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arXiv:cond-mat/0309004

Competition between phase coherence and correlation in a mixture of Bose-Einstein condensates

Ma, Hong, Tao Pang

Published Aug 29, 2003• 0 citations
arXivHTMLPDF

Abstract

Two-species hard-core bosons trapped in a three-dimensional isotropic harmonic potential are studied with the path-integral quantum Monte Carlo simulation. The double condensates show two distinct structures depending on how the external potentials are set. Contrary to the mean-field results, we find that the heavier particles form an outer shell under an identical external potential whereas the lighter particles form an outer shell under the equal energy spacing condition. Phase separations in both the spatial and energy spaces are observed. We provide physical interpretations of these phase separations and suggest future experiment to confirm these findings.

DOI
10.48550/arxiv.cond-mat/0309004

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This thesis investigates bosonic mixtures in ultra-cold atom systems. We mainly focus on mixtures of two bosonic twin-species trapped in optical lattices, paying particular attention to the properties of spatial separation. The study is carried out by means of the path-integral quantum Monte Carlo by the two-worm algorithm and by analytical calculations where the complexity of the system allows it. The mixture is trapped in a square optical lattice at different filling and temperature conditions. We explore the ground-state phase diagram showing that various quantum phases can arise depending on the interplay between intra- and inter-species interactions. Demixed phases, characterized by spatial separation of the two species, are studied in details determining under which conditions they can be stabilized. The influence of temperature, filling factor and harmonic trap on phase separation is also investigated. An interesting dependence of the degree of demixing from temperature has been found, suggesting new ways to measure the temperature of a two-component bosonic mixture. We also study spatial phase separation in the simple case of a two-component mixture in a double-well potential both numerically and by means of the Bogoliubov approximaton. We show that even in this simple case the main features of the mixing/ demixing phase transitions are observed, and that the transition is characterized by a spectral collapse of the energy eigenvalues reflecting the dramatic change of algebraic structure of the model.
The ground-state properties of a system with a small number of interacting bosons over a wide range of densities are investigated. The system is confined in a two-dimensional isotropic harmonic trap, where the interaction between bosons is treated as a hard-core potential. By using variational Monte Carlo method, we diagonalize the one-body density matrix of the system to obtain the ground-state energy, condensate wavefunction and the condensate fraction. We find that in the dilute limit the depletion of central condensate in the 2D system is larger than in a 3D system for the same interaction strength; however as the density increases, the depletion at the centre of 2D trap will be equal to or even lower than that at the centre of 3D trap, which is in agreement with the anticipated in Thomas–Fermi approximation. In addition, in the 2D system the total condensate depletion is still larger than in a 3D system for the same scattering length.