Stability of a unitary Bose gas

TL;DR

This paper investigates the stability and loss mechanisms of a thermal $^{39}$K Bose gas at unitarity, revealing species-specific effects that influence three- and four-body decay rates, and highlighting $^{39}$K's suitability for many-body physics studies.

Contribution

It provides experimental measurements of loss rates and scaling laws at unitarity for $^{39}$K, demonstrating deviations from universal theory due to Efimov physics.

Findings

Three-body loss coefficient at unitarity is lower than the universal bound.

Significant four-body decay observed for negative scattering length away from unitarity.

Species-specific Efimov physics reduces three-body losses, enhancing $^{39}$K's stability.

Abstract

We study the stability of a thermal $^{39}$K Bose gas across a broad Feshbach resonance, focusing on the unitary regime, where the scattering length $a$ exceeds the thermal wavelength $\lambda$. We measure the general scaling laws relating the particle-loss and heating rates to the temperature, scattering length, and atom number. Both at unitarity and for positive $a \ll \lambda$ we find agreement with three-body theory. However, for $a<0$ and away from unitarity, we observe significant four-body decay. At unitarity, the three-body loss coefficient, $L_3 \propto \lambda^4$, is three times lower than the universal theoretical upper bound. This reduction is a consequence of species-specific Efimov physics and makes $^{39}$K particularly promising for studies of many-body physics in a unitary Bose gas.