Observation of collectivity enhanced magnetoassociation of $^6$Li in the quantum degenerate regime

TL;DR

This study demonstrates that many-body coherence enhances the magnetoassociation of $^6$Li atoms near quantum degeneracy, revealing deviations from two-body Landau-Zener predictions and highlighting the importance of collective effects in molecule formation.

Contribution

The paper introduces a theoretical and experimental investigation of many-body effects on atom-molecule coupling during Feshbach association in a degenerate Fermi gas, showing enhanced coupling due to collectivity.

Findings

Atom-molecule coupling increases near quantum degeneracy.

Nonlinear magnetic field ramps can improve association efficiency.

Theoretical model agrees qualitatively with experimental data.

Abstract

The association process of Feshbach molecules is well described by a Landau-Zener (LZ) transition above the Fermi temperature, such that two-body physics dominates the dynamics. However, using $^6$Li atoms and the associated Feshbach resonance at $B_r=834.1$ G, we observe an enhancement of the atom-molecule coupling as the fermionic atoms reach degeneracy, demonstrating the importance of many-body coherence not captured by the conventional LZ model. In the experiment, we apply a linear association ramp ranging from adiabatic to non-equilibrium molecule association for various temperatures. We develop a theoretical model that explains the temperature dependence of the atom-molecule coupling. Furthermore, we characterize this dependence experimentally and extract the atom-molecule coupling coefficient as a function of temperature, finding qualitative agreement between our model and experimental results. In addition, we simulate the dynamics of molecular association during a nonlinear field ramp. We find that, in the non-equilibrium regime, molecular association efficiency can be enhanced by sweeping the magnetic field cubically with time. Accurate measurement of the atom-molecule coupling coefficient is important for both theoretical and experimental studies of molecular association and many-body collective dynamics.