Measurement of the Dynamic Structure Factor of a Strongly Interacting 1D Fermi Gas*

An interacting Fermi gas in one dimension (1D) cannot be explained by the familiar Landau Fermi liquid theory since excitations are collective, rather than quasi-particle excitations. Instead, such a system can be described by Tomonaga-Luttinger liquid (TTL) theory, where excitations near the Fermi surface are characterized by a linear, sound-like spectrum having different speeds for spin and charge waves. We present measurements of the dynamical structure factor $S(q,\omega)$ of an interacting 1D Fermi gas. We confine a spin-1/2 system of $^6$Li atoms to 1D by using a 2D optical lattice. Bragg spectroscopy is used to measure the response of the gas to density ("charge") mode excitations at momentum $q$ and frequency $\omega$. By fixing $q$ at $q_0$ and varying $\omega$, we obtain the spectrum $S(q_0, \omega)$. We vary the strength of the repulsive interactions using a Feshbach resonance.