Quantum electrodynamics near a photonic bandgap

Abstract

Using a superconducting transmon qubit coupled to a microwave photonic crystal one can study intriguing strong-coupling effects such as the emergence of localized cavity modes within the photonic bandgap. Photonic crystals are a powerful tool for the manipulation of optical dispersion and density of states, and have thus been used in applications from photon generation to quantum sensing with nitrogen vacancy centres and atoms1,2. The unique control provided by these media makes them a beautiful, if unexplored, playground for strong-coupling quantum electrodynamics, where a single, highly nonlinear emitter hybridizes with the band structure of the crystal. Here we demonstrate that such a hybridization can create localized cavity modes that live within the photonic bandgap, whose localization and spectral properties we explore in detail. We then demonstrate that the coloured vacuum of the photonic crystal can be employed for efficient dissipative state preparation. This work opens exciting prospects for engineering long-range spin models3,4 in the circuit quantum electrodynamics architecture, as well as new opportunities for dissipative quantum state engineering.