Quantum annealing in the NISQ era: railway conflict management

TL;DR

This paper explores the application of quantum annealing to real-world railway conflict management problems in the NISQ era, demonstrating the current limitations and potential of quantum hardware for complex scheduling tasks.

Contribution

It introduces a QUBO model for railway dispatching problems compatible with quantum annealers and evaluates its performance on real-life instances using D-Wave hardware.

Findings

Quantum annealing can model railway conflict problems.

Current quantum annealers struggle with real-world instances.

Newer quantum annealer generations perform worse on these problems.

Abstract

We are in the Noisy Intermediate-Scale Quantum (NISQ) devices' era, in which quantum hardware has become available for application in real-world problems. However, demonstrating the usefulness of such NISQ devices are still rare. In this work, we consider a practical railway dispatching problem: delay and conflict management on single-track railway lines. We examine the issue of train dispatching consequences caused by the arrival of an already delayed train to the network segment being considered. This problem is computationally hard and needs to be solved almost in real-time. We introduce a quadratic unconstrained binary optimization (QUBO) model of this problem, compatible with the emerging quantum annealing technology. The model's instances can be executed on present-day quantum annealers. As a proof-of-concept, we solve selected real-life problems from the Polish railway network using D-Wave quantum annealers. As a reference, we also provide solutions calculated with classical methods, including those relevant to the community (linear integer programming) and a sophisticated algorithm based on tensor networks for solving Ising instances. Our preliminary results illustrate the degree of difficulty of real-life railway instances for the current quantum annealing technology. Moreover, our analysis shows that the new generation of quantum annealers (the advantage system) perform much worse on those instances than its predecessor.