Fermi Gases In The Two-Dimensional To Quasi-Two-Dimensional Crossover

We smoothly tune the dimensionality of pancake-shaped Li-6 Fermi gas clouds from quasi-two-dimensional to two-dimensional (2D) to measure radio-frequency spectra and cloud profiles in both regimes. In the quasi-2D case, where E-F/h nu(z) similar or equal to 1, with E-F the Fermi energy and h nu(z) the harmonic oscillator energy in the tightly confined direction, we confirm that the radio-frequency spectra strongly disagree with 2D mean-field theory. Then we tune to the 2D regime, E-F << h nu(z), where the measured radio-frequency spectra are in very good agreement with 2D mean-field theory. Nevertheless, the measured cloud profiles strongly disagree, confirming predictions that a beyond mean-field approach is required throughout the 2D to quasi-2D crossover.