arXiv subjects
Publications and source records attributed to Christian Schori.
We report on the realization of a quantum degenerate atomic Fermi gas in an optical lattice. Fermi surfaces of noninteracting fermions are studied in a three-dimensional lattice. Using a Feshbach resonance, we observe a coupling of the Bloch bands in the strongly interacting regime.
We prepare a Bose-Einstein condensed gas in a three-dimensional optical lattice and study the excitation spectrum of the superfluid phase for different interaction strengths. We probe the response of the system by modulating the depth of the optical lattice along one axis. The interactions can be controlled independently by varying the tunnel coupling along the other two lattice axes. In the weakly interacting regime we observe a small susceptibility of the superfluid to excitations, while for stronger interactions an unexpected resonance appears in the excitation spectrum. In addition we measure the coherent fraction of the atomic gas, which determines the depletion of the condensate.
We report on the study of the momentum distribution of a one-dimensional Bose gas in an optical lattice. From the momentum distribution we extract the condensed fraction of the gas and thereby measure the depletion of the condensate and compare it with a theorical estimate. We have measured the coherence length of the gas for systems with average occupation $\bar{n}>1$ and $\bar{n}<1$ per lattice site.
We study one-dimensional trapped Bose gases in the strongly interacting regime. The systems are created in an optical lattice and are subject to a longitudinal periodic potential. Bragg spectroscopy enables us to investigate the excitation spectrum of the one-dimensional gas in different regimes. In the superfluid phase a broad continuum of excitations is observed which calls for an interpretation beyond the Bogoliubov spectrum taking into account the effect of quantum depletion. In the Mott insulating phase a discrete spectrum is measured. The excitation spectra of both phases are compared to the three-dimensional situation and to the crossover regime from one to three dimensions. The coherence length and coherent fraction of the gas in all configurations are measured quantitatively. We observe signatures for increased fluctuations which are characteristic for 1D systems. Furthermore, ceasing collective oscillations near the transition to the Mott insulator phase are found.
We report the observation of non-classical quantum correlations of continuous light variables from a novel type of source. It is a frequency non-degenerate optical parametric oscillator below threshold, where signal and idler fields are separated by 740MHz corresponding to two free spectrum ranges of the parametric oscillator cavity. The degree of entanglement observed, - 3.8 dB, is the highest to-date for a narrowband tunable source suitable for atomic quantum memory and other applications in atomic physics. Finally we use the latter to visualize the Einstein-Podolsky-Rosen paradox.