Quantum optics of lossy asymmetric beam splitters

TL;DR

This paper provides a theoretical analysis of quantum interference at lossy asymmetric beam splitters, revealing how losses enable tunable quantum interference and supporting experimental advances in complex multimode quantum systems.

Contribution

It introduces a formalism for understanding quantum interference in lossy beam splitters, highlighting the tunability enabled by losses in passive optical circuits.

Findings

Losses enable tunable quantum interference.

Theoretical framework supports experimental programmable interference.

Applicable to multimode and opaque scattering media.

Abstract

We theoretically investigate quantum interference of two single photons at a lossy asymmetric beam splitter, the most general passive 2$\times$2 optical circuit. The losses in the circuit result in a non-unitary scattering matrix with a non-trivial set of constraints on the elements of the scattering matrix. Our analysis using the noise operator formalism shows that the loss allows tunability of quantum interference to an extent not possible with a lossless beam splitter. Our theoretical studies support the experimental demonstrations of programmable quantum interference in highly multimodal systems such as opaque scattering media and multimode fibers.