Quantum Beam Splitter as a Quantum Coherence Controller

TL;DR

This paper introduces a tunable quantum beam splitter based on a $ ext{PT}$-symmetric system that can generate and control asymmetric quantum coherence, enabling advanced manipulation of weak quantum light for photonic applications.

Contribution

It presents a novel $ ext{PT}$-symmetric quantum beam splitter capable of asymmetric coherence control and photon blockade, expanding quantum photonics capabilities.

Findings

Produces anti-bunched and bunched photons with high asymmetry

Achieves perfect photon blockade with zero $g^{(2)}(0)$

Demonstrates coherence control beyond Hong-Ou-Mandel effect

Abstract

We propose a quantum beam splitter (QBS) with tunable reflection and transmission coefficients. More importantly, our device based on a Hermitian parity-time ($\mathcal{PT}$) symmetric system enables the generation and manipulation of asymmetric quantum coherence of the output photons. For the interference of two weak coherent-state inputs, our QBS can produce anti-bunched photons from one output port and bunched photons from the other, showcasing high parity asymmetry and strong coherence control capabilities. Beyond the Hong-Ou-Mandel effect, perfect photon blockade with vanishing $g^{(2)}(0)$ is achievable in two-photon interference. These striking effects of the QBS fundamentally arise from the parity-symmetry-breaking interaction and the quantum interference between the photon scattering channels. Our results could inspire novel applications and the development of innovative photonic devices for the manipulation of weak quantum light.