# Nonreciprocal slow or fast light in anti-$\mathcal{PT}$-symmetric optomechanics

## TL;DR

This paper demonstrates how tuning an anti-$\mathcal{PT}$-symmetric optomechanical resonator near an exceptional point enables nonreciprocal light transmission and group delay effects, advancing control over laser propagation in non-Hermitian systems.

## Contribution

It introduces a method to achieve nonreciprocal light transmission and group delay in an anti-$\mathcal{PT}$-symmetric spinning resonator near the exceptional point, expanding the applications of non-Hermitian physics.

## Key findings

- High isolation ratio in nonreciprocal light transmission.
- Observation of nonreciprocal group delay and advance.
- Potential for broader applications in $\mathcal{APT}$-symmetric devices.

## Abstract

Non-Hermitian systems with anti-parity-time ($\mathcal{APT}$) symmetry have revealed rich physics beyond conventional systems. Here, we study optomechanics in an $\mathcal{APT}$-symmetric spinning resonator and show that, by tuning the rotating speed to approach the exceptional point (EP) or the non-Hermitian spectral degeneracy, nonreciprocal light transmission with a high isolation ratio can be realized. Accompanying this process, nonreciprocal group delay or advance is also identified in the vicinity of EP. Our work sheds new light on manipulating laser propagation with optomechanical EP devices and, in a broader view, can be extended to explore a wide range of $\mathcal{APT}$-symmetric effects, such as $\mathcal{APT}$-symmetric phonon lasers, $\mathcal{APT}$-symmetric topological effects, and $\mathcal{APT}$-symmetric force sensing or accelerator.