Ramping fermions in optical lattices across a Feshbach resonance

TL;DR

This paper investigates ultracold Fermi gases in optical lattices near a Feshbach resonance, revealing enhanced three-body processes, finite temperature effects, and providing a new thermometry method, with implications for quantum simulation.

Contribution

It introduces a zero-temperature formalism for lattice Fermi gases, analyzes three-body process enhancement, and proposes a thermometry technique based on double occupancy.

Findings

Three-body processes are enhanced in lattices compared to continuum.

Current experiments are at higher temperatures than needed for quantum simulation.

Double occupancy relates to temperature, enabling thermometry in fermionic lattices.

Abstract

We study the properties of ultracold Fermi gases in a three-dimensional optical lattice when crossing a Feshbach resonance. By using a zero-temperature formalism, we show that three-body processes are enhanced in a lattice system in comparison to the continuum case. This poses one possible explanation for the short molecule lifetimes found when decreasing the magnetic field across a Feshbach resonance. Effects of finite temperatures on the molecule formation rates are also discussed by computing the fraction of double-occupied sites. Our results show that current experiments are performed at temperatures considerably higher than expected: lower temperatures are required for fermionic systems to be used to simulate quantum Hamiltonians. In addition, by relating the double occupancy of the lattice to the temperature, we provide a means for thermometry in fermionic lattice systems, previously not accessible experimentally. The effects of ramping a filled lowest band across a Feshbach resonance when increasing the magnetic field are also discussed: fermions are lifted into higher bands due to entanglement of Bloch states, in good agreement with recent experiments.