TCEP Based Synchronisation for Practical Communication Network

Distributed quantum computing has been well-known for many years as a system composed of a number of small-capacity quantum circuits. Limitations in the capacity of monolithic quantum computing systems can be overcome by using distributed quantum systems which communicate with each other through known communication links. In our previous study, an algorithm with an exponential complexity was proposed to optimize the number of qubit teleportations required for the communications between two partitions of a distributed quantum circuit (DQC). In this work, a genetic algorithm is used to solve the optimization problem in a more efficient way. The results are compared with the previous study and we show that our approach works almost the same with a remarkable speed-up. Moreover, the comparison of the proposed approach based on GA with a random search over the search space verifies the effectiveness of GA.

The Quantum Internet (QI) is a hypothetical global network infrastructure that exploits quantum mechanics principles to distribute qubits worldwide. The QI will enable breakthrough applications like unconditional security, distributed quantum computing, and quantum metrology. Nonetheless, the QI is currently a research-stage technology with daunting challenges until fully-functional quantum networks (QNs) can be realized. QNs are not standalone but require classical networks to assist the qubits exchange between remote places through quantum teleportation. On the other hand, QNs control and management planes will remain classical due to quantum networking technology manufacturing complexity and cost. This article addresses integrating QNs with Sixth Generation and Beyond (6GB) mobile networks. Sixth Generation and Beyond (6GB) are the foreseen next generations of wireless networks, offering extensive ubiquity and improved ultra-reliable low-latency support over larger distances than their predecessors. Therefore, it is the best-suited candidate to enable potential mobile and non-terrestrial quantum applications. Unlike existing literature highlighting quantum technology’s potential benefits to mobile networks, this work presents a fresh vision in which 6GB enhances the QI and even contributes to accelerating its development. To that end, we identify target QNs scenarios enabled, facilitated, or benefited by 6GB. We propose a Software-Defined programmable 6GB-integrated QN architecture with slicing support and the associated procedure to create virtual QNs or slices. Last, we present a proof-of-principle showing that QNs can impose deterministic low-latency requirements out of 5G reach.

The IEEE 1588 Precision Time Protocol (PTP) has emerged as a critical standard for achieving highly accurate time synchronization across distributed systems, particularly where precision and low latency are essential. Widely applied in domains such as industrial automation, telecommunications, power grid management, nuclear fusion, and scientific facilities. PTP facilitates synchronized operations and enhances control reliability across networked devices. Utilizing the versatility, real-time processing capabilities, and hardware timestamping of field-programmable gate arrays (FPGAs), recent implementations of PTP on FPGA platforms have brought forth advancements in time synchronization precision, flexibility, and integration with complex systems. FPGAs offer significant advantages in implementing PTP, including customizable hardware acceleration, low latency, and compatibility with high-performance interfaces, which enable precise, scalable, and cost-effective solutions for time-critical applications. This paper presents a comprehensive review of FPGA-based PTP implementations, examining the selection of FPGA platforms, design of Intellectual Property (IP) cores, and evaluation of application-specific performance metrics. By synthesizing recent research, we outline the advancements, challenges, and future directions for FPGA-based PTP solutions, with an emphasis on addressing the needs of modern distributed control and data acquisition systems.

Inspired by the recent developments in the fields of quantum distributed computing, quantum systems are analyzed as networks of quantum nodes to reduce the complexity of the analysis. This gives rise to the distributed quantum consensus algorithms. Focus of this paper is on optimizing the convergence rate of the continuous time quantum consensus algorithm over a quantum network with $N$ qudits. It is shown that the optimal convergence rate is independent of the value of $d$ in qudits. First by classifying the induced graphs as the Schreier graphs, they are categorized in terms of the partitions of integer $N$. Then establishing the intertwining relation between one level dominant partitions in the Hasse Diagram of integer $N$, it is proved that the spectrum of the induced graph corresponding to the dominant partition is included in that of the less dominant partition. Based on this result, the proof of the Aldous' conjecture is extended to all possible induced graphs and the original optimization problem is reduced to optimizing spectral gap of the smallest induced graph. By providing the analytical solution to semidefinite programming formulation of the obtained problem, closed-form expressions for the optimal results are provided for a wide range of topologies.

With their ability to process and transfer quantum information, large-scale entanglement-based quantum networks could be at the heart of a new age of quantum information, enabling fundamentally new applications such as distributed quantum computation, quantum communication, and quantum enhanced sensing. Due to their long spin coherence, controllable local qubit registers and optically active spins, color centers in diamond are prime candidates for nodes of such a network, and have enabled some of the most advanced quantum network demonstrations to date. These demonstrations include the distribution of a 3-node GHZ state across a quantum network, entanglement swapping, entanglement distillation, and memory-enhanced quantum communication. To move beyond current proof-of-principle networks, a further increase of entanglement generation rates is crucial. This thesis presents theoretical and experimental work on enhancing the spin-photon interface of color centers in diamond to achieve this goal, making use of the Purcell effect. The discussed work follows two main directions: embedding of color centers in open, tuneable Fabry-Perot micro-cavities, and in all-diamond photonic crystal cavities. First, we describe theoretical and experimental progress towards cavity-enhanced quantum networks based on nitrogen-vacancy (NV) centers in diamond. Due to their first order sensitivity to electric fields, we choose to embed NV centers in microns-thin diamond membranes that can be integrated into open fiber-based micro-cavities. We develop analytical methods to optimize the design of such open cavity systems for maximum Purcell enhancement of embedded color centers. We demonstrate a method to fabricate optically coherent NV centers in microns-thin diamond membranes, and use such structures to demonstrate the resonant excitation and detection of coherent, Purcell enhanced NV emission. A theoretical model in excellent agreement with our results suggests our system can improve entanglement rates between distant NV centers by two orders of magnitude with near-term improvements to the setup. Second, we describe progress towards an efficient spin-photon interface of group-IV color centers in diamond by coupling them to photonic nanostructures, allowing for large-scale integration. Due to their first-order insensitivity to electric fields, group-IV color centers can be brought in close proximity to surfaces (~ 100 nm), allowing for sub-wavelength mode volumes and thus very high Purcell factors. We numerically optimize photonic crystal cavity designs to maximize the Purcell enhancement of embedded emitters, test the robustness of our designs to real-world fabrication imperfections, and devise a method to efficiently interface nanophotonic structures. We then proceed to fabricate all-diamond photonic crystal cavities, making use of a dry etching technique that is selective to different crystallographic directions, and characterize the resulting optical quality factors. Finally, we marry the developed fabrication methods to fabricate microns-sized diamond platelets that can be transferred from a holding frame in a controlled fashion. This capability could be crucial for the realization of hybrid photonic circuits that we expect to be at the heart of future large-scale quantum networks.

Quantum networks based on solid-state spin defects present a transformative approach to secure communication and distributed quantum computing, utilizing quantum entanglement and coherent spin–photon interfaces. Silicon carbide (SiC) stands out as a compelling material platform due to its unique combination of a wide bandgap, high optical nonlinearity, CMOS-compatible fabrication, and controllable spin-active defects. These intrinsic properties facilitate efficient photon emission, robust spin coherence at both room and cryogenic temperatures, and integration with photonic nanostructures. Recent advancements in defect engineering and micro-nanophotonics have unlocked the potential of SiC quantum nodes, which feature electron-nuclear spin systems for high-fidelity quantum operations and long-lived quantum memories. Key steps such as single-shot readout and spin-photon entanglement have been successfully demonstrated, bringing SiC closer to a real quantum network platform. This review offers a comprehensive overview of the advancements in SiC-based quantum networks, encompassing key aspects such as defect fabrication methodologies, optimization of spin-photon interfaces, and strategies for photonic integration. Additionally, it examines the existing challenges and outlines promising future directions in this rapidly evolving field.

Charged quantum dots containing an electron or hole spin are bright solid-state qubits suitable for quantum networks and distributed quantum computing. Incorporating such quantum dot spin into a photonic crystal cavity creates a strong spin-photon interface in which the spin can control a photon by modulating the cavity reflection coefficient. However, previous demonstrations of such spin-photon interfaces have relied on quantum dots that are charged randomly by nearby impurities, leading to instability in the charge state, which causes poor contrast in the cavity reflectivity. Here we demonstrate a strong spin-photon interface using a quantum dot that is charged deterministically with a diode structure. By incorporating this actively charged quantum dot in a photonic crystal cavity, we achieve strong coupling between the cavity mode and the negatively charged state of the dot. Furthermore, by initializing the spin through optical pumping, we show strong spin-dependent modulation of the cavity reflectivity, corresponding to a cooperativity of 12. This spin-dependent reflectivity is important for mediating entanglement between spins using photons, as well as generating strong photon-photon interactions for applications in quantum networking and distributed quantum computing.

A study of the use of digital techniques for the real-time, fast neutron coincidence analysis of time- and space-correlated radiations emitted by californium-252 and uranium-235 is described. These radiations have been measured with detectors based on the organic liquid scintillant, EJ-309. Time-synchronized neutron and gamma-ray event-trains, separated with pulse shape discrimination, have been sampled with a field-programmable gate array programmed with an algorithm developed in this research. This approach has been used to extract the interval time distribution of this event-train, with a time resolution of 5 ns, to investigate the temporal correlation between the neutrons and/or gamma rays emitted in the spontaneous fission of californium-252. The established model for the characterization of the interval-time distributions of correlated thermal neutron events, used widely in thermal neutron coincidence assay, has been extended to fast neutrons. The influence of geometry and the surroundings on these distributions has been investigated and quantified: the temporal coefficients for the die-away of the distributions for neutrons and gamma rays are 3.18\pm0.09 ns and 1.49\pm0.06 ns, respectively. It has been observed that 99.7% of the correlated neutrons and gamma rays are detected within 27 ns and 21 ns of each other, respectively, when a low-scatter geometry is examined. The spatial distribution of fast neutrons emitted in spontaneous fission (californium-252) has also been investigated to yield the evidence for the angular distribution of higher-order, correlated neutrons presented in this thesis; this infers a dipolar trend for third (triplet) and fourth (quadruplet) neutrons consistent with that known for second (doublet) neutrons. The gamma-ray emission has been used to provide time-of-flight information and hence the neutron spectrum for fission neutrons from californium-252. A technique for the determination of the foreground and background coincidence distribution of the emitted fast neutrons and/or gamma rays for passive and active neutron coincidence counting methods has been developed. Finally, two models have been developed to correct for erroneous coincidence events which might otherwise limit the use of organic scintillators in coincident assay: one for photon breakthrough and one for detector crosstalk. These models have been validated using californium-252 indicating that photon-breakthrough constitutes a 20% increase in the neutron count rates whilst crosstalk can result in increases of 10% and 35% on first-and second-order coincident events, respectively, for the investigated geometries. The instrumentation, techniques and results reported in this thesis extend our understanding of the fundamental temporal characteristics of nuclear fission, and are of direct relevance to the application of organic scintillators with pulse shape discrimination to nuclear safeguards and non-proliferation verification.

A high-performance framework for a network programmable packet processor using P4 and FPGA

Packet classification is one of the most important functions in the router design. This is to support a variety of network functionalities. Pipeline-based decision tree is one of the best choices for increasing throughput on packet classification. SRAM-based and hardware-based solutions are often used to develop a high speed packet classification engine. However, SRAM-based solutions suffer from throughput degradation, delay variation and memory overflow. Moreover, hardware-based solutions suffer from fast update and non-linear structure. To address these problems, we propose a FPGA-based multipipeline architecture for 5-tuple rules into multiple subsets to build a decision tree with high throughput and fast update. To fit the current largest rule set in the FPGA device, we propose several optimization techniques, so that maximize the resource utilization while sustaining high throughput. In this architecture Look Up Tables (LUTs) are used instead of memory blocks. Partial reconfiguration in Field Programmable Gate Array (FPGA) used to reduce the time that is needed to change the behavior of architecture. The implementation results show that our architecture can store over 10K real-life rules in LUTs of a single Xilinx Virtex-6 FPGA, and sustain over 120 Gbps (i.e. 3× OC-768 rate) throughput for minimum size (40 Bytes) packets.

Quantum network extends the ability to transmit information securely from two-party communication to multi-party communication with arbitrarily long distances. The efficiency of secure communication in a quantum network depends on both the topology of the network and the strategy of communication relays. In this paper, we propose a strategy to build a quantum network integrating various types of quantum secure direct communication (QSDC) schemes. A cost optimization model is presented to measure the cost of transmitting secure messages in a quantum network. Within the model, two types of quantum network strategies, the quantum circuit switching strategy and the quantum packet switching strategy, are proposed and compared. Numerical simulations in a specific network show that the quantum packet switching strategy is more favorable in future quantum networks taking into account robustness and cost required when using different types of QSDC schemes.

Matter-light quantum interface and quantum memory for light are important ingredients of quantum information protocols, such as quantum networks, distributed quantum computation, etc. [P. Zoller et al., Eur. Phys. J. D 36, 203 (2005)]. In this paper we present a spatially multimode scheme for quantum memory for light, which we call a quantum hologram. Our approach uses a multiatom ensemble which has been shown to be efficient for a single spatial mode quantum memory. Due to the multiatom nature of the ensemble and to the optical parallelism it is capable of storing many spatial modes, a feature critical for the present proposal. A quantum hologram with the fidelity exceeding that of classical hologram will be able to store quantum features of an image, such as multimode superposition and entangled quantum states, something that a standard hologram is unable to achieve.

Entanglement swapping is a core operation in a quantum network. It consumes a pair of entanglements to build a remote entanglement between two parties without direct interaction. In a buffered quantum network, unpaired entanglements can be stored in a ...

Quantum networks interconnecting quantum processor nodes via optical fibers promise groundbreaking applications in fields like secure communication, distributed quantum computing, and enhanced quantum sensing [1]. These networks require quantum frequency conversion (QFC) to bridge the spectral gap between the optical fibers' low-absorption window near 1550 nm and the qubit platform-specific emission wavelength in the visible spectrum.

Scaling quantum computers, i.e., quantum processing units (QPUs) to enable the execution of large quantum circuits is a major challenge, especially for applications that should provide a quantum advantage over classical algorithms. One approach to scale QPUs is to connect multiple machines through quantum and classical channels to form clusters or even quantum networks. Using this paradigm, several smaller QPUs can collectively execute circuits that each would not be able on its own. However, communication between QPUs is costly as it requires generating and maintaining entanglement, and hence it should be used wisely. In this paper, we evaluate the architectures, and in particular the entanglement patterns, of variational quantum circuits in a distributed quantum computing (DQC) setting. That is, using Qiskit, we simulate the execution of an eight qubit circuit using four QPUs each with two computational and two communication qubits where non-local CX-gates are performed using the remote-CX protocol. We compare the performance of various circuits on a binary classification task where training is executed under ideal and testing under noisy conditions. The study provides initial results on suitable VQC architectures for the DQC paradigm, and indicates that a standard VQC baseline is not always the best choice, and alternative architectures that use entanglement between QPUs sparingly deliver better results under noise.