Probing coherence properties of strongly interacting Bose gases

This thesis reports on experiments studying the coherence properties of strongly interacting homogeneous gases of bosonic lithium dimers confined to two dimensions. The main results of these studies are first measurements of the momentum distribution and the density-density correlation function after time of flight. The momentum distribution is measured via a matter wave focusing technique where the momentum space is mapped to real space by letting the gas expand into a harmonic potential. We observe a fast depopulation of the low-momentum modes for prolonged hold times in an optical dipole trap and extract the temperature from the high-momentum modes. The depopulation occurs with only minor increase in measured temperature, indicating that a non-equilibrium description might be required. Additionally, we present how the phase correlation function can be obtained from the momentum distribution and discuss the influence of finite size effects. Properties of the phase correlation function are inferred from the measurement of the density-density correlation function after short time of flight. During expansion, the in situ phase fluctuations of the gas transform into density fluctuations and thus produce an observable density pattern. By fitting the extracted density-density correlation function with theoretical predictions, the scaling exponent of the phase correlation function can be obtained if a power law decay is assumed. We measure the scaling exponent for extended hold time in an optical dipole trap and observe a downward trend. However this trend of the scaling exponent is inconsistent with the behavior of the high-momentum modes, which indicate constant or slightly increasing temperature. We discuss the numerical analysis and possible issues in detail and arrive at the conclusion that non-equilibrium effects likely render the employed theoretical framework inadequate.