Abstract
The effects of miscibility in interacting two-component classical fluids are relevant in a broad range of daily applications. When considering quantum systems, two-component Bose–Einstein condensates provide a well-controlled platform where the miscible–immiscible phase transition can be completely characterized. In homogeneous systems, this phase transition is governed only by the competition between intra- and inter-species interactions. However, in more conventional experiments dealing with trapped gases, the pressure of the confinement increases the role of the kinetic energy and makes the system more miscible. In the most general case, the miscibility phase diagram of unbalanced mixtures of different atomic species is strongly modified by the atom number ratio and the different gravitational sags. Here, we numerically investigate the ground-state of a 23Na–39K quantum mixture for different interaction strengths and atom number ratios considering realistic experimental parameters. Defining the spatial overlap between the resulting atomic clouds, we construct the phase diagram of the miscibility transition which could be directly measured in real experiments.
Highlights
Mixtures of quantum fluids such as superfluid 3 He-4 He [1,2,3,4] and atomic Bose–Einstein condensates (BECs) [5,6,7,8,9,10,11,12,13,14] exhibit different miscibility regimes as a result of the competition between intra- and interspecies interactions between its components
New phase transitions give rise to a much more complex phase diagram than the simple extension of the superfluid to Mott insulator transition [15,16]; polaron physics can be explored with large imbalanced mixtures [17,18]; and the recently observed self-stabilized quantum droplets with liquid-like behaviour can be produced when beyond mean-field effects became dominant [19,20,21,22]
We explore the effect of changing the number of atoms of the minority species (39 K), thereby changing the atom number ratio η, and calculating the spatial overlap between the atomic clouds as a quantity able to characterize the change in the miscibility regime of the system
Summary
Einstein condensates (BECs) [5,6,7,8,9,10,11,12,13,14] exhibit different miscibility regimes as a result of the competition between intra- and interspecies interactions between its components. We perform numerical simulations of the ground-state of a two-component quantum mixture of 23 Na and 39 K atoms for different interaction strengths, according to the relevant Feshbach resonances for magnetic fields in the range of 95–117 G [14,39], in order to show the realistic miscibility regimes accessible in the experimental setup being developed in our laboratory [40] in the presence of gravity. The numerical simulations are performed at zero temperature, which satisfactorily reproduces the experimental results for the case of strongly degenerate atomic mixtures [41], theoretical works at finite temperature have shown a change of the miscibility condition of the system favoring phase separation [42,43,44].
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