Tunable ultrahigh broadband reflection via collective atom-atom interaction in a waveguide-QED system

We present a scheme for achieving broadband complete reflection by constructing photonic band gap via collective atom-atom interaction in a one-dimensional (1D) waveguide quantum electrodynamics (QED) system. Moreover, we propose several strategies to further expand the ultrahigh-reflection windows, including increasing the number of atoms with separations near the Bragg distance and inducing gradient frequency modulation among the atoms. The center frequency and bandwidth of the ultrahigh-reflection window are dynamically adjustable by applying external electromagnetic field. The results here can enrich the many-body physics of the waveguide-QED system and offer a pathway for achieving broadened ultrahigh reflection in a controllable way, which can find important applications in the realms of chip-integrated band filter, quantum storage, optical switching, and wavelength-selective devices.