Abstract
The low temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. Here we first present a theoretical model that describes the dynamic competition between two-body evaporation and three-body re-combination in a harmonically trapped unitary atomic gas above the condensation temperature. We identify a universal magic trap depth where, within some parameter range, evaporative cooling is balanced by recombination heating and the gas temperature stays constant. Our model is developed for the usual three-dimensional evaporation regime as well as the 2D evaporation case. Experiments performed with unitary 133 Cs and 7 Li atoms fully support our predictions and enable quantitative measurements of the 3-body recombination rate in the low temperature domain. In particular, we measure for the first time the Efimov inelasticity parameter $\eta$ * = 0.098(7) for the 47.8-G d-wave Feshbach resonance in 133 Cs. Combined 133 Cs and 7 Li experimental data allow investigations of loss dynamics over two orders of magnitude in temperature and four orders of magnitude in three-body loss. We confirm the 1/T 2 temperature universality law up to the constant $\eta$ *.
Highlights
Interacting Bose systems realized in ultracold atomic gases are attracting growing attention thanks to being among the most fundamental systems in nature and among the least studied
We show below that the additional dynamics come from the two-body evaporation due to the finite trap depth
We have examined the coupled time dynamics of atom number and temperature of the 3D harmonically trapped unitary Bose gas in the nondegenerate regime
Summary
Interacting Bose systems realized in ultracold atomic gases are attracting growing attention thanks to being among the most fundamental systems in nature and among the least studied. Three-body recombination rates in the nondegenerate regime have been measured in two different species, 7Li [15] and 39K [16], and they clarified the temperature dependence of the unitary Bose gas lifetime In another experiment, fast and nonadiabatic projection of the BEC on the regime of unitarity revealed the establishment of thermal quasiequilibrium on a time scale faster than inelastic losses [17]. We find the existence of a “magic” value for the trap-depth-over-temperature ratio, where residual evaporation compensates for three-body loss heating and maintains the gas temperature constant within some range of parameters Comparing measurements in these two atomic species, we find the dynamics to be universal; i.e., in both systems, the three-body loss rate is found to scale universally with temperature. Excellent agreement between theory and experiment confirms that the dynamic evolution of the unitary Bose gas above the condensation temperature can be well modeled by the combination of two- and threebody interaction processes
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