Low energy excitations in 1D Fermi gases*

The quantum regime of ultracold fermions confined to one dimension (1D) is characterized by collective excitations, unlike the Fermi-liquid regime typically encountered in three dimensions. For example, in 1D, we find spin-density and charge-density waves that are linearly dispersing, rather than the Fermionic quasi-particles in 3D. We present the results of our experimental investigation of the system using a two-dimensional (2D) optical lattice to produce a 2D array of 1D tubes. Our previous investigations revealed several intriguing phenomena, including spin-charge separation in systems with repulsive interactions [1], the spin-incoherent Tomonaga-Luttinger liquid (TLL) [2], and the Luther-Emery regime, a gas confined in 1D with attractive interaction.

We extend these investigations by introducing a standing wave along the 1D tubes to realize the 1D Fermi-Hubbard model in the weak lattice limit. This opens a pathway to explore a new class of quantum systems. Using Bragg spectroscopy, we selectively excite low-energy spin and charge waves and measure the dynamic structure factor (DSF) for the spin and charge modes with various interaction strengths and signs. Bound states are characterized by RF spectroscopy. The results will be presented.

[1] R. Senaratne et al, Science 376, 1305-1308 (2022).

[2] D. Cavazos-Cavazos et al, Nature Communication 14, 3154 (2023).