Sahel Ashhab, Qatar Environment and Energy Research Institute, Qatar Foundation
Cavity QED in the ultrastrong-coupling regime & Landau-Zaner-Stückelberg interfereometry
Superconducting circuits are allowing experimentalists to explore physical systems in parameter regimes that were not accessible using other systems in the past. In this talk, I will cover two problems that are representative of this situation. First, I will talk about cavity QED systems in the case where the coupling strength is comparable to the atomic and cavity frequencies. In this regime, the ground state of the system can become a highly correlated atom-cavity state. We analyze the behavior of the ground state as the different parameters are varied, and we investigate the transitions between different types of ground states. In the second part of the talk, I will discuss the problem of a qubit that is subjected to large-amplitude driving, such that it undergoes a periodic sequence of Landau-Zener transitions. We analyze the resonance conditions and the dynamics of the qubit in this situation. In particular, we find that there are two qualitatively different types of resonance behavior occuring in the limits of slow and fast Landau-Zener passage.