Dual-state control of lasing and absorption via conjugate exceptional points

Abstract

Lasing and coherent perfect absorption (CPA) are time-reversed manifestations of non-Hermitian light-matter interactions. While exceptional points (EPs) have been extensively explored for controlling lasing dynamics, their role in the concurrent manipulation of lasing and absorption remains largely unexplored. Here, we demonstrate the emergence of a pair of conjugate second-order EPs (EP2s) in a gain-loss-engineered Fabry-P\'erot microcavity that enables dual-state operation involving both coherent amplification and absorption. By spatially tailoring gain and loss, we realize two such EP2s: one associated with the coalescence of coupled scattering-matrix poles and the other, its conjugate, arising from the coalescence of corresponding zeros, thereby directly linking the amplifying and absorbing branches of the system. Leveraging the branch-point topology of these conjugate EP2s, we adiabatically encircle them in the gain-loss parameter space and achieve deterministic state permutation, enabling multiple reconfigurable switching schemes for the controlled generation and manipulation of threshold lasing and CPA. Notably, simultaneous encirclement of these conjugate EP2s yields a coordinated dual-state switching protocol, resulting in a frequency-matched coexistence of lasing and absorption responses within the same cavity. Our results establish an EP-based framework for unified and flexible control of lasing and absorption in non-Hermitian photonic systems.