报告摘要：Nanostructured superconductors with Josephson junctions behave
under proper conditions as artificial atoms. They are currently one of
the main candidates for the implementation of a quantum computer and a
testbed for fundamental studies in quantum mechanics. Among the various
types of superconducting quantum systems, flux qubits are distinguished
through a combination of large level anharnmonicity and strong coupling
to electromagnetic fields. Therefore, they are an ideal system to study
strong interaction effects between a two-level system and the
electromagnetic field.

In the first part of the talk, I will discuss the interaction between a
flux qubit and a strong classical field. The dynamics is well described
by Floquet states, which are quasistationary solutions of the
Schrodinger equation with a time-periodic Hamiltonian. We directly
observe Floquet states of the artificial atom driven with short resonant
pulses and a field amplitude which reaches more than twice the atomic
frequency. The dynamics of the driven system depends on the pulse rise
fall/times, in agreement with the adiabatic conditions in the Floquet
picture. These results have applications to the optimal control of
quantum systems. I will discuss how fast and high-fidelity single-qubit
unitaries can be implemented in the strong driving regime.

In the second part of the talk, I will present our recent work on the
investigation of strong coupling between a flux qubit and a
one-dimensional waveguide, in a regime where the coupling is comparable
to and even exceeds the atomic frequency.