Lamb-Shift Enhancement and Detection in Strongly Driven Superconducting Circuits

It is shown that strong driving of a quantum system substantially enhances the Lamb shift induced by broadband reservoirs, which are typical for solid-state devices. By varying drive parameters the impact of environmental vacuum fluctuations with continuous spectral distribution onto system observables can be tuned in a distinctive way. This provides experimentally feasible measurement schemes for the Lamb shift in superconducting circuits based on Cooper pair boxes, where it can be detected either in shifted dressed transition frequencies or in pumped charge currents.