Matching Queues with Abandonments in Quantum Switches: Stability and Throughput Analysis

Inspired by quantum switches, we consider a discrete-time multi-way matching system with two classes of arrivals: requests for entangled pair of qubits between two nodes, and qubits from each node that can be used to serve the requests. An important feature of this model is that qubits decohere and so abandon over time. In contrast to classical server-based queueing models, the combination of queueing, server-less multi-way matching, and abandonment make the analysis a challenging problem. The primary focus of this paper is to study a simple system consisting of two types of requests and three types of qubits (dubbed the W-topology) operating under a Max-Weight policy. In this setting, we characterize the stability region under the Max-Weight policy by adopting a two-time scale fluid limit to get a handle on the abandonments. In particular, we show that Max-Weight is throughput optimal and that its stability region is larger than the convex hull of the throughputs that can be achieved by non-idling policies when the requests are infinitely backlogged. Moreover, despite the use of a policy that prioritizes the largest requests queue, we show that there can be a counterintuitive behavior in the system: the longest requests queue can have a positive drift for some time even if the overall system is stable.