The objective of Sat-DQC is to analyze and identify potential use cases for distributed quantum computing (DQC) assisted by satellite-mediated quantum communication links. In our talk, we present our approach to analyze these scenarios: On the one hand we investigate entanglement distribution via satellites, considering, e.g., different orbits and entanglement distribution schemes. On the other hand we analyze and assess DQC applications that are suitable to be executed under the restrictions of the satellite channel, e.g. regarding entanglement distribution rate or limited connection times. One possible DQC scenario to be analyzed is connecting quantum computing clusters in different geographical locations to enable quantum computations that do not fit in any of the individual clusters. Due to the constraints on entanglement distribution via satellites, the class of DQC algorithms that can be implemented will be limited to those that generate only a small, but non-negligible, amount of entanglement across QPUs. A secondary scenario to be investigated is blind quantum computing, where a client of limited quantum resources requires to perform a calculation on a remote quantum server, without revealing any information about the computation. This scenario requires quantum communication between the two parties and, since the parties may be located far apart from each other, satellite links should be preferred.
The objective of Sat-DQC is to analyze and identify potential use cases for distributed quantum computing (DQC) assisted by satellite-mediated quantum communication links. In our talk, we present our approach to analyze these scenarios: On the one hand we investigate entanglement distribution via satellites, considering, e.g., different orbits and entanglement distribution schemes. On the other hand we analyze and assess DQC applications that are suitable to be executed under the restrictions of the satellite channel, e.g. regarding entanglement distribution rate or limited connection times. One possible DQC scenario to be analyzed is connecting quantum computing clusters in different geographical locations to enable quantum computations that do not fit in any of the individual clusters. Due to the constraints on entanglement distribution via satellites, the class of DQC algorithms that can be implemented will be limited to those that generate only a small, but non-negligible, amount of entanglement across QPUs. A secondary scenario to be investigated is blind quantum computing, where a client of limited quantum resources requires to perform a calculation on a remote quantum server, without revealing any information about the computation. This scenario requires quantum communication between the two parties and, since the parties may be located far apart from each other, satellite links should be preferred.
In future quantum networks, satellite-mediated quantum communication could be used to enable distributed quantum computing (DQC). In this talk, we present the current state of our ongoing analysis on potential use cases for satellite-enabled distributed quantum computing and on their feasibility based on hardware restrictions and algorithm requirements: On the one hand, we investigate entanglement distribution via satellites, considering different orbits and entanglement distribution schemes, and evaluating restrictions regarding, e.g., entanglement distribution rates or connection times. On the other hand, we analyse and assess possible DQC applications that might require long-range communication. Furthermore, we investigate the current state of the art of quantum-computing hardware and interconnects between matter qubits and flying qubits (photons), with a particular focus on DQC. These considerations will enable us to evaluate the gap to be bridged by future developments and to identify the necessary steps to be taken for a future implementation of satellite-enabled DQC.
The exploration of distributed quantum computing (DQC) represents a significant frontier in quantum information science, aiming to harness the unique properties of quantum mechanics to solve complex computational problems effectively. This paper discusses the diverse architectures and models that facilitate the distribution of quantum computing tasks across multiple quantum nodes, thereby addressing the limitations inherent in single quantum devices. DQC systems exploit the principles of superposition and entanglement to enhance computational capabilities beyond what classical computing systems can achieve. We examine various DQC architectures, including both quantum-classical hybrid systems and fully quantum distributed systems, highlighting their respective benefits and challenges. Key issues such as coherence, communication overhead, and error correction are discussed in detail, and we analyze specific use cases where DQC demonstrates superior performance relative to classical computing approaches, including optimization problems in logistics and finance, as well as quantum simulations for material science. Furthermore, we identify future research directions aimed at overcoming existing barriers to the practical implementation of DQC systems. By assessing the current landscape and future possibilities of DQC, this paper underscores the transformative potential of distributed quantum computing in various fields, paving the way for realizing more complex quantum algorithms and applications.
Recent developments have reported on the feasibility of interconnecting small quantum registers in a quantum information network of a few meter-scale for distributed quantum computing purposes. Small quantum processors in a network represent a promising solution to the scalability problem of manipulating more than thousands of noise-free qubits. Here, we propose and assess a satellite-enabled distributed quantum computing system at the French national scale based on existing infrastructures in Paris and Nice. We consider a system composed of both a ground and a Space segment, allowing for the distribution of end-to-end entanglement between Alice in Paris and Bob in Nice, each owning a few-qubit processor composed of trapped ions. In the context of quantum computing, this entanglement resource can be used for the teleportation of a qubit state or for gate teleportation. After having developed a model, we numerically assess the entanglement distribution rate and fidelity generated by this space-based quantum information network and discuss concrete use cases and service performance levels in the framework of distributed quantum computing. We obtain 90 end-to-end entangled photon pairs distributed over a satellite pass of 331 s that can perform a teleportation-based controlled-Z operation with a fidelity of at most 82%.
The growing demand for large-scale quantum computers is pushing research on Distributed Quantum Computing (DQC). Recent experimental efforts have demonstrated some of the building blocks for such a design. DQC systems are clusters of quantum processing units (QPUs) connected by means of quantum network infrastructures. Their extension ranges from the single box to the geographical scale. Furthermore, they can be integrated with classical High Performance Computing systems. Simulation modeling of DQC architectures provides a safe way to test and explore different what-if scenarios. Many simulation tools have been developed to support the research community in designing and evaluating quantum computer and quantum network technologies, including hardware, protocols, and applications. However, a framework for DQC simulation putting equal emphasis on computational and networking aspects has never been proposed, so far. In this paper, a design framework for DQC simulation is presented, whose core component is an Execution Manager that schedules DQC jobs for running on networked quantum computers. Two metrics are proposed for evaluating the impact of the job scheduling algorithms with respect to QPU utilization and quantum network utilization, beyond the traditional concept of makespan. The discussion is supported by a DQC job scheduling example, where two different strategies are compared in terms of the proposed metrics.
Driven by quantum superposition and entanglement, the swift advancement of quantum computing has highlighted the limitations of classical computation. As a solution, Quantum Networks (QNs) have emerged, offering high-quality entanglement connections and reliable quantum state transmission, enabling a range of applications that exceed the limitations of classical data networks, including quantum communication and distributed quantum computing (DQC). This article delves into key components and concepts such as quantum entanglement, quantum decoherence and entanglement distribution. It then explores quantum remote secure communication technologies, including quantum teleportation, quantum key distribution (QKD), quantum dense coding, quantum repeater technology, and quantum satellite communication. We also provide a detailed introduction to quantum remote entanglement distribution and quantum entanglement routing design, including current research progress and a discussion on the challenges and existing solutions for constructing large-scale QNs. The aim of this article is to provide readers with a fundamental understanding of QNs, an assessment of current research, and insights into the main challenges and solutions in this emerging field. Through these discussions, we hope to help readers better understand the potential and future direction of QNs.
Present quantum computers are constrained by limited qubit capacity and restricted physical connectivity, leading to challenges in large-scale quantum computations. Distributing quantum computations across a network of quantum computers is a promising way to circumvent these challenges and facilitate large quantum computations. However, distributed quantum computations require entanglements (to execute remote gates) which can incur significant generation latency and, thus, lead to decoherence of qubits. In this work, we consider the problem of distributing quantum circuits across a quantum network to minimize the execution time. The problem entails mapping the circuit qubits to network memories, including within each computer since limited connectivity within computers can affect the circuit execution time. We provide two-step solutions for the above problem: In the first step, we allocate qubits to memories to minimize the estimated execution time; for this step, we design an efficient algorithm based on an approximation algorithm for the max-quadratic-assignment problem. In the second step, we determine an efficient execution scheme, including generating required entanglements with minimum latency under the network resource and decoherence constraints; for this step, we develop two algorithms with appropriate performance guarantees under certain settings or assumptions. We consider multiple protocols for executing remote gates, viz., telegates and cat-entanglements. With extensive simulations over NetSquid, a quantum network simulator, we demonstrate the effectiveness of our developed techniques and show that they outperform a scheme based on prior work by 40 to 50% on average and up to 95% in some cases.