In recent experiments we have realized the strong coupling limit of cavity quantum electrodynamics using superconducting circuits. In our approach, we use a Cooper pair box acting as an artificial atom coupled to a transmission line resonator forming a one-dimensional cavity. The strong coupling limit is reached as the vacuum Rabi frequency for the coupling of cavity photons to quantized excitations of the qubit exceeds the damping rates of both the cavity and the qubit. When the qubit is detuned from the cavity resonance frequency, there is still a large dispersive coupling of the qubit and the cavity, which can be used to perform a non-demolition measurement of the qubit state or the photon state of the cavity. I will discuss results using this measurement scheme to probe the coherence limits of the qubit, and to resolve the photon number state inside the cavity.
Yale University