Virtual atom–photon bound states and spontaneous emission control

In waveguide quantum electrodynamics (QED) systems, atomic radiation emission is shaped by photonic environment and collective atom interactions, offering promising applications in quantum technologies. In particular, atom–photon bound states, inhibiting a complete spontaneous decay of the atom, can be realized through waveguide dispersion engineering or by utilizing giant atoms. While steady-state bound states are well understood, transient or virtual bound states remain less explored. Here, we investigate transient atom–photon bound states, arising from initial atom–photon entanglement, and propose methods to slow down spontaneous atomic decay.