Exceptional points with memory in a microcavity Brillouin laser

Abstract

Exceptional points (EPs), universally present in non-Hermitian systems, often reveal some critical behaviors such as topological encircling chirality and ultrahigh enhanced sensing near such singularities. However, most of the experimental realizations of EPs have been limited to the linear regime, where system nonlinearity has been omitted. Here, we experimentally observe two distinct EPs with opposite hermiticities and demonstrate a parity–time phase transition with exotic memory effects near the EPs in a nonlinear and non-Hermitian system based on a stimulated Brillouin laser in an optical microcavity. The self-phase modulation induced nonlinearity effectively alters the EP location, surprisingly, in an asymmetric manner, resulting in a bistable memory effect. Moreover, two EPs with opposite hermiticities in the same system are found to show quite distinct behaviors in such a memory effect. This scheme completes the studies of non-Hermitian physics in a more general scenario by including nonlinearity and paves the way toward optical memory for all-optical signal processing and quantum information.