Quantum random walks in coupled photonic ring resonators

TL;DR

This paper investigates quantum random walks in coupled photonic ring resonators, analyzing their potential for quantum advantage and comparing quantum and classical behaviors through theoretical models, simulations, and experiments.

Contribution

It introduces a family of graph models for these devices, identifies conditions for quantum advantage, and demonstrates how to revert to classical walks by phase averaging.

Findings

Quantum advantage conditions are identified.

Classical walks are recoverable via phase averaging.

Experimental feasibility is demonstrated with polymeric couplers.

Abstract

Quantum random walks use interference to obtain faster state space exploration, which can be used for algorithmic purposes. Photonic technologies provide a natural platform for many recent experimental demonstrations. Here we analyze quantum random walks implemented by coherent light propagation in series-coupled photonic ring resonators. We propose a family of graphs modeling these devices and compare quantum and classical random walks on these structures, calculating steady-state and time-dependent solutions. We obtain conditions for quantum advantage in this setting and show how to recover classical random walks by averaging over quantum phases. Preliminary device feasibility tests are carried out via simulations and experimental results using polymeric directional couplers.