A mixture of the multicomponent Bose-Einstein condensate is considered, where each component moves with its own velocity. As a result of the relative motion, the mixture stratifies when the relative velocity reaches a critical value. Stability conditions for a binary moving mixture are derived and the critical velocity is found.
We investigate the dynamic stability of two interacting Bose-Einstein condensates moving through each other with a relative velocity vr. We show that there exists a critical velocity vr(c) such that for vr>vr(c) the condensate mixture becomes unstable. We construct an analytic expression of the critical relative velocity and determine the unstable collective modes. We also discuss how our results can be applied to matter-wave-mixing processes.
The thermodynamic stability of a trapped Bose gas with a two-component condensate, e.g., a gas of atoms in two distinct hyperfine states or a binary gaseous mixture, is considered on the basis of modified Gross-Pitaevskii equations. Under certain conditions the system becomes unstable with respect to stratification, i.e., to spatial separation between the two condensates. One condensate assumes a donutlike spatial distribution, while the other retains a centered distribution. Possible applications of the theory to recent experimental data on two overlapping condensates in 87Rb are discussed.
We derive the dynamic and thermodynamic stability conditions for dilute multicomponent Bose-Einstein condensates (BECs). These stability conditions, generalized for n-component BECs, are found to be equivalent and are shown to be consistent with the phase diagrams of two- and three-component condensates that are derived from energetic arguments.
The development of modulation instability in a spatially homogeneous two-component Bose-Einstein condensate (BEC), in which the interacting components move through each other at a relative speed, is investigated. It is shown that nonlinear dynamics, leading to modulation instability, is determined by both the values of the constant interaction and the relative velocity between the components. The maximum oscillation increment is found and the limits of the existence of modulation instability in the space of wave numbers are determined.
The phase separation and vortex states in two-component Bose-Einstein condensate consisting of |F = 1,mf = −1> and |2,1> internal spin states of 87Rb atoms are considered in the framework of Thomas-Fermi approximation. It is shown that in nonrotating system the atoms in the state |1, −1> form a shell about the atoms in the state |2,1>. The critical angular velocity for each state is calculated. These velocities depend drastically on the relative concentrations of the components, the critical angular velocity of the outer component being less than the angular velocity of the inner one. It is shown that the atoms in the |1, −1> state can form a rotating ring about the resting core of the atoms in the state |2,1>. PACS:03.75.Fi; 05.30.Jp; 32.80.Pj. The realization of Bose-Einstein Condensation (BEC) in dilute atomic gases offers new opportunities for studying quantum degenerate fluids [1]. These condensates, which contain thousands of atoms confined to microscale clouds, have similarities to superfluidity and laser,
The question of the critical velocities of superfluid motion in a homogeneous, slightly nonideal two-component Bose gas with point interactions between particles is examined on the basis of the Landau criterion. It is shown that in the motion of the components with different velocities, the velocity of each component is not necessarily less than the minimal phase velocity of the elementary excitations in the nonmoving condensate. The Landau criterion leads to a joint condition on the values of the velocities of the components and the angle between them. It is found that the maximum value of the critical velocity of a given component can be achieved when the other component is at rest or when the components move in mutually perpendicular directions. The results are generalized to the case of a long-range interaction between particles and also for an inhomogeneous two-component Bose gas confined in a cylindrical harmonic potential. It is shown that in these cases the behavior of the critical velocities is qualitatively similar to that in a homogeneous two-component system with point interactions.