Entanglement swapping enables entanglement distribution between distant nodes in quantum networks. This paper aims at designing remote entanglement distribution (RED) protocols to schedule entanglement swapping for maximizing the entanglement distribution rate (EDR). The concept of Enodes is introduced to represent the entangled quantum bit pairs in the network. With such a concept, we can transform the design of the optimal RED protocols into solving certain linear programming problems. In addition, we study RED in the homogeneous repeater chain, which is a basic and critical quantum network. Specifically, we determine the closed-form expression for the maximum EDR in such a setting. Our results will enable the distribution of long-distance entanglement with noisy intermediate-scale quantum (NISQ) technologies.
Entanglement swapping enables entanglement distribution between distant nodes in quantum networks. This paper aims at designing remote entanglement distribution (RED) protocols to schedule entanglement swapping for maximizing the entanglement distribution rate (EDR). The concept of Enodes is introduced to represent the entangled quantum bit pairs in the network. With such a concept, we can transform the design of the optimal RED protocols into solving certain linear programming problems. In addition, we study RED in the homogeneous repeater chain, which is a basic and critical quantum network. Specifically, we determine the closed-form expression for the maximum EDR in such a setting. Our results will enable the distribution of long-distance entanglement with noisy intermediate-scale quantum (NISQ) technologies.
Distributing entanglement between distant nodes is an essential task in quantum networks. To achieve this task, quantum repeaters have been introduced to perform entanglement swapping. This paper offers a design of remote entanglement distribution (RED) protocols that maximize the entanglement distribution rate (EDR). We introduce the concept of enodes, representing the entangled quantum bit (qubit) pairs in the network. This concept enables us to design the optimal RED protocols based on the solutions of some linear programming problems. Moreover, we investigate RED in a homogeneous repeater chain, which is a building block for many quantum networks. In particular, we determine the maximum EDR for homogeneous repeater chains in a closed form. Our results enable the distribution of long-distance entanglement with noisy intermediate-scale quantum (NISQ) technologies and provide insights into the design and implementation of general quantum networks.
Remote entanglement distribution plays a crucial role in large-scale quantum networks, and the key enabler for entanglement distribution is quantum routers (or repeaters) that can extend the entanglement transmission distance. However, the performance of quantum routers is far from perfect yet. Amongst the causes, the limited quantum memories in quantum routers largely affect the rate and efficiency of entanglement distribution. To overcome this challenge, this paper presents a new modeling for the maximization of entanglement distribution rate (EDR) on a memory-limited path, which is then transformed into entanglement generation and swapping sub-problems. We propose a greedy algorithm for short-distance entanglement generation so that the quantum memories can be efficiently used. As for the entanglement swapping sub-problem, we model it using an Entanglement Graph (EG), whose solution is yet found to be at least NP-complete. In light of it, we propose a heuristic algorithm by dividing the original EG into several sub-problems, each of which can be solved using dynamic programming (DP) in polynomial time. By conducting simulations, the results show that our proposed scheme can achieve a high EDR, and the developed algorithm has a polynomial-time upper bound and reasonable average runtime complexity.
Remote entanglement distribution plays a crucial role in quantum networks, which can support many essential and exciting quantum applications. As the network scale expands, it is urgent to design a general and efficient remote entanglement distribution protocol. Nowadays, connection-oriented remote entanglement distribution protocols are available to achieve reliable entanglement distribution. However, in memory-limited quantum networks, connection-oriented entanglement distribution protocols cannot utilize entanglement resources fully and increase the delay of End-to-End (E2E) entanglement connection establishment. To overcome these shortcomings of existing entanglement distribution protocols, we design a connectionless remote entanglement distribution protocol to let Source-Destination (S-D) pairs compete for entanglement resources simultaneously. In our protocol, a fair request scheduling algorithm is proposed to reduce the waiting time without entanglement connections between S-D pairs. Furthermore, a fast scheduling trigger mechanism is proposed to perform entanglement swapping timely to reduce the delay of E2E entanglement connection establishment. The simulation results show that the designed protocol has advantages in terms of resource utilization, throughput, the service completion time of S-D pairs, and the maximum waiting time, compared with the existing remote entanglement distribution protocol.
First-generation quantum repeaters are essential in distributing entanglement over long distances since they could mitigate losses in optical fiber. Repeaters split the total distance into shorter, easier to generate links. Then, entanglement swapping establishes long range entanglement by performing local measurements at the repeaters and heralding their results. In this work, we develop an analytical model that estimates the impact of decoherence during heralding for a given protocol. Furthermore, we identify a competition between two phenomena: as repeater count increases, so does entanglement generation, but the additive impact of memory decoherence on final entanglement rate increases too. Therefore, we find that an optimal number of repeaters exists. These findings could lead the design of future quantum networks, both in the inter-repeater distance and swapping timings.
Entanglement-based quantum networks can provide unconditionally secure communication by distributing entangled pairs between distant end nodes. To achieve end-to-end entanglement distribution, multiple operations of entanglement swapping in a quantum repeater chain are always required. However, due to the non-determinism of entanglement swapping caused by imperfect physical devices, the execution pattern of swapping operations has a direct impact on the performance of entanglement distribution, which can be categorized into an entanglement access control (EAC) problem. In this article, we attribute the EAC problem to two aspects: the matching optimization within quantum nodes, and the swapping conflict avoidance between quantum nodes. Accordingly, we propose an asynchronous entanglement distribution protocol which contains a custom weighted maximum matching algorithm, and a reliable signaling interaction mechanism to avoid a swapping conflict, respectively. Based on the proposed protocol, quantum repeaters autonomously decide their behaviors and spontaneously construct the end-to-end entangled pairs asynchronously. Simulation results show that our protocol can significantly improve the entanglement distribution rate and fidelity of end-to-end entangled pairs while simplifying the deployment and management process of the quantum networks.
Quantum networks create a completely new way for communication, and the most important function of a quantum network is to generate long-distance quantum entanglement to serve a number of quantum applications. As the scale of the network expands, in order to establish end-to-end entanglement between two remote nodes, entangled pairs need to be generated and distributed among multiple repeaters along the path from the source to the destination, which requires a specific protocol to negotiate resource allocations and quantum operations among the repeaters. Thus, to realize such remote entanglement distribution in a quantum network, designing a stable and reliable protocol becomes urgent and necessary. In this article, we focus on how to guarantee the generation rate of entangled pairs between any two quantum nodes to meet the requirements of various quantum applications in a large-scale quantum network. We present a connection-oriented entanglement distribution protocol inspired by the connection-oriented communication model in classical networks. Our protocol is located in the network layer of the quantum network to enable end-to-end quantum communication. Three main features are provided by the proposed protocol: 1) it is reliable and can guarantee the successful entanglement generation; 2) it can reduce the influence of quantum decoherence via reducing the latency caused by resource competition; and 3) it can guarantee the rate of generating entanglement between two quantum nodes according to the requirement of quantum applications.