Unconventional Singularity in Anti-Parity-Time Symmetric Cavity Magnonics

TL;DR

This paper demonstrates the coexistence of two distinct singularities, an exceptional point and a bound state in the continuum, in an anti-PT symmetric cavity magnonics system, revealing a hybrid state with unique properties.

Contribution

It introduces a novel anti-PT symmetric cavity magnonics system capable of hosting two different singularities simultaneously, a feature not previously observed.

Findings

Observation of exceptional points via magnon damping tuning

Identification of unconventional bound states in the continuum

Coexistence of maximal superposition and slow light at the singularities

Abstract

By engineering an anti-parity-time (anti-PT) symmetric cavity magnonics system with precise eigenspace controllability, we observe two different singularities in the same system. One type of singularity, the exceptional point (EP), is produced by tuning the magnon damping. Between two EPs, the maximal coherent superposition of photon and magnon states is robustly sustained by the preserved anti-PT symmetry. The other type of singularity, arising from the dissipative coupling of two anti-resonances, is an unconventional bound state in the continuum (BIC). At the settings of BICs, the coupled system exhibits infinite discontinuities in the group delay. We find that both singularities co-exist at the equator of the Bloch sphere, which reveals a unique hybrid state that simultaneously exhibits the maximal coherent superposition and slow light capability.