andreas.wallraff@yale.edu

We have realized an experiment in which we investigate the quantum dynamics of an electrical two-state system coupled to a single photon of a quantized electromagnetic field. We use a Cooper-pair box as a qubit and a superconducting resonator as a cavity.

We have performed experiments in which we have observed for the first time the quantum dynamics of a single Josephson vortex. Spectroscopically we have shown that the energy of a vortex in a potential well is quantized and that the vortex can tunnel through a potential barrier. These observations are important for the understanding of vortex properties at low temperatures in a wide range of systems such as superconductors, superfluids and atomic Bose condensates. They also have implications for performance of superconducting devices which may be limited by the dynamics of vortices.

We have spectroscopically studied the energy level structure in a macroscopic quantum nonlinear oscillator realized as a current-biased Josephson tunnel junction. Due to the strong nonlinearity of the oscillator, transitions between adjacent levels can be realized absorbing either a single photon or an arbitrary number of photons simultaneously. These effects are important in many solid state qubits.

Acoustic whispering gallery modes can be observed in St. Pauls cathedral in London. Josephson vortices moving at high velocities in annular superconducting tunnel junctions may excited electromagnetic whispering gallery modes by means of the Cherenkov effect. We have experimentally observed this effect for the first time.