There is a growing interest in the relation between Bose-Einstein condensation (BEC) and the superfluidity. A Bose system confined in random media such as porous glass is suitable for studying this relation because BEC and superfluidity can be suppressed and controlled in such a disordered environment. However, it is not clear how this relation is affected by disorder and there are few theoretical studies that can be quantitatively tested by experiment. In this work we develop a dilute Bose gas model with a random potential that takes into account the pore-size dependence of porous glass. Then we compare our model with the measured low-temperature specific heat, condensate density, and superfluid density of
4He in Vycor glass. This comparison uses no free parameters. We predict phenomena at low temperatures: First, the random potential causes a T-linear specific heat instead of the
T3 dependence that is usually caused by phonons. Second, the BEC can remain even when the superfluidity disappears at low densities. Third, the system makes a reentrant transition at low densities; that is, the superfluid phase changes to the normal phase again as the temperature is reduced. This reentrant transition is more likely to be observed when the strength of the random potential is increased.
Abstract Bose–Einstein condensates (BECs) are starting to play a role in quantum information processing, and there is a need to better understand the dynamical processes at play in the condensates. In this paper, we review recent work on a kinetic model for ultra-low temperature dilute Bose–Einstein condensates that gives correct behavior for first and second sound speeds at very low temperature, and gives explicit expressions and values for decay processes. The predictions of the theory are in agreement with experiment. The method explicitly computes the hydrodynamic modes of the condensate using a method that has also been used to describe decay processes in noble gas mixtures, and thereby opens the way for future analysis of decay processes in BEC mixtures.