Universal Loss Dynamics in a Unitary Bose Gas

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 $\eta$ *

Dynamical formation of the unitary Bose gas

“…However, over a wider range of atomic densities, preliminary loss-rate measurements [25] and theoretical results [24] indicate a log-periodic oscillation of the loss-rate with a density period set by the Efimov spacing e 3π/s0 ≈ 22.7 3 where s 0 ≈ 1.00624 is a universal constant for three identical bosons [10]. These results parallel oscillatory loss-rate predictions in the nondegenerate regime [26].…”

Universal few-body physics and cluster formation

“…As is discussed in greater de-tail in (Sykes et al, 2014), one obtains somewhat poorer quantitative agreement but still the correct order of magnitude for the loss rate at unitarity by replacing the value of a in the universal 3-body loss rate formulas by 1/K as defined above in terms of the average density in the gas. Other experimental studies of the unitary Bose gas that have focused on the three-body loss rate include (Eismann et al, 2016;Fletcher et al, 2013;Rem et al, 2013). And another intriguing "universality limit" where the scattering length is no longer a relevant length scale is the opposite limit a ≈ 0, recently explored experimentally with some phenomenological conjectures in (Shotan et al, 2014).…”

Few-body physics in resonantly interacting ultracold quantum gases

“…Along with the recent theoretical and experimental progress in the exploration of the collective behavior of ultracold quantum gases, the relevance of few-body physics, i.e., the physics of systems with three or more particles, has increasingly been recognized for its fundamental importance in determining the stability and dynamics of ultracold gases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The key ingredient that sets apart ultracold gases from most other physical systems is that the strength of the interatomic interactions can be controlled.…”