Extreme tunability of interactions in a $^7$Li Bose-Einstein condensate

TL;DR

This paper demonstrates precise control over the interaction strength in a 7Li Bose-Einstein condensate using a Feshbach resonance, covering a wide range from attractive to strongly repulsive interactions, and observes magnetic dipole effects.

Contribution

It reports the first extensive tuning of scattering length in a 7Li BEC over seven decades, including near-zero interactions, and detects magnetic dipole interactions.

Findings

Scattering length tuned over 7 decades from attractive to repulsive.

Zero-crossing of scattering length determined at 0.01 Bohr radii.

Evidence of magnetic dipole interactions in different trap geometries.

Abstract

We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of 7Li in the |F = 1, m_F = 1> state. Using the spatial extent of the trapped condensate we extract a over a range spanning 7 decades from small attractive interactions to extremely strong repulsive interactions. The shallow zero-crossing in the wing of the Feshbach resonance enables the determination of a as small as 0.01 Bohr radii. In this regime, evidence of the weak anisotropic magnetic dipole interaction is obtained by comparison with different trap geometries.