# Exceptional Points in Random-Defect Phonon Lasers

## TL;DR

This paper demonstrates that surpassing an exceptional point in optomechanical devices with defects can enhance phonon gain and number, challenging the traditional view that defects are purely detrimental.

## Contribution

It introduces a non-Hermitian phonon-defect model showing that exceptional points can improve phonon lasing despite defect losses.

## Key findings

- Enhanced phonon gain beyond defect losses at EPs
- Counterintuitive phonon number increase with defects
- Effective non-Hermitian model explains the phenomenon

## Abstract

Intrinsic defects in optomechanical devices are generally viewed to be detrimental for achieving coherent amplification of phonons, and great care has thus been exercised in fabricating devices and materials with no (or a minimal number of) defects. Contrary to this view, here we show that, by surpassing an exceptional point (EP), both the mechanical gain and the phonon number can be enhanced despite increasing defect losses. This counterintuitive effect, well described by an effective non-Hermitian phonon-defect model, provides a mechanical analog of the loss-induced purely optical lasing. This opens the way to operating random-defect phonon devices at EPs.