Apparaît dans la collection : PRACQSYS 2018: Principles and Applications of Control in Quantum Systems

In this talk, I will present our implementation of ultra-strong light-matter coupling using a compact vacuum-gap transmon qubit design. Using a qubit whose capacitance is dominated by the coupling to the cavity it hangs above, we observe a vacuum Rabi splitting of 1.2 GHz and achieve ratios of g/ = 0.19, well into the ultra-strong coupling regime to a multimode electromagnetic cavity. Motivated by a desire to analyze our data quantitatively, we developed circuit-quantization model for the multimode ultra-strong regime in which we find a “natural” renormalization of the parameters of the bare quantum Rabi model as modes are added. With this formulation, we gain new insight into the convergence of the Lamb shift, and also how “quantum” the Lamb shift is itself in circuit QED and beyond.