Quantum Circuit Switching with One-Way Repeaters in Star Networks

TL;DR

This paper compares sequential and parallel quantum state distribution protocols in star network topologies, revealing trade-offs in request handling and distance limitations due to repeater processing delays.

Contribution

It introduces a queuing theory-based analysis of quantum circuit switching protocols, highlighting the advantages of parallel distribution for request rate and the impact of repeaters on distance.

Findings

Parallel distribution increases request success rate.

Sequential distribution supports more users simultaneously.

Repeaters limit maximum user distance due to processing delays.

Abstract

Distributing quantum states reliably among distant locations is a key challenge in the field of quantum networks. One-way quantum networks address this by using one-way communication and quantum error correction. Here, we analyze quantum circuit switching as a protocol to distribute quantum states in one-way quantum networks. In quantum circuit switching, pairs of users can request the delivery of multiple quantum states from one user to the other. After waiting for approval from the network, the states can be distributed either sequentially, forwarding one at a time along a path of quantum repeaters, or in parallel, sending batches of quantum states from repeater to repeater. Since repeaters can only forward a finite number of quantum states at a time, a pivotal question arises: is it advantageous to send them sequentially (allowing for multiple requests simultaneously) or in parallel (reducing processing time but handling only one request at a time)? We compare both approaches in a quantum network with a star topology. Using tools from queuing theory, we show that requests are met at a higher rate when packets are distributed in parallel, although sequential distribution can generally provide service to a larger number of users simultaneously. We also show that using a large number of quantum repeaters to combat channel losses limits the maximum distance between users, as each repeater introduces additional processing delays. These findings provide insight into the design of protocols for distributing quantum states in one-way quantum networks.