Hotter condensates

Henry Krips

Abstract One of the features of modern physics is the extensive use of quantitative concepts to enrich qualitative concepts. For example a comparative qualitative judgement that A is hotter than B will be redescribed quantitatively by saying that the temperature value of A is greater than that of B. This quantitative language has much greater expressive power than the qualitative language it replaces. For example it enables sense to be made of such claims as ‘A is as much hotter than B as B is hotter than C’. For our purposes, however, the important feature of quantitative language is that it enables the development of the idea of a possible state.

Daniel S. Rokhsar

Tomasz Karpiuk, Benoît Grémaud, Christian Miniatura +1 more

We consider a simple experimental setup, based on a harmonic confinement, where a Bose-Einstein condensate and a thermal cloud of weakly interacting alkali-metal atoms are trapped in two different vessels connected by a narrow channel. Using the classical field approximation, we theoretically investigate the analog of the celebrated superfluid-helium fountain effect. We show that this thermomechanical effect might indeed be observed in this system. By analyzing the dynamics of the system, we are able to identify the superfluid and normal components of the flow as well as to distinguish the condensate fraction from the superfluid component. We show that the superfluid component can easily flow from the colder vessel to the hotter one while the normal component is practically blocked in the latter. In the long-time limit, the superfluid component exhibits periodic oscillations reminiscent of the ac Josephson effect obtained in superfluid weak-link experiments.

Shuai Peng, Haotian Liu, Jiaming Li +1 more

Abstract Evaporative cooling stands as the prevailing method for achieving ultracold temperatures in atomic systems. Current schemes of evaporation selectively remove the hotter atoms near the edge of the trap, as the hotter and colder atoms are distributed in different spatial regions of the trapping potential. However, a long-standing goal is to directly remove the higher momentum atoms, irrespective of their spatial distribution. For this purpose, we demonstrate collisional cooling for a 6Li Fermi gas through inelastic three-body recombination near a narrow Feshbach resonance. Such three-body recombination can induce either heating or cooling effects, and the decay of the quasi-bound Feshbach molecule stirs the hotter atoms away from the trapping potential. When the threshold energy of the Feshbach molecule exceeds the atom’s average kinetic energy of 3/2kBT, the cooling effect becomes more pronounced. Finally, we observe strong temperature dependence in this collisional cooling process, with greater efficiency achieved at lower temperatures.