Bound states in the continuum: A quantum photonic perspective

Bound states in the continuum (BICs), first proposed by von Neumann and Wigner in 1929, describe localized states embedded within a continuum yet completely decoupled from radiative channels. Once regarded as a theoretical curiosity in quantum mechanics, BICs have since been realized across diverse physical systems, including electronic, acoustic, and photonic platforms, where they exhibit effectively infinite quality factors and negligible radiative loss. In photonics, the advent of metasurfaces and photonic crystals has enabled precise control of geometry and permittivity, transforming ideal BICs into experimentally accessible quasi-BICs that provide extreme spectral confinement and enhanced light–matter interactions. These unique properties offer robust and tunable platforms for quantum state generation and control at the nanoscale. This Review summarizes recent progress in BIC research from a quantum photonic perspective, covering their roles in quantum light generation, nonlinear optics, and strong light–matter coupling. It also highlights emerging frontiers, including topologically protected coherent BIC platforms, compact on-chip BIC architectures, and plasmonic BICs for room-temperature quantum devices. Together, these developments mark the evolution of BICs from a quantum mechanical concept to a cornerstone of next-generation quantum photonic technologies.