Measurement of inelastic losses in a sample of ultracold Rb-85

TL;DR

This paper investigates inelastic collision losses in ultracold Rb-85 atoms near a Feshbach resonance, revealing a new loss feature at 219.9 G and demonstrating advanced sympathetic cooling techniques.

Contribution

It reports the first observation of a narrow inelastic loss feature at 219.9 G in ultracold Rb-85 and details an improved sympathetic cooling method for Rb-85 using Rb-87.

Findings

Observed a new loss feature at 219.9 G with a width of 0.28 G.

Demonstrated three orders of magnitude increase in phase space density of Rb-85.

Identified the loss feature as a narrow Feshbach resonance predicted by theory.

Abstract

We report on the observation and characterisation of an inelastic loss feature in collisions between ultracold Rb-85 |F=2, m_F=-2> atoms at a magnetic field of 220 G. Our apparatus creates ultracold Rb-85 clouds by sympathetic cooling with a Rb-87 reservoir, and can produce pure Rb-87 condensates of 10^6 atoms by a combination of evaporative cooling in a quadrupole-Ioffe magnetic trap and further evaporation in a weak, large-volume optical dipole trap. By combining Rb-85 and Rb-87 atoms collected in a dual-species magneto-optical trap and selectively evaporating the heavier isotope, we demonstrate strong sympathetic cooling of the Rb-85 cloud, increasing its phase space density by three orders of magnitude with no detectable loss in number. We have used ultracold samples created in this way to observe the variation of inelastic loss in ultracold Rb-85 as a function of magnetic field near the 155 G Feshbach resonance. We have also measured a previously unobserved loss feature at 219.9(1) G with a width of 0.28(6) G, which we associate with a narrow Feshbach resonance predicted by theory.