Directionally-Unbiased Unitary Optical Devices in Discrete-Time Quantum Walks

TL;DR

This paper explores directionally-unbiased optical devices for discrete-time quantum walks, demonstrating significant resource savings over traditional beam-splitter-based systems in photonic quantum information processing.

Contribution

It introduces and analyzes directionally-unbiased optical devices, showing their advantages in reducing hardware complexity for quantum walk implementations.

Findings

Significant reduction in optical components needed for quantum walks.

Effective implementation of quantum walks on graph networks using unbiased devices.

Resource savings compared to traditional directional optical networks.

Abstract

The optical beam splitter is a widely-used device in photonics-based quantum information processing. Specifically, linear optical networks demand large numbers of beam splitters for unitary matrix realization. This requirement comes from the beam splitter property that a photon cannot go back out of the input ports, which we call "directionally-biased". Because of this property, higher dimensional information processing tasks suffer from rapid device resource growth when beam splitters are used in a feed-forward manner. Directionally-unbiased linear-optical devices have been introduced recently to eliminate the directional bias, greatly reducing the numbers of required beam splitters when implementing complicated tasks. Analysis of some originally directional optical devices and basic principles of their conversion into directionally-unbiased systems form the base of this paper. Photonic quantum walk implementations are investigated as a main application of the use of directionally-unbiased systems. Several quantum walk procedures executed on graph networks constructed using directionally-unbiased nodes are discussed. A significant savings in hardware and other required resources when compared with traditional directionally-biased beam-splitter-based optical networks is demonstrated.