Curator's Take
This article reports the first concrete proposal for a bound state in the continuum (BIC) that lives in a fully quantum‑optical setting, showing how a driven multi‑level Jaynes–Cummings system can host a perfectly localized Fock‑state mode despite lying inside a continuous spectrum. By mapping the problem onto two topological Su‑Schrieffer‑Heeger chains and exploiting destructive interference between their zero modes, the authors demonstrate a spectroscopic signature—a discrete peak embedded in a broadband background—that could be observed with a single trapped ion, linking BIC physics to near‑term quantum hardware platforms. If realized, such protected photonic excitations may offer new routes for decoherence‑resistant storage or processing of quantum information, although experimental verification will still need to overcome the precise control required for the multi‑level drive and coupling symmetry.
— Mark Eatherly
Summary
Bound states in the continuum (BICs) are counterintuitive localized states that lie within the continuum of extended states. While extensively realized and utilized in classical wave systems, it is still unclear what a close analog of BICs would be, and how to extract their experimental signature in quantum-optical settings -- where the wave field itself is quantized into bosonic excitations. Here, we present a paradigmatic quantum-optical model consisting of a driven multi-level Jaynes-Cummings (JC) system, featuring few quantum degrees of freedom yet capable of hosting a BIC. Using the concept of a Fock-state lattice (FSL), this model can be mapped to an extended structure comprising two semi-infinite inhomogeneous Su-Schrieffer-Heeger (SSH) chains coupled to a common continuum. An appropriate quantum superposition of two topological zero modes from the separate chains forms a BIC that remains perfectly localized in the Fock-state dimension within the continuum spectrum, due to complete decoupling from the common continuum via destructive quantum interference. We further develop a method to extract the spectroscopic signature of the BIC -- a discrete peak embedded in a continuous background -- by Fourier-transforming the time-dependent dynamics of the system's chiral-symmetry operator. A highly feasible experimental proposal using a single trapped ion is provided. Our work bridges BIC physics with quantum optics, opening a pathway to harnessing such exotic states at the quantum limit.