Phenomenological theory of spinor Bose-Einstein condensates

A phenomenological model is proposed to describe the behavior of spinor Bose-Einstein condensates. In the absence of hyperfine spin-spin interactions, Bose-Einstein condensation leads to a spontaneous magnetization at the same transition temperature. This is the so-called Bose-Einstein ferromagnetism. Including the hyperfine spin interactions, the phase diagram of the spinor condensate in an optical trap is studied and the Gross-Pitaevskii equation is extended. The possibility of checking for the existence of the Bose-Einstein ferromagnetism experimentally is also discussed.Comment: 4 pages, 1 figure, extended discussions, added reference

Effects of dark energy on P-V criticality of charged AdS black holes

In this Letter, we investigate the effects of dark energy on $P-V$ criticality of charged AdS black holes by considering the case of the RN-AdS black holes surrounded by quintessence. By treating the cosmological constant as thermodynamic pressure, we study its thermodynamics in the extended phase space. It is shown that quintessence dark energy does not affect the existence of small/large black hole phase transition. For the case $\omega_q=-2/3$ we derive analytic expressions of critical physical quantities, while for cases $\omega_q\neq-2/3$ we appeal to numerical method for help. It is shown that quintessence dark energy affects the critical physical quantities near the critical point. Critical exponents are also calculated. They are exactly the same as those obtained before for arbitrary other AdS black holes, which implies that quintessence dark energy does not change the critical exponents.Comment: 13 pages, 2 figure

Dynamics of Two-Component Bose-Einstein Condensates Coupled with Environment

We investigate the dynamics of an open Bose-Einstein condensate system consisting of two hyperfine states of the same atomic species which are coupled by tunable Raman laser. It is already suggested that the detuning between the laser frequency and transition frequency affect significantly on the dynamics of the pure condensate. Here we show that the detuning effect is suppressed by noise and dissipation caused by the environment. The increase of coherence and purity are also displayed for specific parameters. As a verification to the lowest-order approximation we derive the hierarchy of motion equations in the second-order approximation. It turns out that the former one can describe the dynamical evolution qualitatively for weak noise and dissipation and quantitatively for strong noise and dissipation.Comment: 7 pages,8 figure

Phase-imprint induced domain formations and spin dynamics in spinor condensates

We demonstrate that certain domain structures can be created both in ferro- and antiferro-magnetic spinor condensates if the initial phase is spatially modulated. Meanwhile, spin dynamics of the condensate with modulated phases exhibits exotic features in comparison with those of a condensate with a uniform phase. We expect that these phenomena could be observed experimentally using a phase-imprinting method.Comment: 5 pages, 5 figures, to appear in Phys. Rev.