Quantum impurity in a 1D photonic crystal

Quantum impurity problems are described in terms of a single quantum-mechanical degree of freedom interacting with a dissipative reservoir. Superconducting circuits offer an ideal platform for studying the quantum dynamics of artificial atoms embedded in the electromagnetic continuum of a one-dimensional waveguide, reaching non-perturbative coupling regimes in the spin-boson model for an ohmic bath. Parallel experiments have explored transmon qubits strongly coupled to a photonic crystal, where the impurity hybridizes with the band structure resulting in a photonic bound state inside the gap. In this talk we present recent efforts in further pushing the coupling strength with the stepped impedance microwave crystal, using an artificial atom with a large magnetic moment, the fluxonium circuit. The goal of this experiment is to explore how photon scattering inside the waveguide is influenced by the significance of counter-rotating coupling terms and by the nonlinear photon dispersion in the crystal.