Experimental demonstration of a directionally-unbiased linear-optical multiport

TL;DR

This paper demonstrates a novel linear-optical multiport that allows photons to travel reversibly, enabling more efficient quantum walk implementations and reducing hardware complexity in quantum simulations.

Contribution

The authors experimentally realize a directionally-unbiased linear-optical multiport, enabling reversible photon paths and more resource-efficient quantum walk applications.

Findings

Reconstructed a unitary three-edge vertex matrix with linear optics.

Demonstrated reversibility of photon direction in the multiport.

Showed potential for more efficient quantum simulations.

Abstract

All existing optical quantum walk approaches are based on the use of beamsplitters and multiple paths to explore the multitude of unitary transformations of quantum amplitudes in a Hilbert space. The beamsplitter is naturally a directionally biased device: the photon cannot travel in reverse direction. This causes rapid increases in optical hardware resources required for complex quantum walk applications, since the number of options for the walking particle grows with each step. Here we present the experimental demonstration of a directionally-unbiased linear-optical multiport, which allows reversibility of photon direction. An amplitude-controllable probability distribution matrix for a unitary three-edge vertex is reconstructed with only linear-optical devices. Such directionally-unbiased multiports allow direct execution of quantum walks over a multitude of complex graphs and in tensor networks. This approach would enable simulation of complex Hamiltonians of physical systems and quantum walk applications in a more efficient and compact setup, substantially reducing the required hardware resources.