Dipolar Fermi gases in anisotropic traps

TL;DR

This paper develops a detailed theoretical framework for dipolar Fermi gases in anisotropic traps, analyzing their static properties, excitations, and expansion dynamics, with implications for experiments on strongly dipolar quantum gases.

Contribution

It extends previous models to general anisotropic traps and explores static solutions, excitations, and expansion behavior of dipolar Fermi gases.

Findings

Momentum distribution remains cylinder symmetric despite trap asymmetry.

Real-space aspect ratios invert during expansion.

Identifies low-lying hydrodynamic modes including quadrupole and monopole.

Abstract

The quest for quantum degenerate Fermi gases interacting through the anisotropic and long-range dipole-dipole interaction is an exciting and fast developing branch within the cold-atoms research program. Recent experimental progress in trapping, cooling, and controlling polar molecules with large electric dipole moments has, therefore, motivated much theoretical effort. In a recent letter, we have briefly discussed the application of a variational time-dependent Hartree-Fock approach to study theoretically both the static and the dynamic properties of such a system in a cylinder-symmetric harmonic trap. We focused on the hydrodynamic regime, where collisions assure the equilibrium locally. Here, we present a detailed theory, extended to encompass the general case of a harmonic trap geometry without any symmetry. After deriving the equations of motion for the gas, we explore their static solutions to investigate key properties like the aspect ratios in both real and momentum space as well as the stability diagram. We find that, despite the lack of symmetry of the trap, the momentum distribution remains cylinder symmetric. The equations of motion are then used to study the low-lying hydrodynamic excitations, where, apart from the quadrupole and monopole modes, also the radial quadrupole mode is investigated. Furthermore, we study the time-of-flight dynamics as it represents an important diagnostic tool for quantum gases. We find that the real-space aspect ratios are inverted during the expansion, while the one in momentum space becomes asymptotically unity. In addition, anisotropic features of the dipole-dipole interaction are discussed in detail. These results could be particularly useful for future investigations of strongly dipolar heteronuclear polar molecules deep in the quantum degenerate regime.