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arXiv:2408.00737 · Physical Review A

Emergent s -wave interactions in orbitally active quasi-two-dimensional Fermi gases

Colin J. Dale, K. G. S. Xie, Kiera Pond Grehan, Shizhong Zhang, Jeff Maki, Joseph H. Thywissen

Published Nov 15, 2024• 5 citations
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Abstract

The authors prepare a quasi-two-dimensional spin-polarized Fermi gas with orbital excitations and p-wave interactions enabled by a Feshbach resonance. Radio-frequency spectroscopy indicates $s$-wave scattering symmetry in the plane, demonstrating how gapped orbital degrees of freedom can be used to control scattering symmetry in strongly confined ultracold gases.

DOI
10.1103/physreva.110.l051302

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The authors prepare a quasi-two-dimensional spin-polarized Fermi gas with orbital excitations and p-wave interactions enabled by a Feshbach resonance. Radio-frequency spectroscopy indicates sss-wave scattering symmetry in the plane, demonstrating how gapped orbital degrees of freedom can be used to control scattering symmetry in strongly confined ultracold gases.
Low-dimensional ultracold gases are created in the laboratory by confining three-dimensional (3D) gases inside highly anisotropic trapping potentials. Such trap geometries not only provide access to simulating 1D and 2D physics, but also can be used to study how the character of excitations cross over to three dimensions at higher energy. In this work we study the signature in radio-frequency (rf) spectroscopy for both the 1D-to-3D and the 2D-to-3D crossovers, in spin-polarized Fermi gases. We solve the two-body scattering TTT matrix in the presence of strong harmonic confinement and use it to evaluate both the high-frequency rf transfer rate and the two-body bound-state energies. These general expressions are then compared both to the low-dimensional limit and to the 3D limit. We find that in order to understand the dimensional crossover for spin-polarized Fermi gases with ppp-wave interactions, one needs to take into account an emergent sss-wave interaction.
We investigate the properties of a spin-orbit coupled quasi-two-dimensional Fermi gas with tunable sss-wave interaction between the two spin species. By analyzing the two-body bound state, we find that the population of the excited states in the tightly confined axial direction can be significant when the two-body binding energy becomes comparable to or exceeds the axial confinement. Since the Rashba spin-orbit coupling that we study here tends to enhance the two-body binding energy, this effect can become prominent at unitarity or even on the BCS side of the Feshbach resonance. To study the impact of these excited modes along the third dimension, we adopt an effective two-dimensional Hamiltonian in the form of a two-channel model, where the dressed molecules in the closed channel consist of the conventional Feshbach molecules as well as the excited states occupation in the axial direction. With properly renormalized interactions between atoms and dressed molecules, we find that both the density distribution and the phase structure in the trap can be significantly modified near a wide Feshbach resonance. In particular, the stability region of the topological superfluid phase is increased. Our findings provide a proper description for a quasi-two-dimensional Fermi gas under spin-orbit coupling, and are helpful for the experimental search for the topological superfluid phase in ultracold Fermi gases.
We study a spin-polarized degenerate Fermi gas interacting via a p-wave Feshbach resonance in an optical lattice. The strong confinement available in this system allows us to realize one- and two-dimensional gases and, therefore, to restrict the asymptotic scattering states of atomic collisions. When aligning the atomic spins along (or perpendicular to) the axis of motion in a one-dimensional gas, scattering into channels with the projection of the angular momentum of /m/ = 1 (or m = 0) can be inhibited. In two and three dimensions, we observe the doublet structure of the p-wave Feshbach resonance. For both the one-dimensional and the two-dimensional gases, we find a shift of the position of the resonance with increasing confinement due to the change in collisional energy. In a three-dimensional optical lattice, the losses on the Feshbach resonance are completely suppressed.
We report on the experimental observation of a strongly interacting gas of ultracold two-electron fermions with an orbital degree of freedom and magnetically tunable interactions.This realization has been enabled by the demonstration of a novel kind of Feshbach resonance occurring in the scattering of two 173 Yb atoms in different nuclear and electronic states.The strongly interacting regime at resonance is evidenced by the observation of anisotropic hydrodynamic expansion of the two-orbital Fermi gas.These results pave the way towards the realization of new quantum states of matter with strongly correlated fermions with an orbital degree of freedom.
Ultracold gases of interacting spin-orbit-coupled fermions are predicted to display exotic phenomena such as topological superfluidity and its associated Majorana fermions. Here, we experimentally demonstrate a route to strongly interacting single-component atomic Fermi gases by combining an s-wave Feshbach resonance (giving strong interactions) and spin-orbit coupling (creating an effective p-wave channel). We identify the Feshbach resonance by its associated atomic loss feature and show that, in agreement with our single-channel scattering model, this feature is preserved and shifted as a function of the spin-orbit-coupling parameters.