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Concurrency and Computation Practice and Experience

Simulating a Quantum Switch With Concurrent Demands

Juan Fernández‐Herrerín‐Álvarez, Francisco Javier González-Castaño, Ana Fernández Vilas

Published Nov 2, 2025• 1 citation
Publisher

Abstract

ABSTRACT Quantum networks rely on entanglement distribution to enable secure communication and distributed quantum computation. Most analytical models address idealized, single‐flow scenarios and overlook the impact of concurrent entanglement requests, limiting their applicability to realistic network conditions. This work studies the behavior of a quantum switch under simultaneous entanglement demands, motivated by the need to understand how concurrency affects link utilization, generation rate, and end‐to‐end fidelity. Our main contribution is a concurrency‐aware switch model that jointly captures capacity and fidelity under multi‐flow conditions, offering the first systematic simulation‐based analysis of this problem. Results show that handling several requests at the same time improves throughput but reduces fidelity once the network is too busy. This highlights the need for scheduling and routing strategies that keep a good balance between efficiency and entanglement quality in future quantum networks.

DOI
10.1002/cpe.70347

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ABSTRACT Quantum networks rely on entanglement distribution to enable secure communication and distributed quantum computation. Most analytical models address idealized, single‐flow scenarios and overlook the impact of concurrent entanglement requests, limiting their applicability to realistic network conditions. This work studies the behavior of a quantum switch under simultaneous entanglement demands, motivated by the need to understand how concurrency affects link utilization, generation rate, and end‐to‐end fidelity. Our main contribution is a concurrency‐aware switch model that jointly captures capacity and fidelity under multi‐flow conditions, offering the first systematic simulation‐based analysis of this problem. Results show that handling several requests at the same time improves throughput but reduces fidelity once the network is too busy. This highlights the need for scheduling and routing strategies that keep a good balance between efficiency and entanglement quality in future quantum networks.
This paper investigates resource allocation for entanglement distribution in multi-node, multi-channel quantum networks at the metropolitan scale. A multi-slot quantum network simulation framework is developed across physical and network layers, incorporating heterogeneous link characteristics, limited quantum memories, request queuing, retry mechanisms, and concurrent entanglement distribution. Based on this framework, a centralized scheduling architecture is proposed to coordinate quantum memories, communication channels, and routing paths for multiple simultaneous entanglement requests. Three classes of resource allocation strategies are evaluated: heuristic approaches, a mixed-integer linear programming (MILP) optimization method, and a Proximal Policy Optimization (PPO)-based reinforcement learning approach. The heuristic schemes reveal fundamental trade-offs between request delay and entanglement success rate: Dynamic Efficient minimizes delay, Success Enhancement improves success probability through adaptive multi-path allocation, and Static Efficient provides a balance between these objectives. The MILP approach achieves optimized resource allocation by jointly considering request handling and multi-path assignment, while the PPO-based method learns adaptive scheduling policies to improve overall performance. Simulation results demonstrate that these approaches provide different performance advantages in terms of request delay, entanglement success rate, capacity utilization, and request handling rate, highlighting the trade-offs between efficiency and reliability in metropolitan-scale quantum network scheduling.
Quantum switches are envisioned to be an integral component of future entanglement distribution networks. They can provide high quality entanglement distribution service to end-users by performing quantum operations such as entanglement swapping and entanglement purification. In this work, we characterize the capacity region of such a quantum switch under noisy channel transmissions and imperfect quantum operations. We express the capacity region as a function of the channel and network parameters (link and entanglement swap success probability), entanglement purification yield and application level parameters (target fidelity threshold). In particular, we provide necessary conditions to verify if a set of request rates belong to the capacity region of the switch. We use these conditions to find the maximum achievable end-to-end user entanglement generation throughput by solving a set of linear optimization problems. We develop a max-weight scheduling policy and prove that the policy stabilizes the switch for all feasible request arrival rates. As we develop scheduling policies, we also generate new results for computing the conditional yield distribution of different classes of purification protocols. The conclusions obtained in this work can yield useful guidelines for subsequent quantum switch designs.
Quantum networks, as a pivotal platform to support numerous quantum applications, have the potential to far exceed traditional communication networks. Establishing end-to-end entanglement connections with guaranteed fidelity is a key prerequisite for realizing the functionality of quantum networks. Entanglement purification techniques are commonly used in the entanglement distribution process to provide end-to-end entanglement connections that meet the fidelity requirements. Since the purification operation sacrifices a certain amount of entanglement resources, it is critical and challenging to efficiently utilize the scarce entanglement resources in quantum networks with concurrent competing requests. To address this problem, we propose a novel demand-oriented resource scheduling (DRS) algorithm. Considering the overall network demand, DRS introduces a congestion factor to evaluate the resource demand of each link, and performs purification operations sequentially based on the congestion level of the links, thus avoiding the excessive consumption of entanglement resources of bottleneck links. Extensive simulation results show that the DRS algorithm can achieve higher network throughput with similar resource conversion rates compared to traditional resource allocation schemes. Our work provides a new scheme for the resource scheduling problem under concurrent competing requests, which can promote the further development of existing entanglement routing techniques.
We consider a star-shaped quantum network with a quantum switch in the center serving a number of requests, each characterized by two non-classical QoS requirements, the end-to-end entanglement delivery rate and the fidelity of the delivered entanglements. The central task of the switch is to allocate the limited entanglement resources among requests to maximize the system performance. We formulate the fundamental entanglement distribution problem where the switch decides 1) which requests to admit, and 2) as multiple requests may share a same quantum link, how to distributed the limited link-level entanglement resources among those competing requests. We then design a framework of joint entanglement purification scheduling and distribution for quantum switches. Our entanglement purification scheduling algorithm seeks to use minimal link-level entanglement resources to satisfy the QoS requirement of a single request. Our entanglement distribution algorithm further allocates the limited entanglement resources among multiple requests to maximize the overall utility by integrating the designed entanglement purification scheduling algorithm. We establish theoretical performance guarantee of our proposition, which is complemented by extensive numerical experiments demonstrating its effectiveness in a variety of network settings.
Quantum switches are critical components in quantum networks, distributing maximally entangled pairs among end nodes by entanglement swapping. In this work, we design protocols that schedule entanglement swapping operations in quantum switches. Entanglement requests randomly arrive at the switch, and the goal of an entanglement swapping protocol is to stabilize the quantum switch so that the number of unfinished entanglement requests is bounded with a high probability. We determine the capacity region for the rates of entanglement requests and develop entanglement swapping protocols to stabilize the switch. Among these protocols, the on-demand protocols are not only computationally efficient, but also achieve high fidelity and low latency demonstrated by results obtained using a quantum network discrete event simulator.
With a growing number of quantum networks in operation, there is a pressing need for performance analysis of quantum switching technologies. A quantum switch establishes, distributes, and maintains entanglements across a network. In contrast to a classical switching fabric, a quantum switch is a two-sided queueing network. The switch generates Link-Level Entanglements (LLEs) across links that connect users to the switch, which are then fused to process the network's entanglement requests. First, we characterize the capacity region that is defined as the set of entanglement request rates for which there exists a scheduling policy stabilizing the system. We then show that a sequence of Max-Weight policies that we propose achieve throughput optimality in the asymptotic sense. Our proof techniques analyse a two-time scale separation phenomenon at the fluid scale for a general switch topology. This allows us to demonstrate that the optimal fluid dynamics are given by a scheduling algorithm that solves a certain average reward Markov Decision Process.