 nm laser. An error signal is generated by modulating the 1367 nm laser at 100 kHz, and a PI controller locks onto the laser based on this error signal.

[0082] The input 780 nm weakly coherent state simulates the readout qubit from the quantum memory. Input field resonant coupled ground state. to excited state 795 nm pump I coupled ground state to excited state And 1367nm pump II coupling To higher excited states The conversion system is governed by a four-wave mixer (FWM) Hamiltonian according to equation (1), as follows: (1) Where N is the number of atoms in the ensemble. It is the generator operator for the input probe field. It is the QFC output field connection state and The generating operator, and These are the pully frequencies of the two pump fields. and It is the dipole coupling strength between the input and output quantum fields. It is the fourth atomic operator of the four-dimensional atomic operator. Each element. This is single-photon detuning. Using an input-output model, it can be shown that the frequency conversion from a 780 nm input field to a 1324 nm output field follows a linear relationship. ,in It is a constant conversion efficiency independent of the average input photon number (see SM for the complete derivation). Both types of rubidium vapor cells contain abundant natural resources. and And it is magnetically shielded. For each QFC, the system Modifications to the parameter set constitute QN primitives. The details of the devices and architectures for implementing QM-QFC are described below.

[0083] refer to Figure 4AThe example system 200 for quantum frequency conversion described in this disclosure. In one embodiment, a node (e.g., node 60) may include two identical systems 200. System 200 may implement a quantum memory-quantum frequency converter (QM-QFC) that converts a first signal having a first frequency into a second signal having a second frequency. The first signal may be a photonic packet encoding a set of qubits comprising at least one qubit, and the second signal may be a photonic packet encoding the same set of qubits as the first signal. Figure 4A As shown, system 200 may include a combined optical device 230 and a frequency conversion device 240. The combined optical device 230 may be a configuration including at least a laser diode (LD) 201, LD 202, LD 203, an electro-optic modulator (EOM) 204, a variable optical attenuator (VOA) 205, an acousto-optic modulator (AOM) 206, a balanced photodetector (BPD) 207, an optical element 208, a beam splitter (BS) 209, at least one optical coupler 210a, 211a, 212a, a long-pass (LP) filter 213, at least one saturated absorption spectrum (SAS) 214, 215, a proportional-integral-derivative (PID) controller 216, a quantum memory 217, and at least one polarization beam splitter (PBS) 218, 219.

[0084] SAS 214 and LD 201 can form a laser pump field configured to output laser light as a signal with a frequency of 780 nanometers (nm). SAS 214 can be an Rb SAS used in conjunction with LD 201 for frequency stabilization. PBS 218 can be configured to split the 780 nm signal output from LD 201 into two orthogonally polarized components—a transmitted beam and a reflected beam. The transmitted beam can be provided to EOM 204, and the reflected beam can be provided to LP filter 213. EOM 204 can be configured to create a field envelope of the 780 nm signal (or the transmitted beam received from PBS 218), and VOA 205 can be configured to attenuate the 780 nm signal within the created envelope. The attenuated 780 nm signal can be output as a first signal 220 from combined optics 230 via optical coupler 211a.

[0085] SAS 215 and LD 202 can form a laser pump field configured to output a laser signal with a frequency of 795 nm. SAS 215 can be an Rb SAS used in conjunction with LD 202 for frequency stabilization. AOM 206 can be configured to modulate the 795 nm signal output by LD 202. The modulated 795 nm signal can be output from combined optics 230 as a first control beam 221 via optical coupler 212a.

[0086] LD 203 can be a laser pump field configured to output laser light as a signal with a frequency of 1367 nm. PBS 219 can be configured to split the 1367 nm signal output from LD 203 into two orthogonally polarized components—a transmitted beam and a reflected beam. The transmitted beam can be provided to optical coupler 210a, and the reflected beam can be provided to BS 209. BS 209 can be configured to split the reflected beam into two beams—a first beam provided to quantum memory 217 and a second beam provided to optical element 208. Optical element 208 can be, for example, a mirror or optical switch configured to modulate the second beam. In one embodiment, optical element 208 can modulate the second beam at 100 kHz. Optical element 208 can route the modulated second beam to quantum memory 217. In one embodiment, quantum memory 217 can be a 7 cm Rb chamber maintained at 60°C. Quantum memory 217 can provide both the first beam and the modulated second beam to LP filter 213.

[0087] The first beam, the modulated second beam, and the reflected beam of the 780 nm signal from PBS 218 can be routed to BPD 207 by LP filter 213. BPD 207 can receive the beam combination from LP filter 213 and obtain the optical-optical double resonance (OODR) spectrum of the 1367 nm signal by scanning the 1367 nm signal, while maintaining phase or frequency lock on the 780 nm signal. In one embodiment, BPD 207 is an indium gallium arsenide (InGaAs) balanced amplified photodetector. The OODR spectrum obtained by BPD 207 can indicate the error between the 1367 nm and 780 nm signals, and this error can be output as an error signal to PID controller 216. PID controller 216 can perform phase or frequency lock on the 1367 nm signal based on the error signal. This error and lock-in loop can be executed to ensure that the 1367 nm signal output by combined optics device 230 is phase or frequency locked with the 780 nm signal. The locked 1367nm signal can be output from the combined optical device 230 as a second control beam 222 via optical coupler 210a.

[0088] Frequency conversion device 240 may be a configuration including at least one optical coupler 210b, 211b, 212b, 232, at least one half-wave plate (HWP) 223a, 223b, 223c, at least one LP filter 224, 229, PBS 225 (which may also be used as a combiner), quantum memory 226, quarter-wave plate (QWP), GL laser (GL) polarizer 228, and bandpass (BP) filter 231. Optical couplers 210b, 211b, 212b may receive a second control beam 222, a first signal 220, and a first control beam 221 from optical couplers 210a, 211a, 212a, respectively. HWP 223a may be an optical device configured to control the polarization of the second control beam 222 by introducing a half-wavelength phase difference. HWP 223b may be an optical device configured to control the polarization of the first signal 220 by introducing a half-wavelength phase difference. HWP223c can be an optical device configured to control the polarization of the first control beam 221 by introducing a phase difference of half a wavelength.

[0089] PBS 225 can combine or merge the first signal 220 with the first control beam 221 from HWP 223b, 223c. LP filter 224 can be configured to pass the second control beam 222 from HWP 223a to quantum memory 226 and route the merged signal from PBS 225 to quantum memory 226. The second control beam 222, along with the merged first control beam 221 and the first signal 220, can be combined at quantum memory 226. Quantum memory 226 can be a room-temperature Rb vapor chamber. The combination at quantum memory 226 can result in the storage of a second signal in quantum memory 226, wherein the second signal has a frequency of 1324 nm, and 1324 nm can be a telecommunications-compatible frequency.

[0090] QWP 227 can be located between quantum memory 226 and GL polarizer 228 to compensate for birefringence. In some embodiments, an additional HWP accompanying QWP 227 can be located between quantum memory 226 and GL polarizer 228. GL polarizer 228, LP filter 229, and BP filter 231 can work together to filter out the first control beam 221 and the second control beam 222 to obtain a second signal 233 with a frequency of 1324 nm, but encoding the same qubits as the qubits encoded by the first signal 220 (or the 780 nm signal). Optical coupler 232 can output the second signal 233.

[0091] Figure 4BA flowchart of an example QM-QFC process 280 according to an embodiment is depicted. Process 280 may include one or more operations, actions, or functions as shown in one or more of blocks S2, S4, S6, S8, S10, and / or S12. Although shown as discrete blocks, depending on the desired implementation, the various blocks may be divided into additional blocks, combined into fewer blocks, eliminated, executed in a different order, or executed in parallel.

[0092] Process 280 may begin at block S2 and / or block S4. At block S2, the QM-QFC system may receive a signal photonically encoded to the qubits, such as a first signal encoding the qubits, and the first signal having a first frequency. At block S2, the QM-QFC system may receive a pump laser beam, such as at least one laser beam. Process 280 may proceed from block S4 to block S6. At block S6, the QM-QFC system may prepare the pump laser beam, such as by adjusting polarization and spatial mode, such as by configuring at least one laser beam to generate at least one control beam. In one embodiment, the at least one laser beam includes a first laser beam having a third frequency and a second laser beam having a fourth frequency. The QM-QFC system may configure the at least one laser beam by configuring the first beam to generate a first control beam and configuring the second beam to generate a second control beam. The QM-QFC system may combine the first signal with the at least one control beam, including combining the first signal with the first and second control beams to generate a second signal. In one embodiment, the first frequency is 780 nanometers (nm), the second frequency is 1324 nm, the third frequency is 795 nm, and the fourth frequency is 1367 nm.

[0093] In one embodiment, a QM-QFC system may configure a first beam to generate a first control beam by modulating the first beam, and configure a second beam to generate a second control beam by frequency locking the second beam. In one embodiment, a QM-QFC system may attenuate a first signal to generate a field envelope of a first laser beam by using an electro-optic modulator (EOM). In one embodiment, frequency locking the second beam may include operating an indium gallium arsenide (InGaAs) balanced amplified photodetector to obtain an optical-optical dual resonance (OODR) spectrum, scanning the second beam while keeping the first signal frequency locked, generating an error signal by modulating the second beam at a predetermined frequency, and operating a proportional-integral-derivative (PID) controller to lock the second beam according to the error signal.

[0094] Process 280 can proceed from boxes S2 and S6 to box S8. At box S8, the QM-QFC system can combine the signal photon at box S2 with the pump laser beam prepared at box S6, for example, by combining the first signal with at least one control beam. In one embodiment, the QM-QFC system can combine the first signal with at least one control beam by resonantly coupling a first state of the diamond level structure to a third excited state of the diamond level structure. The diamond level structure may include a first state as the ground state, a second state as an excited state having a higher energy than the first state, a third higher state as an excited state having a higher energy than the second state, and a fourth state as an excited state having a higher energy than the third state, wherein the input quantum field receiving the first signal is connected through the first and third states of the diamond level structure, and the output quantum field outputting the second signal is connected through the second and fourth states of the diamond level structure, coupling the first state to the second state and coupling the third state to the fourth state of the diamond level structure.

[0095] Process 280 can proceed from block S8 to block S10. At block S10, the QM-QFC system can send the combined beams into a room-temperature vapor chamber for conversion, such as sending the combined first signal along with at least one control beam into a quantum storage device for storage. In one embodiment, the quantum storage device can be a room-temperature vapor chamber. Process 280 can proceed from block S10 to block S12. At block S10, the QM-QFC system can filter out the control beams and the original signal photons from the output to generate a second signal encoding the qubits, wherein the second signal has a second frequency. In one embodiment, the QM-QFC system can use a GL laser (GL) polarizer and at least one wavelength filter to filter out at least one control beam.

[0096] Figure 5A The input and output pulses detected by a superconducting nanowire single-photon detector (SNSPD) used to estimate the efficiency of the QFC process are depicted. and During the cycle time. Evaluate the photon number within the interval, and based on and Evaluate the photon rate in the background noise. Figure 5B The graph depicts the photon count (diamond) of the QFC pulse at 1324 nm as a function of the average photon count in the 780 nm input pulse for Alice 248 and Bob 250, and the signal-to-noise ratio (SNR) at the detector (triangle). The solid and dashed lines represent linear fits to the conversion efficiency and SNR curves, respectively. The calculation was performed using a 100 kHz pulse repetition rate... Data is generated by averaging the results over a 20-minute query period. The error bar is dominated by detection and conversion efficiency errors.

[0097] The FWM QFC process can be driven at efficiencies exceeding 50%. In this embodiment, a trade-off is achieved by reducing QFC efficiency and realizing an operating point with a good signal-to-noise ratio (SNR), the center quality factor in the HOM interference experiment. To measure the conversion efficiency, [the following is used]. For FWHM pulsed currents, Alice's pump I operated at 5.20 mW and pump II at 2.95 mW, while Bob's pump I was set to 0.45 mW and pump II to 2.20 mW. The input pulses were detected using a superconducting nanowire single-photon detector (SNSPD), and the average photon number of the probe and the FWM QFC conversion field could be estimated using the resulting histogram, such as... Figure 5A As shown in the figure, the 780 nm histogram is labeled 246, and the 1324 nm histogram is labeled 245. The conversion efficiency and signal-to-noise ratio were then characterized for different input photon energy levels. The conversion efficiencies of the two QM-QFCs (Alice and Bob) were measured as follows: and ,like Figure 5B As shown in the image.

[0098] Measurement: Hong-O-Mandel interference station At the Charlie station (e.g., the second location) in node 70 and the Dave station (e.g., the first location) in node 60, active feedback compensates for polarization drift caused by propagation in the fiber. A 1324 nm pulse train... and In a 50:50 non-polarizing beam splitter Interference at the point. Beam splitter output measured at the SNSPD. and And calculate the overlap rate between the two interferometer arms.

[0099] Support for quantum interface plane implementation Return to reference Figure 3 QEIP 130 provides functionality for implementing the QN protocol using deployed fiber optic infrastructure. Given... Figure 6A and Figure 6B The QEIP 300 embodiment includes five key physical setups and subsystems: the Alice qubit generation setup at Alice node 310 and the Bob qubit generation setup at Bob node 320, a laser control subsystem 330, a polarization compensation subsystem 340, and a measurement subsystem 350. These systems are configured to provide the time variation of the FWM Hamiltonian, which is used to evaluate the HOM visibility of interference at the end of the quantum channel qubit.

[0100] This paper describes a network clock infrastructure and polarization compensation subsystem capable of sub-nanosecond synchronization resolution, which provides a scalable approach to enabling long-distance single-mode fiber to be compatible with QN operation.

[0101] Figures 6A-6B The physical network nodes forming the QEI are depicted. At a node (e.g., node 60), there are two qubit generation setups: a laser and a measurement subsystem. At another node 70, a polarization compensation and measurement subsystem is hosted. The Alice and Bob qubit generation setups, nodes 310 and 320, share a control and timing infrastructure 360, including a shared network and timing switch 362, a node controller 361, an orchestrator 364, and a multi-channel arbitrary delay generator 366. A laser subsystem 330, including a controller 335 and 795 nm, 780 nm, and 1367 nm lasers, distributes the laser to the Alice and Bob nodes. Each qubit generation setup hosts a rubidium quantum frequency conversion system and auxiliary equipment (e.g., a signal generator, delay controller, variable optical attenuator, beam splitter, feedback oscilloscope, combiner) and is connected to a dedicated fiber optic cable 325 (e.g., a single-mode long fiber) leading to node 70. Local node 60 has a detection subsystem, referred to herein as Dave 315, which is functionally identical to the Charlie node detector subsystem 350 of node 70. This configuration adds a 20 km loop in one of the detector input channels. The Charlie node at node 70 is configured to host the Hung-O-Mandel interference measurement setup 375. A path from node 60 is configured to be approximately 18 km long, traversing the local fiber optic loop infrastructure of node 70 (e.g., a second site), for phase randomization between channels. A polarization compensation subsystem 340 compensates for polarization modifications in the 70 km. The Charlie detection subsystem 350 hosts an SNSPD 372, a time-to-digital converter 374, and timing and control infrastructure 380.

[0102] Controllable quantum network nodes More specifically, in Figures 6A-6B In the embodiment depicted, there are four controllable nodes in the QEI network. Alice and Bob are optical-material interface nodes 310 and 320, respectively, located on node 60 (e.g., the first site). The two nodes share the same laser subsystem 330, which includes lasers with wavelengths of 795 nm, 780 nm, and 1367 nm and an associated locking system. The shared lasers are separated and sent to independent QM-QFC settings 311 and 321 in the Alice and Bob nodes, respectively. Each QM-QFC setting has its own independent acousto-optic modulator, electro-optic modulator, and optical attenuator to perform basic operations.

[0103] Node 60 (e.g., the first site) shares a network / timing switch 362, a controller 361, a sequencer 364, and a multi-channel delay generator 366. QM-QFC (Alice and Bob) nodes 310 and 320 also share a laser subsystem, including lasers with wavelengths of 795 nm, 780 nm, and 1367 nm controlled by a dedicated computer. The QFC qubit creation process is performed via an acousto-optic device and a variable optical attenuator (VOA) device that modulates each laser. Feedback is used to optimize the amplitude modulation signal to the background. The modulated laser signal is combined in an optical setup (e.g., combined optics 312 and 322 at the respective Alice and Bob nodes) and then sent to the QM-QFC system (see also...). Figure 4A (The combined optical device device 230 in the middle). Their outputs are connected to a dedicated optical fiber 325 that transmits quantum signals to node 70 (e.g., a second site).

[0104] exist Figure 6B The example implementation of the measurement node is shown in the figure. Figure 6B The measurement nodes shown can be located at node 70 (e.g., the second site) and node 60 (e.g., the first site). The measurement nodes can include at least timing and control infrastructure 380, a polarization compensation system 340, and a HOM detection system 350. Figure 6B Various other components are shown. Photon packets encoding qubits in their quantum states can be reached via optical paths (e.g., optical fibers), such as 70 km and 88 km paths, and are guided to the HOM detection system 350 via the polarization compensation system 340. The node controller 391 can be configured to control... Figure 6B The measurement node is shown in various aspects. Node 70. Network switch 392 can be configured to route signals between different components of the measurement node. Timer switch 393 can be configured to perform synchronization, such as synchronizing signals between measurement nodes.

[0105] In one embodiment, two optical paths implemented by optical fibers 325 and 326 can connect Alice setup 310 and Bob setup 320 to the measurement node. The two optical paths can have different distances. For example, the length of fiber 325 can be greater than the length of fiber 326. In one embodiment, fiber 326 can have a length of 70 kilometers (km) due to an approximately 18 km fiber loop 325a, and fiber 325 can have a length of 88 km. The fiber loop 325a can provide phase randomization between the two optical paths implemented by optical fibers 325 and 326.

[0106] The polarization compensation system 340 can be configured to compensate for the polarization of photon packets received from the optical path. In the polarization compensation system 340, the fiber loop 325 can be repeated to perform compensation simulating phase randomization between fibers 325 and 326. As an example, the polarization stabilization system 385 can use optical element 343 to guide a macroscopic QFC state (e.g., in the form of macroscopic light) to polarimeter 344 for measurement during the stabilization phase. Optical element 343 can be, for example, a computer-controlled mirror or optical switch. Optical component 343 can be controlled by a computing device or integrated circuit (IC), such as a field-programmable gate array (FPGA) in the polarization compensation system 340. Figure 6B As shown, optical element 343 can be controlled to guide the macroscopic QFC state toward polarimeter 344 or toward HOM detection system 350. In one embodiment, in response to completing polarization compensation, the optical element can be automatically removed or switched to allow the macroscopic QFC state to be guided to HOM detection system 350. Additional details regarding polarization compensation can be found in the further description below, such as Figures 7C to 7E The description.

[0107] The HOM detection system 350 may include various components for measuring photon packets and determining the indistinguishability between photon packets received by the measurement node. The HOM detection system 350 may include at least a HOM setup 375, an SNSPD 372, a sequencer 394, a delay generator 396, a time-to-digital converter (TDC) 374, and a PC 377. As an example, the measurement node may receive a first packet of photons from a first quantum memory and a second packet of photons from a second quantum memory. The first and second memories may be located in different settings. For example, the first memory may be a quantum memory in Alice setup 310, and the second memory may be a quantum memory in Bob setup 320. The first and second packets of photons may arrive at the HOM detection system 350 at different arrival times. In one embodiment, the different arrival times may be a result of different lengths of optical fibers 325 and 326.

[0108] The first and second packets of photons can be received by HOM setup 375. HOM setup 375 may include at least one beam splitter. HOM setup 375 can route the first and second packets of photons to SNSPD 372 via two local optical channels within HOM detection system 350. SNSPD 372 can determine the arrival times of the first and second packets of photons. As an example, SNSPD 372 can record photon detection events, such as the arrival of photons at SNSPD 372 and their arrival times via the two local optical channels. SNSPD 372 can output the photon detection events and arrival times to TDC 374, and TDC 374 can convert the arrival times into digital data for PC 377. In one embodiment, SNSPD 372 can be connected to a classical network to allow real-time monitoring and data acquisition.

[0109] In one embodiment, PC 377 can determine the difference between the arrival times of a first packet of photons and a second packet of photons. PC 377 can further determine the overlap rate between the first packet and the second packet of photons. To determine the overlap rate, PC 377 can determine a first arrival time of the first packet of photons within a predetermined time period, and a second arrival time of the second packet of photons within the same predetermined time period. If the predetermined time period includes both the first and second arrival times, or if photon detection events are detected in both the first and second packets of photons within the predetermined time period, PC 377 can record an overlap count. PC 377 can continue to determine overlap counts or overlap rates (e.g., overlap between the first and second packets of photons) for different time periods, for example, periodically at the same time intervals.

[0110] After a predetermined number of overlaps is reached, PC 377 can control delay generator 396 to add a delay to one or both of the optical channels of the first and second packets of received photons. The delay can be added to the optical channel between polarization stabilization system 385 and HOM setting 375, and / or can be added to the local optical channel between HOM setting 372 and SNSPD 372. PC 377 can repeatedly determine the overlap count with the added delay (e.g., determine a second overlap count). PC 377 can determine a relationship between a first number of overlap counts and a second number of overlap counts. Based on the determined relationship, PC 377 can determine the HOM visibility indicating the indistinguishability between the first packet and the second packet of photons. Additional details regarding the comparison of arrival times within a predetermined time period can be found in the further description below, such as... Figure 7A and Figure 7B The description.

[0111] In one embodiment, PC 377 can control delay generator 396 to adjust the delay based on the determined relationship to minimize the overlap rate. Minimizing the overlap rate can maximize the HOM visibility and indistinguishability between the first and second packets of photons. Furthermore, the difference between the average number of photons in the first packet and the average number of photons in the second packet can be set within a predetermined threshold that maximizes HOM visibility. In one embodiment, the average number of photons in the first and second packets can be defined or set within a pulse time envelope.

[0112] Figure 6C A flowchart depicts an example process 299 that can be performed by a measurement node according to an embodiment. Process 299 may include one or more operations, actions, or functions as shown in one or more of blocks T2, T4, T6, T8, T10, and / or T12. Although shown as discrete blocks, depending on the desired implementation, the various blocks may be divided into additional blocks, combined into fewer blocks, eliminated, executed in a different order, or executed in parallel.

[0113] Process 299 can be performed by a measurement node (e.g., measurement node 70 described herein) to determine the degree of indistinguishability between qubits and / or photon packets (e.g., in the form of laser light). Process 299 can begin at block T2. At block T2, the measurement node can receive a first packet of photons from a first quantum memory. Process 299 can proceed from block T2 to block T4. At block T4, the measurement node can receive a second packet of photons from a second quantum memory. In one embodiment, the first packet of photons can be received from the first quantum memory via a first optical path having a first distance. The second packet of photons can be received from the second quantum memory via a second optical path having a second distance different from the first distance. In one embodiment, the first and second packets of photons can be received by a HOM detection system, and the HOM detection system, the first quantum memory, and the second quantum memory are located at the same location. In one embodiment, the same location includes the first quantum memory, the second quantum memory, and the HOM detection system as a first location. The first quantum memory can receive the first packet of photons from a first light source located at a second location different from the first location, and the second quantum memory can receive the second packet of photons from a second light source located at a third location different from both the first and second locations.

[0114] Procedure 299 can proceed from box T4 to box T6. At box T6, the measurement node can determine the first arrival time of the first packet of photons. Procedure 299 can proceed from box T6 to box T8. At box T8, the measurement node can determine the second arrival time of the second packet of photons. Procedure 299 can proceed from box T8 to box T10. At box T10, the measurement node can determine the difference between the first and second arrival times. Procedure 299 can proceed from box T10 to box T12. At box T12, the measurement node can determine the overlap rate between the first and second packets of photons. Procedure 299 can proceed from box T10 to box T12. At box T12, the measurement node can determine the HOM visibility based on the overlap rate and the difference between the first and second arrival times. HOM visibility indicates the indistinguishability between the first and second packets of photons.

[0115] In one embodiment, the measurement node can compensate for the polarization of a first packet of photons and the polarization of a second packet of photons. In another embodiment, the measurement node can use multiple optical elements to compensate for the polarization of the first and second packets of photons to guide macroscopic light to a polarimeter for measurement, and automatically remove multiple optical elements to release the first and second packets of photons to the HOM detection system.

[0116] In one embodiment, the difference between the average number of photons in the first packet and the average number of photons in the second packet can be within a predetermined threshold that maximizes HOM visibility. In another embodiment, the average number of photons in the first packet and the average number of photons in the second packet can be defined within a pulse time envelope.

[0117] In one embodiment, determining the overlap rate may include determining a first arrival time within a time period, determining a second arrival time within a time period, and recording an overlap count in response to determining that the first and second arrival times are within the time period. In one embodiment, the first arrival time may be a photon detection event in a first set of photon detection events in a first channel of a first packet of received photons, the second arrival time may be a photon detection event in a second set of photon detection events in a second channel of a second packet of received photons, and the overlap count is within the number of overlap counts. In one embodiment, the number of overlap counts may be a first number of overlap counts. The measurement node may add a delay to at least one of the first and second channels. The measurement node may also utilize the added delay to monitor the first set of photon detection events in the first channel and the second set of photon detection events in the second channel. The measurement node may also determine a second number of overlap counts based on the monitoring with the added delay. The measurement node may also determine a relationship between the first number of overlap counts and the second number of overlap counts.

[0118] In one embodiment, the measurement node can adjust the delay based on the relationship between a first number of overlap counts and a second number of overlap counts to minimize the overlap rate, wherein minimizing the overlap rate maximizes HOM visibility and indistinguishability.

[0119] Distributed timing and synchronization The timing infrastructure within the QE interface plane ensures successful network operation, particularly for non-local or interference-based protocols such as HOM, where interference quality quantifies success. To ensure precise time synchronization between remote nodes, White Rabbit bidirectional time transfer technology is employed along the 70km fiber optic link connecting the quantum network nodes. Each node has a WR timing switch (e.g., Figure 6B The timing switch 393 delivers a 10 MHz analog synchronous clock signal and a phase-locked loop trigger signal with one pulse per second.

[0120] To evaluate the performance of the timing system, the system measures the phase-locked pulse (PLP) between Alice and Bob nodes at node 60, which is synchronized with the WR source at Charlie in node 70. This setup generates a picosecond network. Time jitter 327, such as Figure 7A shown in . Specifically, Figure 7A A histogram of jitter events in a 70 km shared clock network is shown, where Charlie (at node 70) is a tree configuration connecting Alice and Bob (at node 60). The master clock. Bob's time frame relative to Alice's time frame shows the jitter of ps. Illustration: Sample delay diagram between the three-node configuration of the White Rabbit device and two-node 60 clocks, where TDC is the time-to-digital converter element.

[0121] Effective network time jitter is also characterized by the impact of protocol-dependent QEIP elements. Telecommunication laser pulses are generated at node 60 using an electro-optic modulator driven by a signal generator, where a local clock is phase-locked to the network timing system WR clock. After propagation through 70 km of fiber, the system compares the pulse arrival time at node 70 with a similar clock signal. Figure 7B Histogram 335 shows the temporal differences between these pulses over 12 hours, and specifically, after the 12-hour integration time, the histogram of jitter events in the complete node 60-node 70 70 km QN fiber link. In the example, a Gaussian distribution of the FWHM with 3.4 nanoseconds was obtained, which is three orders of magnitude smaller than the time width of the telecom photons generated by the FWM. Furthermore, the Allan bias associated with long-distance jitter measurements was systematically estimated. As a function of the changing query time, such as Figure 7B As shown in illustration 345, the Allan bias is observed to follow... This trend means that effective quantum network time jitter is stable and predictable over intervals of less than 12 hours. This level of time synchronization allows the control plane to accurately configure the QE interface plane to execute HOM protocol sequences across long-distance (e.g., 158 km) networks and provides a basis for non-local QN operation.

[0122] Regarding the Allan bias of QN clock jitter, normalized jitter is defined as... ,in It is the pulse repetition rate. This is the jitter measurement. The Allan variance is defined according to the following equation S1: (S1) in L is the time interval for each query. The number of data points in the data. and . It lasts for 12 hours, and It represents the total number of data points collected.

[0123] polarization compensation Maintaining a consistent polarization base across nodes ensures photon indistinguishability; in some embodiments, the polarization compensation process is performed by the CP 120 and QEIP 130 interface planes. This process dynamically compensates for polarization drift across the entire network to mitigate polarization fluctuations caused by random birefringence resulting from thermal variations, mechanical stress, fiber core irregularities, and other varying environmental and material inhomogeneities. Light generated by a CW1324 nm FWM is transmitted to characterize and compensate for polarization variations before HOM measurements are performed using the quantum states generated by the QM-QFC. This compensation is facilitated by a prototype device that employs machine learning to modify the birefringence in the compensation fiber loop at the termination of the 70 km fiber connecting nodes 60 and 70. Feedback from the polarimeter informs the compensation procedure. In some embodiments, an intermediate field-programmable gate array (FPGA) allows the controller to monitor the compensation state and efficiently manage the scheduling.

[0124] As an example, the complete polarization compensation system was characterized as a proof-of-principle over 12 hours, with compensation applied every 15 minutes. The system measures polarization fluctuations by obtaining the Stokes vector of the light generated by four-wave mixing (FWM) during the free-run mid-time and after the compensation procedure.

[0125] Figure 7C A graph showing the distributed polarization state between nodes 60 and 70 is plotted, where compensation is performed every 15 minutes within a 12-hour integration period. PS is composed of three normalized Stokes parameters. And fidelity table The upper graph 342 shows a close-up of the stable period 348 (around midnight) and the period 352 (early morning) with more fluctuations. Figure 7C The correlation between polarization stability and time of day is further illustrated. Compensation is set using initial Stokes parameters. and Correcting the initial horizontal polarization of the FWM-generated light. The fidelity of the corrected received signal is calculated as follows: in This is the first Stokes parameter. The fidelity achieved after each compensation step is... Figure 7E As shown in the image.

[0126] In addition, the network downtime required to implement compensation was assessed. Figure 7D Histogram 355 is plotted, which shows the statistical distribution of compensation time (e.g., every 15 minutes) measured over 12 hours, close to... A cluster time of 358 seconds indicates a failed compensation attempt. Stabilize the transmitted PS to the desired state. Required time distribution. Illustration 363 shows that no correlation with time of day was observed during the 12-hour observation period.

[0127] Finally, the system has determined the settling time, which is defined as the time it takes for the fidelity to decrease to 0.97 after compensation has been performed. Considering long-distance HOM service scenarios, 0.97 is chosen as the example lower limit of 365, where two symmetrical channels of weakly coherent pulses are used to obtain... HOM visibility, of which It is the fidelity of the channel relative to each other. These measurements are in Figure 7E The figure illustrates the polarization fidelity measurement 368, which is performed with feedback activated every 15 minutes during a 12-hour collection period. It is noted that during the high-stability period of long-distance fiber optics, the fidelity typically remains above the defined threshold 365 for over 200 seconds. Based on these results, a compensation protocol was chosen to be activated after a three-minute free-drift time interval. This characterization allows for high HOM visibility throughout the entire duration of the quantum communication experiment while minimizing network downtime, for example... Figure 7C Box 346 in the middle. Figure 7E The free drift time 372 is further shown after the polarization fidelity is maintained above 97% after compensation.

[0128] Control plane implementation Return to reference Figure 3 CP 120 generates commands for all classical and quantum devices distributed across the QEI network via QEIP 130 and defines primitive functions for creating QN protocols. CP 120 addresses the following issues: (i) interfacees CP120 with QAP 110 and QEIP 130 using the QE-API, (ii) runs QN primitives for physical centers associated with the time evolution of quantum variables that define the performance of quantum network devices, and (iii) runs QN protocols for physical centers that manipulate the Hamiltonian evolution of quantum devices and measurements.

[0129] As an example of this concept, the system executes the HOM QN protocol, an operation that must be performed to confirm that the QN is ready to establish an entangled link. Since the QN protocol is implemented through the interaction of CP 120 and QEIP 130, the HOMQN protocol is implemented by implementing the southbound QE-API 133. Using the Virtual Instrument Software Architecture (VISA) protocol and a custom device communication standard, QE-APIs, including Python libraries, were developed to uniformly address and control network devices based on functionality. These QE-APIs enable the development of an eight-step software process used by the control plane to orchestrate the QEI's operations for running the HOM protocol, for example, as... Figures 9A-9BAs shown. These primitives / operations are run on QEI to extract optical count measurements at the end nodes, thereby verifying high-visibility HOM interference. These QN primitives include modifications to the parameters of the frequency-converted FWM Hamiltonian. (See Equation 2).

[0130] In some embodiments, a set of application programming interfaces (APIs) is used to control the operation of each quantum node over a classical network to orchestrate the operation of various devices on the network infrastructure and enable quantum information flow. In some embodiments, the quantum setup and subsystems are driven and monitored by devices (e.g., signal generators, configurable power supplies, oscilloscopes, time-to-digital converters, etc.) that can be connected to the classical network via standard Ethernet, USB, or other interfaces. A series of APIs communicate with device drivers and low-level software layers to control system components over the network. In some embodiments, these drivers overlap with the Virtual Instrument Software Architecture (VISA), an industry-standard API for communicating with instruments via Ethernet, GPIB, and USB interfaces. For example, the APIs are developed to control devices on top of Python, using Python wrappers for VISA, such as PyVISA. For example, a Python package with all associated drivers and built-in search and identification protocols can be implemented. A characteristic of the APIs controlling devices is device agnosticness: they are designed so that higher-level quantum network control protocols are independent of the brand and model of a single device.

[0131] In some embodiments, the Quantum Enablement (QE) Application Programming Interface (API) defines how the control plane communicates with the QE interface and the application plane. The Southbound QE-API includes drivers that handle communication between the controller and all device and subsystem controllers on the QE interface plane. In some embodiments, these drivers may be written in Python and based on the Virtual Instrument Software Architecture (VISA) protocol and custom device communication standards. Depending on their functionality, these libraries follow a unified design pattern for controlling networked devices. Figures 9A-9B The example eight QE protocol steps shown are constructed from these drivers.

[0132] The Northbound QE-API consists of commands (e.g., Python commands) written over the Example 8 protocol procedures. They can extract measurement and state information, including average photon number, temporal photon shape, and HOM visibility, along all procedure steps. In some embodiments, the techniques disclosed herein also develop dashboards / graphical user interfaces (GUIs) to present relevant information using the Northbound QE-API when executing the QN protocol.

[0133] Execution of the HOM protocol The implementation of QN primitives and protocols highlights the orchestration between QDP 140, QEIP 130, and CP 120. Within the context of the whole-network HOM (Homme-O-Mandel) visibility inspection protocol, Figures 8A-8B This arrangement is presented in the document. To implement the HOM indistinguishability protocol, CP 120 orchestrates and optimizes the functionality and interactions of QN primitives, which is accomplished via the QE protocol using physically related subsystems within the network. In some embodiments, Figures 8A-8B A streamlined view of the network hierarchy among the three nodes is presented, and how the controller adjusts the active network across QE protocols to facilitate the execution of QN primitives that form the QN protocol is described. Figures 8A-8B In this code, the following symbols are used: SG: Signal Generator; L. Cont.: Laser Controller; L.: Laser; WR: White Rabbit; ADG: Arbitrary Delay Generator; OSC: Oscilloscope; Orch.: Orchestrator; TDC: Time-to-Digital Converter; SNSPD: Superconducting Nanowire Single-Photon Detector; QNCP: Quantum Network Control Protocol; Pol: Polarimeter; I / OM.: On / Off Mirror; Pol. Stab: Polarization Stabilizer; PC: Computer.

[0134] Figures 8A-8B The implementation of the QE interface plane 800 is partially shown: the node 70 / node 60 QEI testbed has two identical co-located nodes at one location (e.g., node 60) and a third node at the node 70 location. Figures 8A-8B The device shown is encoded by the functions, their connectivity, and their grouping in the quantum optical system (quantum) setup (802) and the quantum optical subsystem (804), with each node (depicted separately here) being encoded separately. like Figure 8A As shown, the QE interface plane 800 includes a domain controller 801 configured to communicate with node controller 811 and Alice and Bob nodes, and to instruct the node controllers to initialize all systems they supervise, such as establishing communication with all systems and subsystems of their nodes, turning on lasers, etc. As an example, the domain controller provides subnet control signals 808 and subnet timing signals 809 for orchestrating quantum operations across multiple nodes via the northbound interface of its corresponding node controller. Node controller 811 controls a set of application layer protocols via a control subset connection, which leverage the capabilities of a hybrid quantum internet stack to orchestrate the operation of various devices on the network infrastructure and enable quantum information flow. In one embodiment, the protocol may implement a quantum network control protocol (QNCP) driver group 813 that controls signal generator devices labeled SG1, SG2, which generate corresponding pump fields. The acousto-optic device drives the amplitude modulator (AM) and further controls a delay controller labeled DC1, which drives a variable optical attenuator (VOA). The QNCP driver group further controls an oscilloscope device labeled OSC1, which provides monitored readings as feedback to optimize the signal, such as amplitude modulation; and controls an arbitrary delay generator labeled ADG to instruct ADG to assign triggers to the SG via timing connection 816 for qubit generation setup. Another driver 823 controls a sequence arranger labeled Orch. It receives precise timing signals from a white rabbit timing switch 820 for orchestrating the operation of the QEI running the HOM protocol.

[0135] like Figure 8A As further shown, at each Alice and Bob node, an additional QNCP driver 825 controls a laser controller 828, which in turn calls an additional laser subsystem driver 830 to control each of the 795 nm, 780 nm, and 1367 nm lasers used in the quantum optics subsystem.

[0136] like Figure 8A As further shown, additional QNCP drivers 832 and 834 instruct the time-to-digital converter (TDC) and single-photon detector (e.g., a superconducting nanowire single-photon detector (SNSPD)) to begin data collection at the quantum optical measurement subsystem at each Alice and Bob node, respectively. As shown, the SNSPD is connected to the TDC, supervised by its dedicated PC, via a QNCP API 837. An orchestrator managed by a WR switch 820 provides timing connections to the TDC. Similarly, at the Charlie node in the second location, node controller 852 receives similar timing and control subnet signals 808 and 809 to perform similar actions at the quantum optical setup (measurement) 804 in the second location, including providing timing control at the clock of the white rabbit switch device 860. The Charlie node optical setup measurement subsystem 804 uses QNCP drivers (and APIs) managed by the primitives to control the orchestrator device and the ADG, TDC, OSC, and SNSPD devices in the same manner as at the Alice and Bob nodes.

[0137] like Figure 8BAs further shown, at the Charlie node, the node controller 851 drives the QNCP driver 862 to operate the field-programmable gate array (FPGA) device for polarization control (stabilization subsystem), for example, to initiate the polarization matching process. The FPGA calls the QNCP API 865 to control the polarization stabilizer 870. The polarization control subsystem further employs driver 875 to control a computer-controlled mirror (I / O mirror) used to guide photons to the polarimeter for measurement during the stabilization period.

[0138] The (HOM) visibility check protocol begins by ensuring that the controller can communicate with the network elements corresponding to the Hamiltonian parameters in the FWM system: Alice and Bob's qubit generation (controlling quantum variables). and Time evolution), control field control (controlling the variables of each QM-QFC) and Time evolution in FWM Hamiltonian), polarization-stabilized subsystems (guaranteeing quantum variables) and High-fidelity preservation after long-distance propagation) and the HOM measurement subsystem (measuring quantum variables) (overlap between) (see) Figures 8A-8B ).exist Figures 9A-9B The text details the evolution of QN primitives and the interaction between them and the execution of the HOM QN protocol, depicting the HOM protocol and the highlighted network primitives executed by the active QEIP components.

[0139] Quantum Application Plane Implementation QN services are executed by physically running the QN protocol, utilizing interactions across all network planes via QAP. Users or higher-order network processes initiate the QN service through the Northbound Interface (NBI), sending the request to the CP. Based on the QN service request, the CP then issues a series of commands to the QEIP via the SB QE-API, enabling the physical implementation of the QN service at the QDP.

[0140] High Visibility Hung-Omandel Quantum Network Service An example of a robust QN service implemented by QEIP components is the long-distance verification of high-visibility HOM interference using an optical-matter quantum interface. This capability can form the basis for implementing more advanced QN protocols, such as Cabrillo entanglement generation, Duan-Lukin-Cirac-Zoller entanglement creation, memory-assisted entanglement swapping, and quantum repeater-assisted teleportation. As demonstrated by the Peres Horodecki criterion and CHSH bounds (e.g., the John Clauser, Michael Horne, Abner Shimony, and Richard Holt (CHSH) inequality), successful execution of high-visibility HOM interference at remote network nodes can serve as a metric for the network's ability to distribute entanglement and perform teleportation. These criteria directly link HOM visibility to the quality of entanglement generation and delivery.

[0141] To benchmark the quality of the QN service, a framework was established that correlates network flow with the performance of quantum measurement operations. For the special case of long-distance, high-visibility HOM QN services, the system calculates the second-order correlation between the outputs of the beam splitters at Charlie or Dave and compares it with an analytical model to quantify the visibility of the interference effect. Assuming the pulse sequence and frequency linearity are Gaussian, the interference visibility can be evaluated according to equation (2) as follows: (2) in , It is the time difference between related events. It is the pulse repetition period. and The optical frequencies characterizing the time pulse and the incident pulse, It is the difference in center frequencies between the inputs, and It interferes with visibility.

[0142] As can be seen from equation (2), the HOM interference will exhaust the... The characteristics of the rate within the "center" peak centered on the location. When the pulse is much shorter than the CW coherence time, the pulse modulation determines the linewidth. The distribution is proportional to the center peak. The size has been reduced. For intermediate states with pulse widths and CW coherence times comparable to those of the pulse width, the center lobe of the distribution can exhibit a bimodal shape, as shown in the data below. The quality factor was obtained by fitting the HOM experimental data. The data was collected to verify long-distance high-visibility HOM interference and complete the HOM QN service.

[0143] Long-distance high visibility HOM QN service like Figures 10A-10BAs shown, an example HOMQN service that can be executed in a hierarchical (e.g., 158 km) QEIP configuration is depicted. For characterization purposes, an experimental configuration, such as a QEIP testbed 1000, is first used within the campus of a first site at node 60, with an HOM measurement station at the Dave node 1002 of the first site. This configuration uses a fiber optic loop 1010 (e.g., ) that transmits the first local location in node 60 to a second local location in node 60 over a distance of 20 km. Figure 10B In the loop 1010), perform HOM visibility check QN service.

[0144] More specifically, a four-node QN was established for long-distance, high-visibility HOM QN services. Two quantum memory and frequency conversion settings, namely Alice setting 1030 and Bob setting 1040, are jointly located at the first site campus associated with node 60 and are independently connected to the network. Each of Alice setting 1030 and Bob setting 1040 may include Figure 4A The system 200 shown includes interference setups and telecom-compatible single-photon nanowire detectors (SNSPDs) at Charlie station 1002 located at the second site node 70 and Dave station 1004 located at the first site campus at node 60. Each of Charlie station 1002 and Dave station 1004 may include... Figure 6B The HOM detection system 350 shown here transmits quantum information, for example, at the bottom layer configuration 1001, and quantum enable information, for example, at the middle layer configuration 1003. Other fibers transmit classical timing triggering, network state, and ordering information, for example, at the top layer configuration 1005. Figures 10A-10B The layers 1001, 1003, and 1005 shown represent the coexistence of three types of information required for the functionality of a quantum network: classical, quantum enablement, and quantum.

[0145] More specifically, in stack-driven quantum memory (QN), such as Figure 10A As shown, top layer 1005 corresponds to the classical control network layer for user-defined control and fast feedback. Within top layer 1005, state-of-the-art networking utilizes the concept of Software-Defined Networking (SDN) to manage and control long-distance information transmission and processing. These concepts are applied to QEIP, where a digital device network manages and controls quantum devices on demand. Furthermore, higher-order management concepts are incorporated to distribute photons created in quantum memories across the network topology.

[0146] For example, the classical network portion of the top layer 1005 of the QEIP provides classical information for establishing nodes for quantum communication and is configured to distribute the necessary control command sequences responsible for performing quantum network operations, while also accommodating the communication required for monitoring and managing the multiple interconnected devices contained within the quantum network. Reflected in the node top layer 1005, the QE control plane employs node controllers, and the network switches, playing a central role, use their Southbound Interfaces (SBIs) to drive the configuration of devices set up in the quantum optics system (i.e., devices that require direct command sequences from their node controllers to operate, such as initializing all systems they supervise, establishing communication with all systems and subsystems at the nodes, turning on and controlling lasers, signal generators, etc.) and further interface with quantum optics subsystems (e.g., those operating via intermediate controllers (computers / PCs / FPGAs) hosting the necessary control software and / or drivers). For example, this layer 1005 provides classical timing triggering, network state, and sequencing information. In addition, this layer provides synchronization signals, such as a synchronization clock signal and a phase-locked loop trigger signal 1015 provided to the QE interface plane at layer 1003, using a timing switch (WR switch), an orchestrator, and an ADG. Figure 10A As further illustrated, a standard dense wavelength division multiplexing (DWDM) system implements multiple independent communication channels. For example, two DWDM channels are used for White Rabbit (WR) protocol connections, while other DWDM channels are used to interconnect the master network switch in each node. Servers and network-compatible electronics connect to each switch, thereby enabling the control operation of the QEIP testbed. In a larger-scale Internet, multiple domains orchestrate the execution of quantum operations through orchestrated applications that communicate with the domain controller via their NBIs.

[0147] like Figure 10A As further shown, QEI layer 1003 includes devices supporting time, phase, and polarization simulation measurements, including the generation and transmission of light generated by a CW 1324 nm FWM, which is transmitted to characterize and compensate for polarization variations. This layer 1003 is specifically designed for long-distance connections to maintain quantum coherence with core functions, including supporting time-sensitive operation and real-time compensation for environmentally induced fluctuations in qubit transmission parameters. The integrated time resolution of the long-distance synchronization system is less than 100 ps, ​​far lower than the time envelope of photons propagating in the network. Furthermore, a feedback mechanism for preserving the polarization state propagating in single-mode telecommunication fiber was implemented. In QEI layer 1003, quarter-wave (λ / 4) and half-wave (λ / 2) elements, as well as a polarimeter, can manipulate the polarization state before transmission, and a fiber squeezer can apply pressure to the fiber in the receiving node to act as a variable waveplate to manipulate the polarization state of light passing through the fiber.

[0148] like Figure 10B As shown, the quantum network layer 1001 includes interconnected quantum devices in which quantum information can be transmitted, buffered, and processed, including the quantum hardware required to generate entanglement using robust quantum interference. The quantum network layer 1001 includes a room-temperature quantum memory, a qubit detection system, and photon quantum signal transmission. An absorptive atom quantum memory compatible with telecommunications infrastructure is used to demonstrate the coherent frequency conversion from photons with near-infrared frequencies generated in the quantum memory (780 nm / 795 nm) to 1324 nm in the telecommunications O-band. A HOM detection setup 1050 at the Dave and Charlie nodes is further shown, i.e., HOM interference measurement is performed.

[0149] In one embodiment, the three-layer optical network forming the QEIP testbed 1000 realizes a hybrid network stack that simultaneously accommodates quantum enablement and quantum manipulation. The components and functions of the hybrid stack can be divided into... Figures 10A-10B The three stack protocol sets associated with each role in the optical network described are: 1) a quantum stack, which enables communication between quantum devices to perform the key operations required to achieve entanglement generation and distribution; 2) a quantum-enabled stack, which combines the standard TCP / IP stack with time-sensitive principles to establish a precise sequence for controlling quantum devices and compensating systems, thereby enabling high-fidelity transmission of qubits; and 3) a classical stack, which is the standard TCP / IP stack, enabling classical devices that control the QN to interconnect. Figure 3 The control plane 120 includes protocols within the classical and quantum-enabled stacks required to control and orchestrate operations at the device, node, domain, and network levels.

[0150] When performing HOM visibility check QN service, the QEI architecture is used to drive experiments to create independent quantum state sequences in each QM-QFC. Figures 9A-9B The network primitives defined in [the code] control sequencing in the following ways (see [link to full sequence]). Figure 11A ): a) Use CP and QEIP to execute Initialize_Procedure() and Characterize_Optical_ Modulators() The QE protocol is used to characterize 780 nm qubit modulation. For example... Figure 9A As shown, Initialize_Procedure() The QE protocol 902 operation method steps are as follows: via Southbound QE-API 133 ( Figure 3 Establish communication between the domain controller and relevant settings and auxiliary systems; turn on the laser; enable the domain controller to set the pulse repetition rate according to business parameters; and connect the pump field ( Set them to be equal. For example... Figure 9A As shown, Characterize_Optical_Modulators()The QE protocol 904 operating method steps are as follows: The domain controller runs a characterization and optimization sequence for the optical modulator and attenuator at the qubit generation setting via signal generation and acquisition (photodetector) devices. The associated primitives are... .

[0151] b) A 1324 nm photon beam was generated using a QFC pump, and the average photon number of the QM QFC output was verified using QDP, CP, and QEIP to perform [the desired operation]. Charaterize_Rates() QE protocol, characterizing and The associated QN primitive. This produces a pulse repetition rate and time envelope of 125 kHz. .like Figure 9A As shown, Charaterize_Rates() The steps for operating the QE protocol 906 are as follows: Start the domain controller at the qubit generation settings. Pulse operation. Charlie measured the FWM output photon rate of the subsystem. It is characterized and roughly balanced.

[0152] c) Execute using QDP, CP, QEIP, and QDP. Match_Timings() and Balance_Powers() The QE protocol prepares for long-distance HOM data collection over thousands of production cycles. This generates an average photon rate of approximately 800 kHz for both Alice and Bob conversion channels at the HOM measurement beamsplitter 1006 at the Dave station (e.g., at node 60), thus preparing for... Related primitives. For example... Figure 9A As shown, Match_Timings() The steps for implementing QE protocol 908 are as follows: Enable the domain controller to use the measurement subsystem to extract the time histograms of the two FWM output arms. ; and use an arbitrary delay generator 366 ( Figure 6A The domain controller causes the time envelopes of the two channels to overlap. For example... Figure 9B As shown, Balance_Powers () The QE protocol 914 operating method steps return to pulse operation and use time histograms to characterize and finely balance the FWM output photon rate at Charlie's measurement subsystem. .

[0153] d) Use CP and QEIP to run Evaluate_polarization() and Match_Polarizations() The QE protocol verifies polarization preservation across long-distance networks. For example... Figure 9B As shown, Evaluate_polarization()The QE protocol 910 operation method steps include: causing the domain controller to return the network to continuous wave operation at a rate suitable for the polarizer settings; and causing the domain controller to trigger the polarization compensation system to route the optical path to the polarizer, and evaluating the frequency at which compensation should be scheduled. Furthermore, as... Figure 9B As shown, Match_Polarizations() QE Protocol 912 performs similar method steps to cause the domain controller to return the network to continuous wave operation at a rate suitable for the polarizer settings; and to cause the domain controller to trigger the polarization compensation system to route the optical path to the polarizer and match the polarization of the path.

[0154] e) Execute using QDP, CP, QEIP, and QDP. Run_Experiment() Quasi-real-time long-distance HOM coincidence analysis using the QE protocol. This makes the average photon number at the input port of the HOM BS for both Alice and Bob... / pulse. For example... Figure 9B As shown, Run_Experiment() QE Protocol 916 operates in a manner that engages the controller with the qubit generation setup to send pulses at the minority-photon level and initiates the measurement subsystem to acquire data from the superconducting nanowire single-photon detector (SNSPD) and TDC. The controller generates an overlay map and calculates the interference quality—visibility.

[0155] Figure 11A This is graph 1100, depicting the orchestration sequence used for QM QFC generation and long-range HOM interference. Graph 1100 shows the temporal dynamics of each node and its devices within the network.

[0156] Figure 11B Graph 1115 depicts the results of the HOM QN service at Dave node 1002 and partially depicts the results of the 1324FWM HOM pulsed quantum interference experiment for the 20km QEI configuration operation at node 60. Inset 1117 shows the results for CW input (continuous wave HOM), and graph 1115 shows the pulsed results, demonstrating the main features predicted by the model. Figure 11B The fit between the experimental data and the equation is also shown. (2) From which 47% visibility can be determined, demonstrating the robustness of the QN service over a distance of 20 km.

[0157] Figure 11C , 11DFigure 11E depicts 1324 FWM HOM pulse quantum interference experiments operating at node 60 (e.g., the first site) and node 70 (e.g., the second site) for a long-distance (e.g., 158 km) QEI configuration. Detailed data at Table 1 show measurements of different average photon numbers at the inverter outlet. Errors are calculated as the standard deviation of 20 averages. Each dataset corresponds to 3 minutes of data collection (18 million pulses transmitted).

[0158] Long-distance, high-visibility HOM service with stack control, e.g., 158 km. The indistinguishability of telecom polarization qubits converted in two independent QM-QFCs using the HOM interferometer experiment has now been demonstrated, with one arm of the interferometer measuring 70 km and the second arm measuring 88 km.

[0159] Figure 11C This is a graph 1125 depicting the results of HOM QN service for pulse input over a long distance (e.g., 158 km), where... and The average number of photons at the output of each QM-QFC is defined in a Within the Gaussian pulse time envelope FWHM. The total loss through two long-distance settings (QM-QFC output to SNSPD input) was measured as: for a link of And for the longer arm After long-distance propagation, the system obtains the pulse of each pulse from both the Alice and Bob conversion channels at the HOM measurement beam splitter at node 70 (e.g., at node 70 (second site)). The average number of photons was measured. The HOM (Homogeneous Origin and Mechanism) coincidence rate was measured relative to the arrival time of photons in both detectors. Coincidence within the temporal region of interest (ROI) was post-selected with a width of 93.4 ns (24 s divided into 257 bins). Desired modulation in the coincidence rate was observed, exhibiting a minimum for initial identical polarization and reaching a maximum corresponding to the coherence time of uncorrelated photons beyond the FWM (Frequency-Wide Motion) process. Figure 11C The fit between the experimental data and equation (2) is also shown. The visibility of the interference HOM was measured as and FWM spectral width is kHz. The error is calculated as the 68% confidence interval of the fitted curve. Before collecting pulse HOM data, the system verifies the HOM settings for continuous wave HOM service.

[0160] Figure 11C The illustration shows the conversion signal of Alice and Bob at the HOM measurement beam splitter depicted in Noe 70 (e.g., the second site). The curve 1127 shows the results of a HOMQN service with an average photon rate of kHz for a CW input over a long distance, for example, 158 km. Figure 11C-11E The fitting of the experimental data is also shown, from which it can be determined HOM visibility and A bandwidth of kHz.

[0161] Figure 11D-11E The figures 1130 and 1140 respectively depict the results of HOM QN service over long distances (e.g., 158 km) for different input photon numbers per pulse at the output of the QM QFC. For all three cases, the pulse repetition rate was 100 kHz, and statistical analysis was performed for each case with an integration time of 1 hour. Polarization compensation was performed every three minutes. The main data obtained from these measurements are summarized in Table 1. Based on the data fitting, the system obtained a characterization of the HOM QN service quality. The system obtained... and The photon spectrum FWHM width, and the corresponding photon FWHM pulse width are and The system probes the repeatability of the stack-driven HOM QN service. The system further measures... and The HOM visibility indicates that good visibility of the service is maintained when we approach the true single-photon level at the output of QM-QFC.

[0162] Table 1 As shown in Table 1, the data from the three pulse HOM services is displayed in Figure 11. and It is the estimated number of photons per pulse leaving node 60 (e.g., the first station). The number of photons per pulse in each quantum channel at the NPBS input port is measured at node 70 (e.g., the second station). It is based on the visibility fitted from equation (5). Is The overlap rate is obtained from the fitting. The error is calculated as the standard deviation of the mean of the 20 datasets.

[0163] These experimental measurements allow us to evaluate the performance of QEI, for example, when applying the original Cabrillo scheme to generate quantum memory entanglement over long distances. The first quality factor is the long-distance HOM visibility of the single-photon level output at the QM-QFC site, measured at the Charlie node. Based on the data given in Table I, this is estimated to be approximately 47%. Assuming further reduction in detector noise and that the single photon has the same fidelity as the coherent state, the expected single-photon HOM visibility is 94%, far exceeding the 33% limit of entanglement generation by the Peres Horodecki standard and also surpassing 71% of CHSH, necessarily requiring matter-matter entanglement to perform Bell inequality violation experiments. The second quality factor is the two-photon coincidence rate of the single-photon level input, whose lower limit can be estimated to be approximately [missing value]. For long-distance experiments, this estimate is competitive with the two-photon rates measured in state-of-the-art long-distance matter-matter entanglement experiments.

[0164] Given these results, the QN architecture paradigm and QEI infrastructure can be extended to perform quantum memory entanglement experiments over unprecedented distances in deployed optical fibers. These extensions will include QAPs that run entanglement-generating QN services in quantum memories, with the following additions. First, at the QDP level, the QFC scheme is scalable to directly generate entanglement with photons in the collective states of 1324 nm and QMs. This can be accomplished by correlating the polarization state of the generated 1324 nm photon with the polarization state of the resulting intermediate magnetic atom sublevel. Second, after the photon has propagated over long distances in the CP level, a Bell state projection QN service is performed to modulate the generation of entanglement between the magneton states of remote QMs. This measurement utilizes further enhancements to QEIPs, including allowing the QE-API to run undisturbed for hundreds of hours and phase stabilization of the entire quantum network testbed, which can be achieved by monitoring long-distance HOM interference services.

[0165] Further improvements to QDP could include long QM coherence times on the order of milliseconds, allowing for long-distance transmission of telecommunication photons and the transmission of Bell state results across quantum-enabled networks. Under these conditions, QAP could potentially verify the entanglement generated between QMs by recovering the states of QMs to entangled photon states and reconstructing their density matrix.

[0166] This disclosure describes an embodiment of the design, deployment, and implementation of a first instance of a QEI network connecting a QM-QFC atomic ensemble over a long distance (e.g., 158 km) of deployed optical fiber. Using a novel QN design paradigm, a stack-driven ubiquitous QN service has been demonstrated to provide long-distance, robust HOM interference with high visibility. This QN paradigm design can be applied to demonstrate further scalable long-distance QN services within current three-node QN infrastructures, including the transmission of polarization entanglement generated by highly repetitive sources of entangled photons and the storage of telecommunication polarization entanglement using a remotely located quantum memory capable of predicting the storage of entanglement using non-destructive measurements and quantum state tomography. Further advanced experiments will lay the foundation for the realization of stack-driven long-distance quantum repeaters.

[0167] Quantum frequency conversion theory in rubidium In this embodiment, the quantum frequency conversion system uses heated rubidium vapor in a glass chamber. The system is modeled using an ensemble of atoms within the cavity, and input-output theory is applied. Ultimately, the system reaches the bad cavity limit. The system's Hamiltonian is described as... The unperturbed Hamiltonian is defined according to equation S2: (S2) in These represent different atoms in the ensemble. The ground state of the atom is set to zero energy. Here... , and The 780 nm and 1324 nm modes within the cavity are represented. The interaction terms under the dipole approximation, in the form of coincident S3, are as follows: (S3) In the current fourth-order Hilbert space (see...) Figures 7A-7E ), (S4) Among them, atomic state is selected. The phase makes the dipole matrix elements real. The pump field is treated as a classical field, and the system quantizes the two weak fields such that: (S5) Where the assumed field propagation along direction (S6) Under the rotating wave approximation, we obtain: (S7) Therefore, the complete Hamiltonian is: (S8) The unitary transformation of a single atom is defined as: (S9) The global unitary transform is defined as: (S10) Therefore, the state ket is transformed into .here and It is the laser frequency of pump fields I and II, and and It corresponds to the input signal photon and output telecommunication photons The frequency of the Hamiltonian. The Hamiltonian transformation is... (S11) Therefore, the complete Hamiltonian in the rotating frame takes the following form (S12) The assumption is that energy is conserved. Phase matching conditions Detuning is defined as... and .

[0168] The atomic collective excitation operator is introduced and defined as: (S13) We assume the system is in a weakly excited region, and that the atomic states are always within a symmetric collective excited manifold. This is a reasonable assumption for atomic states 3 and 4, since the input at 780 nm is at the minority photon level. This is also a reasonable assumption for state 2 due to the decay channels of other hyperfine ground states outside the four-wave mixing loop. Under this low-excitation assumption, The operators approximately obey the commutative relations of boson annihilation and creation operators. In this symmetric manifold, this can be written as: (S14) Hamiltonian is (S15) The Heisenberg-Langev equation is: (S16) The input noise term is set, namely In one embodiment, the system is configured to detune pump II. Then through settings Finding a steady state is reasonable. Therefore, we have: (S17) Deleting small nonlinear terms will result in: (S18) Therefore, all nonlinearities can be eliminated by substitution. Terms that make the matrix form of the equation: (S19) The Fourier transform of the operator in the rotating frame is defined as: (S20) Therefore, in frequency space, the above matrix equation becomes (S21) Solving the linear equation yields: (S22) in (S23) In input-output formalism, the input-output relationship is... (twenty four) In the conversion system, only 780 nm is used as the mode. Input, making And the input-output relationship becomes: (S25) Further definition (S26) Make (S27) The photon flux operator is calculated as follows: From this, the average photon flux of the output 1324 nm signal can be obtained. By definition: (S28) in Understanding as future time Field operator outside the cavity .

[0169] (S29) in Interpreted as the field operator outside the cavity at t=0 Comparing the definition and operator Fourier transform, we have (S30) However, the annihilation and creation operators are used in the normal order. This is because they always appear in conjugate pairs. (S31) Furthermore, according to the definition of Fourier transform, (S32) Therefore, this can be written as: (S33) LHS is the time The average photon flux at that location. To find the conversion efficiency, in one case, note that... The contribution comes only from frequencies near the center. Therefore, a narrow bandwidth approximation can be performed: (S34) Therefore, the conversion efficiency is In the weakly excited region, the conversion efficiency is independent of the number of input photons. In one implementation configuration, ,and In the limit of free-space coupling, i.e., a very wide cavity (large... Heda The conversion efficiency can be approximated as: (S35) HOM Interference Model Return to reference Figures 10A-10B Two independent coherent beams are incident on input ports a and b of a standard (i.e., ideal 50:50, unpolarized) beam splitter 1012; the system calculates at the two output ports c and d (e.g., at...). Figure 10B The middle port c is Charlie, and in Figure 10B The overlap rate observed at port d (where d is the overlap rate observed at two specific measurement times) is used as a reference. and A function. One objective is to calculate the shape of this overlap rate relative to the time difference of arrival. What would it look like? In the case of continuous beams, this would show a decrease in HOM interference. Then, the case where the beam is pulsed in a timely manner is considered.

[0170] Initial bundle state In this embodiment, the incident beams each originate from a laser with a small but limited linewidth range. Then, it is assumed that each individual mode within the beam... In coherent state ,in: (S36) In a finite quantization volume Represented as corresponding to a single pattern By making the quantization volume infinite and using symbols... This definition can be further extended to continuous frequency space. If It is assigned to describe the corresponding spectral functions of the beam entering at port a and the beam entering at port b. ,like Figure 10B As shown, the fully entered state can be written as: (S37) Intensity, Transformation, and Coherence Time: Weiner-Khinchin Interlude According to the general Glauber's theory of optical detection, at any given time Having state The intensity of any beam in the field can be written as: (S38) here It is a positive frequency electric field operator: (S39) Apply it to state The bundle: (S40) Then define The Fourier transform of the expression is represented as: : And therefore (S41) Also Figures 10A-10B Channel a (e.g., Figure 10B The Alice channel in the image is shown. Equation S41 is used to define the convention for the inverse Fourier transform, that is, from frequency to time, and then the forward transform is... (S42) Therefore, these two are called a Fourier transform pair, denoted as: (S43) Use the notation for autocorrelated outputs: (S44) For rate and coincidence distribution exist Figures 10A-10B In another view, the spectral function is now described. The input beam at point A has a transformation Furthermore, the input beam at point B has a spectral function. and the corresponding transformation After writing to the output state, the system calculates the rate of the observed pair at the output, and then considers the cases of continuous beam and envelope pulse beam.

[0171] For the input of the 50:50 symmetrical beam splitter, by Given a coherent input state, the two output states are... It can be seen that this evolution conserves energy when the two beams inherit the phase relationship between the same modes in the original beam. For two input beams, the system can simply add their amplitudes at the two outputs, remembering that one of them must be out of phase (this is necessary to conserve energy, and is therefore a general property of beam splitters). The states and transformations of the output beams at port positions c and d are as follows: (S45) At point c and at d (S46) Therefore, at ports c and d, especially in time... and The two-photon observation rate at that location can be written as: (S47) Substituting equations S39 and S45 into the above, we get... (S48) Extended equation S48 gives three types of terms: Balanced and synchronized terms, containing only products. and / or The combination of these terms evaluates both pairing factors simultaneously. These terms are direct real numbers corresponding to the product of beam intensities, as described below; Balanced and asynchronous terms are included in calculations performed at different times. and Product. These terms are where the interference effect occurs; Unbalanced terms, where at least one factor of or son They are not balanced by their complex conjugates. These terms will have a very rapidly changing phase at all times and will vanish in any time integral, for example, when performed in equation S51 below.

[0172] If the unbalanced terms are discarded, equation S48 can be rearranged as follows: (S49) The single-photon intensities of the two incident beams are labeled as follows: and .

[0173] For the experiment, the system integrates the number of pairs observed over time and groups them according to the time difference between detections. Therefore, the data from... The variable was changed Then for all Integrate the pairing rate on: (S50) (S51) It can be recognized that the integral of each product term in equation S51 has an autocorrelated or cross-correlated form. Then, by exchanging the integrals... The order of operations simplifies it to a compact form with only two autocorrelation pairs: (S52) In the form of equation S52: the first combination term comes only from the power envelope of the bundle, but the second interference term has not yet been connected to the measurable characteristics of the individual bundles. To make further progress, more of these properties need to be specified. The case of CW bundles is described next, followed by the more general case of envelope pulse bundles.

[0174] Interference tilt angle under continuous wave conditions Starting with the CW case, we assume the frequency spread of the beams is relatively small and their spectral distribution is smooth. In this case, the intensity... It will be constant, and the pairing rate vs. The only structure in the equation will come from the interference terms. The only physical parameter defining the two beams is their line shape: for narrowband beams, the different frequency components will be out of phase with each other, making the sum and phase at any given time practically random. Therefore, it is expected that the interference terms can be expressed purely from the spectral density function or line shape function of the two beams, which are known to be... and .

[0175] First, use and Instead and To recast the interference terms. Focusing only on equation S52. Regarding the operator's argument, after a certain presupposition, we can derive: (S53) in and (S54) The core of equation S53 can be rewritten as (S55) Because of the expected phase function and As The function changes very quickly and almost randomly; essentially, it changes on the order of the inverse of the quantization time. This will introduce new and irrelevant values ​​to the phase. Therefore, it can be seen that the integral of equation S55 will contribute almost nothing due to the rapidly and randomly shifting complex phase, except along its path. Furthermore, the phase difference disappears and the integral is a straight line that is entirely real. This then allows us to use... and The delta function between them effectively replaces the phase exponential factor: (S56) With this, equation S56 can be substituted into equation S53, and then substituted into equation S52, to finally obtain the relationship between rate and time difference as follows: (S57) Gaussian beam shape.

[0176] Use the following symbols: (S58) Here we continue the convention of using uppercase variables for time functions and lowercase variables for frequency functions. Note that the function defined in equation S58 is not area-normalized, but rather fixed at... and It has a maximum value of 1.

[0177] First, for cross-correlation, we have: (S59) The standard symbol " "Used for product sum" Apply this convention to time. and frequency The transformations between them, as arranged in equations S41 and S42, yield the following: (S60) in .

[0178] Regarding the CW situation and Since it is a constant, the autocorrelation in the first term of equation S57 simplifies to a product, leaving: (S61) Assuming the two bundles have the same linewidth However, it may have a slightly different center frequency. and The intensity distribution of the beam at points a and b can then be written as: and (S62) Substituting these into equation S61, we get: (S63) For the relationship between rate and The relationship. If this rate is normalized to a large... The platform value at that time can then be used to determine visibility. To derive its expression, we can achieve the following: ,in (S64) Pulse beam situation The pulse beam is simulated by taking the electric field function of the CW beam and modulating it with the pulse profile function.

[0179] The two "mother" CW beams are first used with electric field functions and This indicates that it has the same characteristics as those used in general CW situations. and The same properties, and especially as described in equation S54. The convention of using uppercase for time functions and corresponding lowercase for frequency functions continues. and (S65) And then and (S66) in and It is rapidly changing and relatively random. function.

[0180] Now we define two pulse envelope amplitude functions for the two beams. and Thus, the complete electric field function at both input terminals is obtained: (S67) (S68) Note that even for a given CW bundle and This will produce the given information in formula S68. and pulse envelope function and It's not the only one, but it can be... It has an arbitrary phase structure. Assume... and They have a constant phase; therefore, without losing generality, they can be considered as having a constant phase. The range of real and positive numbers, consistent with the beam splitter model. With this and starting from equation S53, we get: (S69) Equation S69 is completely universal so far. However, it utilizes... and as well as The cross-correlation property, because they are narrowband continuous bundles, because they are in It has a random phase. Following the logic from equation S55 to equation S56, now based on equation S66, equation S69 can be simplified in two steps to: (S70) Substituting the rate back into the main equation S52, we get: (S71) As a generalized version of Equation S57, it is now used for pulsed beams. Equation S71 is now fully operational, involving only three well-defined real-valued functions: the spectral shapes of the two parent CW beams. and and the product of the two pulse envelope amplitude functions .

[0181] Single, synchronous, symmetrical pulse First, consider the single-envelope case, where (i) each beam envelope contains only one well-shaped pulse; (ii) both pulses arrive at the beam splitter simultaneously; and (iii) the pulse shapes are symmetrical about their peak values. This allows us to conveniently... Set as and The peak arrival time. In this case, the product transform... It will be a real number, and about It is symmetrical, and cross-correlation will be easy.

[0182] It is also assumed that the mother beam shape and pulse amplitude shape are Gaussian. For further simplification, the mother beam is assigned power levels... and And assume at the pulse peak Then, according to equation S62, set... (S72) (S73) (S74) In this context, it is assumed that the two parent beam shapes have the same Gaussian frequency standard deviation. And the two pulses have the same time standard deviation. And allow center frequencies between mother bundles. There are minor differences, but they ensure complete synchronization of the two pulses. Note that the selection convention is... Describing intensity The Gaussian width of the pulse, therefore amplitude modulation and Gaussian width is large times.

[0183] First, evaluate the classical terms from equation S71: (S75) In simple cases, the interference term is also straightforward; firstly, regarding the pulse shape factor: And for the mother CW bundle width factor: (S76) Substituting into equation S71, performing the final cross-correlation and inverse Fourier transform, and taking the real part, we obtain the total interference term: (S77) Adding the two terms from equations S75 and S77, and after some simplification, the pairwise velocity in the case of Gaussian beams and pulses can be written as: (S78) in visibility It is defined by the exact same relative intensity as Equation S64, and reaches a maximum value of 0.5 when the peak intensity of the bundles is equal.

[0184] Equation S78 is now the complete form for the rate pair in the case of a single synchronous Gaussian pulse, with only four shape parameters: pulse width, mother beam linewidth, mother beam frequency offset, and... HOM visibility at the location. Its behavior under two natural limits can be quickly examined, namely very wide pulses and very narrow pulses.

[0185] exist Under the largest limit, the first Gaussian in equation S78 is The nearest neighbor has a constant value of 1. Meanwhile, the standard deviation of the second Gaussian beam will approach... Therefore, equation S78 will be simplified as expected to the CW case result of equation S64.

[0186] exist In small limits, especially with Compared to the smaller one, the second Gaussian σ will be close to That is, σ is the same as that of the first Gaussian. Removing common Gaussians yields: (S79) Therefore, in the short pulse limit, i.e., much shorter than the coherence time of the mother beam, there exists an extremely simple result: if the frequency mismatch... Sufficiently small to keep the cosine factor constant, HOM interference has the ability to... Peak height reduction factor in the distribution at location The effect is the same, but the shape remains the same.

[0187] This extends to a series of separate, synchronized, symmetrical pulses.

[0188] In the experiment, not only a single pulse was generated at each input, but also a pulse train. The above analysis can be extended to pulse train input bundles, provided that the pulses are well separated. Two assumptions are made: 1) Each pulse ends at the beginning of the next pulse; for example, at any given time, only one pulse in the sequence can have a non-negligible intensity; 2) The interval between pulses is greater than the width of the pulse itself. It's very long.

[0189] Qualitatively speaking, if the pulses in the sequence are well separated, as described above, and the pulses in one input channel always arrive at the beam splitter in sync with the pulses in another channel, then the experiment can be considered as repeated at intervals with single-pulse versions. For the distribution... The analysis of the nearby "central" peak is exactly the same as in the single-pulse case. The only change in the distribution is the appearance of a larger peak. Yes, stay away This corresponds to the arrival of photon pairs from asynchronous pulses. In the case of such well-separated pulses, the "differentiated" pairs will not exhibit any detectable quantum interference effects: only the central pair peaks show an effect, which is the same as the effect in the case of a single pulse.

[0190] With this, the result of the regular synchronous Gaussian pulse train can be written to the input channel. All that's needed is to copy equation S78 and space it with... Classical terms with interval repetition: (S80) The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of instructions comprising one or more executable instructions for implementing a specified logical function. In some alternative embodiments, the functions mentioned in the blocks may not occur in the order shown in the drawings. For example, two blocks shown consecutively may actually be implemented substantially simultaneously, or these blocks may sometimes be implemented in reverse order, depending on the functions involved. It will also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented by a dedicated hardware-based system that performs the specified function or action or executes a combination of dedicated hardware and computer instructions.

[0191] While this disclosure has been specifically shown and described with respect to preferred embodiments thereof, those skilled in the art will understand that foregoing and other changes in form and detail may be made without departing from the spirit and scope of this disclosure. Therefore, it is intended that this disclosure be limited to the exact form and detail described and shown, but falls within the scope of the appended claims.

Claims

1. A system for performing operations on a quantum network, comprising: Quantum manipulation elements, which are configured to directly manipulate and transmit quantum information; A central controller is configured to synchronize and orchestrate the operation of the quantum manipulation element toward orchestrated actions, which at least include generating entangled photons, quantum memory operations, and quantum measurements. and A controllable instrument configured to interface with and drive the quantum manipulation element, the controllable instrument converting control commands from the central controller into operating parameters of the quantum manipulation element, and the controllable instrument further configured to provide feedback from the quantum measurement to the central controller.

2. The system according to claim 1, wherein, The controllable instrument is functionally grouped into subsystems and settings, and also includes a clock interface for distributing timing information to the subsystems and settings.

3. The system according to claim 2, wherein, The clock interface further facilitates subsynchronous resolution for coherent manipulation of quantum information.

4. The system according to claim 1, wherein, The controllable instrument is also configured to perform compensation between distance connections to maintain coherence between different nodes over relevant time scales.

5. The system according to claim 1, wherein, The controllable instrument includes at least a signal generator, a time marker, and an oscilloscope.

6. The system according to claim 1, wherein, The quantum manipulation element includes at least atoms, optical fibers, optical components, and photodetectors.

7. The system according to claim 1, wherein, The central controller is also configured to manage the quantum information, use models learned from data acquired from the quantum measurements to understand the quantum network, and use the learned understanding to verify the quantum network.

8. The system of claim 1 further includes a first set of application programming interfaces, the first set of application programming interfaces being used to interface the central controller with the controllable instrument interface, wherein one or more of the first set of application programming interfaces are used to transmit control commands from the central controller.

9. The system according to claim 8, wherein, The first set of application programming interfaces operates independently of the brand and model of the controllable instrument.

10. The system of claim 1, further comprising a second set of application programming interfaces for interfacing the central controller with one or more user-defined quantum network application interfaces.

11. The system according to claim 10, wherein, The user-defined quantum network applications include at least distributed quantum gate operations, teleportation-based services, HOM indistinguishability verification, and entanglement swapping.

12. A method for operating a quantum network, comprising: Configure quantum manipulation elements to directly manipulate and transmit quantum information; A central controller is configured to synchronize and orchestrate the operation of the quantum manipulation elements toward orchestrated actions, which at least include generating entangled photons, quantum memory operations, and quantum measurements. and A controllable instrument is configured to interface with and drive the quantum manipulation element. The controllable instrument translates control commands from the central controller into operating parameters for the quantum manipulation element. The controllable instrument is also configured to provide feedback from the quantum measurement to the central controller. The quantum network operates via a hierarchy that interfaces the quantum manipulation elements with the controllable instruments and the controllable instruments with the central controller.

13. A method for quantum frequency conversion, the method comprising: Receive a first signal encoded with a quantum bit, wherein the first signal has a first frequency; Receive at least one laser beam; Configure the at least one laser beam to generate at least one control beam; The first signal is combined with the at least one control beam to generate a second signal encoding the qubit, wherein the second signal has a second frequency; and The second signal is stored in a quantum memory device.

14. The method of claim 13, wherein: The at least one laser beam includes a first laser beam having a third frequency and a second laser beam having a fourth frequency; Configuring the at least one laser beam includes configuring the first beam to generate a first control beam and configuring the second beam to generate a second control beam; and Combining the first signal with the at least one control bundle includes combining the first signal with the first control bundle and the second control bundle to generate the second signal.

15. The method of claim 14, wherein: The first frequency is 780 nanometers (nm); The second frequency is 1324 nm; The third frequency is 795 nm; and The fourth frequency is 1367 nm.

16. The method of claim 14, wherein: Configuring the first beam to generate the first control beam includes modulating the first beam; and Configuring the second beam to generate the second control beam includes frequency locking of the second beam.

17. The method of claim 13, further comprising: Attenuating the first signal involves using an electro-optic modulator (EOM) to create a field envelope for the first signal.

18. The method according to claim 17, wherein, Frequency locking of the second beam includes: Operating an indium gallium arsenide (InGaAs) balanced amplification photodetector to obtain an optical-optical double resonance (OODR) spectrum; Scan the second beam while keeping the first signal frequency locked; An error signal is generated by modulating the second beam at a predetermined frequency; and The proportional-integral-derivative (PID) controller is operated to lock the second beam according to the error signal.

19. The method according to claim 13, wherein, Combining the first signal with the at least one control beam includes: The first state of the diamond energy level structure is resonantly coupled to the third excited state of the diamond energy level structure, wherein the diamond energy level structure comprises: As the first state of the ground state; The second state is an excited state with higher energy than the first state; The third high state is an excited state with higher energy than the second state; The fourth state is an excited state with a higher energy than the third state, wherein the input quantum field that receives the first signal is connected by the first state and the third state of the diamond energy level structure, and the output quantum field that outputs the second signal is connected by the second state and the fourth state of the diamond energy level structure. Couple the first state to the second state; and The third state of the diamond energy level structure is coupled to the fourth state.

20. The method of claim 13, further comprising filtering out the at least one control bundle to obtain the second signal.

21. The method according to claim 20, wherein, Filtering out the at least one control beam includes using a Glan laser (GL) polarizer and at least one wavelength filter.

22. The method according to claim 13, wherein, The quantum memory device is a room temperature vapor chamber.

23. A system comprising: Combined optical equipment, which is configured as follows: Generate a first signal that encodes a quantum bit, wherein the first signal has a first frequency; Generate at least one laser beam; At least one control beam is generated based on the at least one laser beam; Frequency conversion device, which is configured to: The first signal is combined with the at least one control beam to generate a second signal encoding the qubit, wherein the second signal has a second frequency; and The second signal is stored in a quantum memory device.

24. The system according to claim 23, wherein, The combined optical device includes: A first laser pump field, configured to generate the first signal; and At least one additional laser pump field, the at least one additional laser pump field being configured to generate the at least one laser beam.

25. The system according to claim 24, wherein: The at least one laser beam includes a first laser beam having a third frequency and a second laser beam having a fourth frequency; The at least one additional laser pumping field includes: A second laser pump field, configured to generate the first laser beam; and A third laser pump field is configured to generate the second laser beam.

26. The system according to claim 25, wherein: The combined optical device is configured to: Configure the first beam to generate the first control beam; Configure the second beam to generate the second control beam; and The frequency conversion device is configured to combine the first signal with the first control beam and the second control beam to generate the second signal.

27. The system according to claim 25, wherein: The first frequency is 780 nanometers (nm); The second frequency is 1324 nm; The third frequency is 795 nm; and The fourth frequency is 1367 nm.

28. The system according to claim 25, wherein, The combined optical device is configured to: The first beam is configured to generate the first control beam by modulating the first beam; and The second beam is configured to generate the second control beam by frequency locking of the second beam.

29. The system according to claim 23, wherein, The combined optical device is configured to use an electro-optic modulator (EOM) to attenuate the first signal to create a field envelope of the first signal.

30. The system of claim 28, wherein, for frequency locking of the second beam, the combined optical device is configured to: Operating an indium gallium arsenide (InGaAs) balanced amplification photodetector to obtain an optical-optical double resonance (OODR) spectrum; Scan the second beam while keeping the first signal frequency locked; An error signal is generated by modulating the second beam at a predetermined frequency; and The proportional-integral-derivative (PID) controller is operated to lock the second beam according to the error signal.

31. The system according to claim 23, wherein, In order to combine the first signal with the at least one control beam, the frequency conversion device is configured to: The first state of the diamond energy level structure is resonantly coupled to the third excited state of the diamond energy level structure, wherein the diamond energy level structure comprises: As the first state of the ground state; The second state is an excited state with higher energy than the first state; The third high state is an excited state with higher energy than the second state; The fourth state is an excited state with a higher energy than the third state, wherein the input quantum field that receives the first signal is connected by the first state and the third state of the diamond energy level structure, and the output quantum field that outputs the second signal is connected by the second state and the fourth state of the diamond energy level structure. Couple the first state to the second state; and The third state of the diamond energy level structure is coupled to the fourth state.

32. The system according to claim 23, wherein, The frequency conversion device is configured to filter out the at least one control beam to obtain the second signal.

33. The system according to claim 32, wherein, The frequency conversion device includes a GL laser polarizer and at least one wavelength filter configured to filter out the at least one control beam.

34. The system according to claim 23, wherein, The quantum memory device is a room temperature vapor chamber.

35. A method for determining the indistinguishability among qubits, the method comprising: Receive the first packet of photons from the first quantum memory; Receive the second packet of photons from the second quantum memory; Determine the first arrival time of the first packet of photons; Determine the second arrival time of the second packet of the photon; Determine the difference between the first arrival time and the second arrival time; Determine the overlap rate between the first packet and the second packet of photons; and HOM visibility is determined based on the overlap rate and the difference between the first arrival time and the second arrival time, wherein the HOM visibility indicates the indistinguishability between the first packet and the second packet of photons.

36. The method of claim 35, wherein: The first packet of photons received from the first quantum memory via a first optical path having a first distance; and The second packet of photons is received from the second quantum memory via a second optical path having a second distance different from the first distance.

37. The method of claim 35, further comprising: The polarization of the first packet of photons is compensated; and The polarization of the second packet of the photon is compensated.

38. The method according to claim 35, wherein, The difference between the average number of photons in the first packet of photons and the average number of photons in the second packet of photons is within a predetermined threshold that maximizes the visibility of the HOM.

39. The method according to claim 38, wherein, The average number of photons in the first packet and the average number of photons in the second packet are defined within a pulse time envelope.

40. The method of claim 35, wherein: The first packet and the second packet of photons are received by the HOM detection system; and The HOM detection system, the first quantum memory, and the second quantum memory are located in the same location.

41. The method of claim 40, wherein, The identical location, including the first quantum memory, the second quantum memory, and the HOM detection system, is the first location, and the method further includes: The first packet of photons is received by the first quantum memory from a first light source located at a second position different from the first position; and The second packet of photons is received by the second quantum memory from a second light source located at a third position that is different from the first position and different from the second position.

42. The method of claim 35, further comprising: Multiple optical elements are used to compensate for the polarization of the first packet of photons and the polarization of the second packet of photons in order to guide macroscopic light to a polarimeter for measurement; and The plurality of optical elements are automatically removed to release the first packet and the second packet of photons into the HOM detection system.

43. The method according to claim 35, wherein, Determining the overlap rate includes: It is determined that the first arrival time falls within the time period; Determine the second arrival time within the time period; and In response to determining the first and second arrival times within the time period, an overlap count is recorded.

44. The method of claim 43, wherein: The first arrival time is a photon detection event in the first photon detection event set in the first channel of the first packet that received the photon; The second arrival time is a photon detection event within the set of second photon detection events in the second channel of the second packet that received the photon; and The overlap count is within the number of overlap counts.

45. The method according to claim 44, wherein, The number of overlaps is the first number of overlaps: Add a delay to at least one of the first channel and the second channel; The added delay is used to monitor the first set of photon detection events in the first channel and the second set of photon detection events in the second channel; A second number of overlap counts is determined based on monitoring using the added delay; and Determine the relationship between the first number of overlapping counts and the second number of overlapping counts.

46. ​​The method of claim 45, further comprising adjusting the delay to minimize the overlap rate based on the relationship between the first number of overlap counts and the second number of overlap counts, wherein minimizing the overlap rate maximizes the HOM visibility and the indistinguishability.

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