PT-symmetry breaking and laser-absorber modes in optical scattering systems

TL;DR

This paper explores PT-symmetry breaking in optical scattering systems, revealing how such systems transition from norm-preserving states to ones with amplification and loss, and identifying conditions for laser-absorber modes.

Contribution

It provides a general scattering matrix framework for PT-symmetric optical structures and characterizes the conditions for laser-absorber modes at symmetry-breaking points.

Findings

Existence of PT-symmetry breaking transition in scattering eigenstates

Identification of laser-absorber modes at S-matrix pole-zero coincidence

Demonstration of a unified formalism for PT-symmetric optical systems

Abstract

Using a scattering matrix formalism, we derive the general scattering properties of optical structures that are symmetric under a combination of parity and time-reversal (PT). We demonstrate the existence of a transition beween PT-symmetric scattering eigenstates, which are norm-preserving, and symmetry-broken pairs of eigenstates exhibiting net amplification and loss. The system proposed by Longhi, which can act simultaneously as a laser and coherent perfect absorber, occurs at discrete points in the broken symmetry phase, when a pole and zero of the S-matrix coincide.