%0 Journal Article
%T Dynamical polaron ansatz: a theoretical tool for the ultra-strong coupling regime of circuit QED
%A Guillermo D¨ªaz-Camacho
%A Alejandro Bermudez
%A Juan Jos¨¦ Garc¨ªa-Ripoll
%J Physics
%D 2015
%I arXiv
%X In this work we develop a semi-analytical variational ansatz to study the properties of few photon excitations interacting with a collection of quantum emitters in regimes that go beyond the rotating wave approximation. This method can be used to approximate both the static and dynamical properties of a superconducting qubit in an open transmission line, including the spontaneous emission spectrum and the resonances in scattering experiments. The approximations are quantitatively accurate for rather strong couplings, as shown by a direct comparison to Matrix-Product-State numerical methods, and provide also a good qualitative description for stronger couplings well beyond the Markovian regime.
%U http://arxiv.org/abs/1512.04244v1