Excitation in Ultracold Fermi Gases

Professor Chris Vale

Centre for Quantum and Optical Science, Swinburne University of Technology

Gases of neutral Fermi atoms cooled to nanoKelvin temperatures provide a versatile testbed for developing a quantitative understanding of many-body phenomena in macroscopic quantum systems. In this talk I will present measurements of the excitation spectra of strongly interacting Fermi gases at both low and high momentum using focused beam Bragg spectroscopy. At low momentum, below the superfluid transition temperature, the Goldstone mode or Bogoliubov-Anderson phonon is the dominant low energy excitation. For energies larger than twice the pairing gap, the single-particle continuum becomes visible. The frequencies of the phonon mode and the onset of single-particle excitations provide direct measures of the speed of sound and pairing gap, respectively. At high momentum, focused beam Bragg spectroscopy allows the determination of Tan’s universal contact parameter and the internal energy via the application of sum-rules. These allow us to map the temperature dependence of the contact and energy for gases with resonantly enhanced elastic collisions.

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