Two-point phase correlations of a one-dimensional bosonic Josephson junction.

We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows us to measure the coupling strength and temperature and hence a full characterization of the system.

Cavity QED with magnetically coupled collective spin states.

We report strong coupling between an ensemble of nitrogen-vacancy center electron spins in diamond and a superconducting microwave coplanar waveguide resonator. The characteristic scaling of the collective coupling strength with the square root of the number of emitters is observed directly. Additionally, we measure hyperfine coupling to (13)C nuclear spins, which is a first step towards a nuclear ensemble quantum memory. Using the dispersive shift of the cavity resonance frequency, we measure the relaxation time of the NV center at millikelvin temperatures in a nondestructive way.

Strong magnetic coupling of an ultracold gas to a superconducting waveguide cavity.

Placing an ensemble of 10;{6} ultracold atoms in the near field of a superconducting coplanar waveguide resonator with a quality factor Q approximately 10;{6}, one can achieve strong coupling between a single microwave photon in the coplanar waveguide resonator and a collective hyperfine qubit state in the ensemble with g_{eff}/2pi approximately 40 kHz larger than the cavity linewidth of kappa/2pi approximately 7 kHz. Integrated on an atomchip, such a system constitutes a hybrid quantum device, which also can be used to interconnect solid-state and atomic qubits, study and control atomic motion via the microwave field, observe microwave superradiance, build an integrated micromaser, or even cool the resonator field via the atoms.