Nonclassical light at exceptional points of a quantum PT-symmetric two-mode system

TL;DR

This paper investigates how exceptional points in a quantum PT-symmetric two-mode system can enhance nonclassical light generation, analyzing quantum correlations and fluctuations near these degeneracies.

Contribution

It reveals the role of exceptional points in boosting nonclassical light properties in a quantum PT-symmetric system with gain, damping, and Kerr nonlinearities.

Findings

Exceptional points enhance nonlinear interactions and nonclassicality.

Conditions for optimal nonclassical-light generation are identified.

Quantum fluctuations influence entanglement and squeezing dynamics.

Abstract

A two-mode optical parity-time (PT) symmetric system, with gain and damping, described by a quantum quadratic Hamiltonian with additional small Kerr-like nonlinear terms, is analyzed from the point of view of nonclassical-light generation. Two kinds of stationary states with different types of (in)stability are revealed. Properties of one of these are related to the presence of semiclassical exceptional points, i.e., exotic degeneracies of the non-Hermitian Hamiltonian describing the studied system without quantum jumps. The evolution of the logarithmic negativity, principal squeezing variances, and sub-shot-noise photon-number correlations, considered as entanglement and non-classicality quantifiers, is analyzed in the approximation of linear-operator corrections to the classical solution. Suitable conditions for nonclassical-light generation are identified in the oscillatory regime, especially at and around exceptional points that considerably enhance the nonlinear interaction and, thus, the non-classicality of the generated light. The role of quantum fluctuations, inevitably accompanying attenuation and amplification in the evolution of quantum states, is elucidated. The evolution of the system is analyzed for different initial conditions.