Measurement of the Dynamical Structure Factor of a 1D Interacting Fermi Gas

We present measurements of the dynamical structure factor S(q,omega) of an interacting one-dimensional Fermi gas for small excitation energies. We use the two lowest hyperfine levels of the Li-6 atom to form a pseudospin-1/2 system whose s-wave interactions are tunable via a Feshbach resonance. The atoms are confined to one dimension by a two-dimensional optical lattice. Bragg spectroscopy is used to measure a response of the gas to density (charge) mode excitations at a momentum q and frequency omega, as a function of the interaction strength. The spectrum is obtained by varying omega, while the angle between two laser beams determines q, which is fixed to be less than the Fermi momentum k(F). The measurements agree well with Tomonaga-Luttinger theory.