Multi-photon quantum interference with high visibility using multiport beam splitters

TL;DR

This paper demonstrates how multiport beam splitters can enhance interference contrast in multi-photon PDC experiments, enabling more effective tests of quantum nonlocality and potential applications in quantum communication.

Contribution

It introduces a scheme using multiport beam splitters as POVM filters to improve interference contrast in high-pump multi-photon PDC experiments.

Findings

Enhanced interference contrast with multiport beam splitters

Feasibility of CHSH-Bell inequality tests with this setup

Potential applications in reducing communication complexity

Abstract

Multi-photon states can be produced in multiple parametric down conversion (PDC) processes. The nonlinear crystal in such a case is pumped with high power. In theory, the more populated these states are, the deeper is the conflict with local realistic description. However, the interference contrast in multi-photon PDC experiments can be quite low for high pumping. We show how the contrast can be improved. The idea employs currently accessible optical devices, the multiport beam splitters. They are capable of splitting the incoming light in one input mode to $M$ output modes. Our scheme works as a POVM filter. It may provide a feasible CHSH-Bell inequality test, and thus can be useful in e.g. schemes reducing communication complexity.