Quantum echo route towards exceptional points in Anderson localized lasers

TL;DR

This paper demonstrates the statistical occurrence of exceptional points in Anderson localized lasers by exploiting quantum echoes, providing a new route to observe non-Hermitian degeneracies in disordered photonic systems.

Contribution

It introduces a novel approach to realize and detect exceptional points in disordered systems using quantum echoes and statistical analysis of multiple disorder configurations.

Findings

Quantum echoes reveal mode coupling in Anderson localized lasers.

Exceptional points are identified by spectral coalescence and vanishing echoes.

Lasing intensity peaks at exceptional points with square-Lorentzian lineshape.

Abstract

Exceptional points, that are spectral degeneracies in the parameter space of non-Hermitian systems, have evoked a massive interest in the optical domain owing to their striking consequences on optical behavior of commonly known systems. Through careful engineering of gain and loss, exceptional points have been demonstrated in a variety of photonic systems ranging from optical fibers to chaotic cavities, exhibiting extra-ordinary phenomena and augmented functionalities. However, in the domain of disordered systems, there are still no realizations of exceptional points even though mode-coupling and non-Hermitian behavior is amply demonstrated. The obvious challenge lies in the probabilistic nature of disorder, which is a difficult candidate for parametric control. Here, we exploit the probabilistic nature of Anderson localizing systems by implementing thousands of disorder configurations. We demonstrate statistical occurrences of lasing over exceptional points. Our route towards exceptional points begins with detection of quantum echoes, which are temporal signatures of coupling between modes. Quantum echoes unambiguously set apart two coupled modes from a pair of two isolated modes that are spectrally close perchance. Simultaneous temporal, spectral and spatial investigations provide corroborative evidence of the convergence of eigenvalues and eigenvectors in the approach to the exceptional points. Ultimately, the vanishing of the echo and coalescence of spectral peaks and spatial intensity distributions, accompanied by the square-Lorentzian lineshape of lasing peaks, identify the exceptional point, at which the lasing intensity is seen to be significantly higher.