Accelerating evaporative cooling of a strongly interacting Fermi gas by tilting the optical trap with a magnetic field gradient

TL;DR

This paper introduces a rapid cooling method for strongly interacting Fermi gases using a magnetic-field-gradient-induced tilt of the optical trap, achieving superfluid temperatures faster than traditional methods.

Contribution

The authors develop a novel cooling technique that combines optical trap depth reduction with magnetic-field-gradient tilting to accelerate cooling of a Fermi gas into the superfluid regime.

Findings

Achieved cooling of $^{6}$Li Fermi gas to $T/T_F=0.16$ in ~25 ms.

Enhanced cooling rate by applying magnetic-field gradient at half the Fermi temperature.

Method enables rapid access to superfluid regime in strongly interacting Fermi gases.

Abstract

We present a rapid evaporative cooling scheme for a strongly interacting $^{6}\mathrm{Li}$ Fermi gas in an optical dipole trap. The method uses a magnetic-field-gradient--induced tilt of the trapping potential to accelerate cooling in the unitarity-limited regime. In evaporation based only on lowering the optical trap depth, the unitarity-limited scattering cross section can support runaway cooling; however, the cooling rate slows around $T/T_F \simeq 0.5$, and the runaway behavior is no longer maintained. We improve on this approach by applying a magnetic-field gradient when the gas temperature reaches about half the Fermi temperature. The induced tilt opens an escape channel for energetic atoms while keeping the trap frequencies nearly unchanged. This modification increases the cooling speed and cools the gas below the superfluid transition temperature, reaching $T/T_F = 0.16$ on a timescale of $\sim 25\,\mathrm{ms}$. Our results provide a simple and robust route for rapidly cooling a strongly interacting Fermi gas into the superfluid regime, facilitating studies of the physics of unitary Fermi superfluids.