Interference-Induced Bound States in the Continuum in Optical Giant Atoms

The giant atom paradigm, where a single quantum emitter couples to a continuum at multiple discrete points, has enabled unprecedented control over light-matter interactions, including decoherence-free subspaces and chiral emission. However, realizing these non-local effects beyond the microwave regime remains a significant challenge due to the diffraction limit. Here, we theoretically propose a photonic analog of giant atoms operating at optical frequencies, utilizing a quantum emitter resonantly coupled to a pair of spatially separated single-mode cavities interacting with a common 1D photonic continuum. By rigorously deriving the effective non-Hermitian Hamiltonian and integrating out the bath degrees of freedom, we demonstrate that the interference between cavity-mediated emission pathways leads to the formation of robust Bound States in the Continuum (BICs). These interference-induced dark states allow for the infinite trapping of excitation within the emitter-cavity subsystem, effectively shielding it from radiative decay. Our results extend the giant atom toolbox to the optical domain, offering a scalable architecture for integrated quantum photonics and quantum interconnects.