Generation and stabilization of bound states in the continuum in dissipative Floquet optical lattices

This paper investigates the generation and stabilization of bound states in the continuum (BICs) in a one-dimensional dissipative Floquet lattice. We introduce on-site loss on the two sites neighboring the central hopping defect and analyze the resulting non-Hermitian lattice using Floquet diagonalization and high-frequency expansion. We report the discovery of a stable dark Floquet BIC characterized by a quasienergy with a real part (a value of zero) within the extended band and a vanishing imaginary part, despite the system being purely dissipative. We demonstrate that introducing loss to the two selected sites broadens the parameter window where the BIC exists and effectively protects the BIC against small variations in driving parameters. Our results reveal that increased loss can counterintuitively enhance the stability of the dark Floquet BIC. We further establish that stable dark Floquet BICs can robustly persist even in nonlinear regimes. Our findings provide theoretical support for the experimental realization of stable BICs in dissipative quantum systems.