Transition to miscibility in linearly coupled binary dipolar Bose-Einstein condensates

TL;DR

This study explores how dipole-dipole interactions influence the transition between immiscible and miscible states in linearly coupled binary dipolar Bose-Einstein condensates, revealing conditions under which these transitions occur or are suppressed.

Contribution

It demonstrates that dipole-dipole interactions can induce or prevent miscibility transitions depending on dipole orientation and coupling, providing new insights into controlling BEC phase states.

Findings

IMT cannot be induced by DD interactions alone with same orientation dipoles.

Oppositely polarized dipoles can induce IMT without linear coupling.

Unstable localized states evolve into stable breathers, except under strong DD attraction.

Abstract

We investigate effects of dipole-dipole (DD) interactions on immiscibility-miscibility transitions (IMTs) in two-component Bose-Einstein condensates (BECs) trapped in the harmonic-oscillator (HO) potential, with the components linearly coupled by a resonant electromagnetic field (accordingly, the components represent two different spin states of the same atom). The problem is studied by means of direct numerical simulations. Different mutual orientations of the dipolar moments in the two components are considered. It is shown that, in the binary BEC formed by dipoles with the same orientation and equal magnitudes, the IMT cannot be induced by the DD interaction alone, being possible only in the presence of the linear coupling between the components, while the miscibility threshold is affected by the DD interactions. However, in the binary condensate with the two dipolar components polarized in opposite directions, the IMT can be induced \emph{without} any linear coupling. Further, we demonstrate that those miscible and immiscible localized states, formed in the presence of the DD interactions, which are unstable evolve into robust breathers, which tend to keep the original miscibility or immiscibility, respectively. An exception is the case of a very strong DD attraction, when narrow stationary modes are destroyed by the instability. The binary BEC composed of co-polarized dipoles with different magnitudes are briefly considered too.