AMO SEMINAR

Tuesday 18 August, 2015 at 14.15-14.45
Building 1520-732

Speaker: Kean Loon Lee

Title: Kinetics of two-component trapped condensates at finite temperature

Abstract:
A binary mixture of Bose-Einstein condensates can exhibit interesting phenomena, such as phase separation and nonlinear excitations. An important consideration is the collisional dynamics, which can be crucial in, e.g. damping of collective modes [1, 2] or growth of condensates [3, 4]. We have recently formulated [5, 6] an extended self-consistent kinetic model to study the non-equilibrium coupled dynamics of two interacting atomic Bose-Einstein condensates at finite temperature, where both components are partially-condensed. The condensates are described by dissipative Gross-Pitaevskii equations, coupled to quantum Boltzmann equations for the thermal atoms in a fully self-consistent manner through both the mean-field interactions as well as all possible collisional processes between the condensates and the thermal atoms.

Collision rates calculated based on equilibrium binary mixture in realistic experimental situations demonstrate the potential dominance of an energy-conserving exchange collision involving one condensate atom and one thermal atom from different components. This collisional exchange process could therefore be relevant when both components acquire condensate fractions, e.g. at the second-stage of sympathetic cooling, although the actual dynamics depends on such process in a more complicated manner. Our numerical analysis is based on realistic experimental mixtures of trapped 87Rb-41K and 87Rb-85Rb atoms near equilibrium, both in the miscible and immiscible regimes. By considering the collision rates near equilibrium, we discuss the extent to which the hydrodynamicity of the different mixtures can be controlled by the variations of temperature, trap frequencies and trap geometries. We also present early dynamical simulations on rethermalisation of binary mixtures and damping of collective oscillations.

[1] B. Jackson and E. Zaremba, PRL 87 100404 (2001)
[2] A. J. Allen, E. Zaremba, C. F. Barenghi, and N. P. Proukakis, PRA 87, 013630 (2013)
[3] M. J. Bijlsma, E. Zaremba, and H. T. C. Stoof, PRA 62, 063609 (2000)
[4] J. Märkle, A. J. Allen, P. Federsel, B. Jetter, A. Gänther, J. Fortágh, N. P. Proukakis, and T. E. Judd, PRA 90, 023614 (2014)
[5] M. J. Edmonds, K. L. Lee and N. P. Proukakis, PRA 91, 011602(R) (2015)
[6] M. J. Edmonds, K. L. Lee and N. P. Proukakis, arXiv: 1507.05078