Nonreciprocal flow of fluctuations, populations and correlations between doubly coupled bosonic modes

TL;DR

This paper explores how double coupling of two bosonic modes through linear and nonlinear interactions leads to nonreciprocal fluctuation flow, unidirectional correlations, and control over squeezing and coherence properties, despite a Hermitian Hamiltonian.

Contribution

It reveals that double coupling induces non-Hermitian-like dynamics, enabling control over state conversion, unidirectional flow, and squeezing in bosonic modes, which is a novel insight.

Findings

Exceptional point controls state conversion into squeezed states.

Two-photon correlations in reservoirs cause unidirectional flow of populations.

Flow of population creates coherence but limits entanglement.

Abstract

Interesting new correlation and unidirectional properties of two bosonic modes under the influence of environment appear when the modes are mutually coupled through the simultaneously applied linear mode-hopping and nonlinear squeezing interactions. Under such double coupling, it is found that while the Hamiltonian of the system is clearly Hermitian the dynamics of the quadrature components of the field operators can be attributed to non-Hermicity of the system. It is manifested in an asymmetric coupling between the quadrature components which then leads to a variety of remarkable features. In particular, we identify how the emerging exceptional point controls the conversion of thermal states of the modes into single-mode classically or quantum squeezed states. Furthermore, for reservoirs being in squeezed states, we find that the two-photon correlations present in these reservoirs are responsible for unidirectional flow of populations and correlations among the modes and the flow can be controlled by appropriate tuning of the mutual orientation of the squeezed noise ellipses. In the course of analyzing these effects we find that the flow of the population creates the first-order coherence between the modes which, on the other hand rules out an enhancement of the two photon correlations responsible for entanglement between the modes. These results suggest new alternatives for the creation of single mode squeezed fields and the potential applications for controlled unidirectional transfer of population and correlations in bosonic chains.