Implementation of a 3 x 3 directionally-unbiased linear optical multiport

TL;DR

This paper demonstrates an experimental 3x3 directionally-unbiased linear optical multiport using fiber optics, enabling more scalable quantum networks by reducing optical path length constraints and simplifying complex quantum walk implementations.

Contribution

The paper presents the first fiber-based experimental realization of a directionally-unbiased 3x3 optical multiport, overcoming coherence length limitations of previous bulk optical setups.

Findings

Successfully implemented a fiber-optic 3x3 multiport

Eliminated the need for long coherence length light sources

Facilitates scalable quantum walk experiments

Abstract

Linear optical multiports are widely used in photonic quantum information processing. Naturally, these devices are directionally-biased since photons always propagate from the input ports toward the output ports. Recently, the concept of directionally-unbiased linear optical multiports was proposed. These directionally-unbiased multiports allow photons to propagate along a reverse direction, which can greatly reduce the number of required linear optical elements for complicated linear optical quantum networks. Here, we report an experimental demonstration of a 3 x 3 directionally-unbiased linear optical fiber multiport using an optical tritter and mirrors. Compared to the previous demonstration using bulk optical elements which works only with light sources with a long coherence length, our experimental directionally-unbiased 3 x 3 optical multiport does not require a long coherence length since it provides negligible optical path length differences among all possible optical trajectories. It can be a useful building block for implementing large-scale quantum walks on complex graph networks.