Radiative Properties of an Artificial Atom coupled to a Josephson Junction Array

Abstract

We study the radiative properties-the Lamb shift, Purcell decay rate and the spontaneous emission dynamics-of an artificial atom coupled to a long, multimode cavity formed by an array of Josephson junctions. Introducing a tunable coupling element between the atom and the array, we demonstrate that such a system can exhibit a crossover from a perturbative to non-perturbative regime of light-matter interaction as one strengthens the coupling between the atom and the Josephson junction array (JJA). As a consequence, the concept of spontaneous emission as the occupation of the local atomic site being governed by a single complex-valued exponent breaks down. This breakdown, we show, can be interpreted in terms of formation of hybrid atom-resonator modes with radiative losses that are non-trivially related to the effective coupling between individual modes. We develop a singular function expansion approach for the description of the open quantum system dynamics in such a multimode non-perturbative regime. This modal framework generalizes the normal mode description of quantum fields in a finite volume, incorporating exact radiative losses and incident quantum noise at the delimiting surface. Our results are pertinent to recent experiments with Josephson atoms coupled to high impedance Josephson junction arrays.

Chiral SQUID-metamaterial waveguide for circuit-QED

“…The Josephson-chain metamaterials, which inherit the advantages of Josephson junctions such as nonlinearity and tunability, have been widely employed for different quantum engineering tasks [50][51][52][53][54][55][56][57][58]. For example, many-body quantum optics in ultra-strong coupling regimes was successfully demonstrated in a Josephson chain platform by exploiting its high characteristic impedance [59].…”