Beyond mean-field effects in two-components BEC

In mean-field theory, the ground state of a two-component Bose-Einstein condensate (BEC) in a uniform system is either uniformly mixed or totally separated. Beyond-mean-field effects introduce an additional phase, the mixed-bubble state, in which the two components remain mixed within one of the separated domains. Here we show that a mixed-bubble state can emerge in a binary mixture of spin-1 ${}^{7}{\rm{Li}}$ and ${}^{23}{\rm{Na}}$ BECs even within the mean-field framework. We further demonstrate the existence of a metastable uniformly-mixed state, which undergoes a transition to the mixed-bubble state triggered by a local perturbation.In mean-field theory, the ground state of a two-component Bose-Einstein condensate (BEC) in a uniform system is either uniformly mixed or totally separated. Beyond-mean-field effects introduce an additional phase, the mixed-bubble state, in which the two components remain mixed within one of the separated domains. Here we show that a mixed-bubble state can emerge in a binary mixture of spin-1 ${}^{7}{\rm{Li}}$ and ${}^{23}{\rm{Na}}$ BECs even within the mean-field framework. We further demonstrate the existence of a metastable uniformly-mixed state, which undergoes a transition to the mixed-bubble state triggered by a local perturbation.

arXiv:2609.39231Sep 30, 20260 citations

Beyond-Mean-Field Effects in Rabi-Coupled Two-Component Bose-Einstein Condensate

L. Lavoine, Hammond A., Recati A. +2 more

We theoretically calculate and experimentally measure the beyond-mean-field (BMF) equation of state in a coherently coupled two-component Bose-Einstein condensate (BEC) in the regime where averaging of the interspecies and intraspecies coupling constants over the hyperfine composition of the single-particle dressed state predicts the exact cancellation of the two-body interaction. We show that with increasing the Rabi-coupling frequency ?, the BMF energy density crosses over from the nonanalytic Lee-Huang-Yang scaling ?n5/2 to an expansion in integer powers of density, where, in addition to a two-body BMF term ?n2?, there emerges a repulsive three-body contribution ?n3/?. We experimentally evidence these two contributions, thanks to their different scaling with ?, in the expansion of a Rabi-coupled two-component K39 condensate in a waveguide. By studying the expansion with and without Rabi coupling, we reveal an important feature relevant for observing BMF effects and associated phenomena in mixtures with spin-asymmetric losses: Rabi coupling helps preserve the spin composition and thus prevents the system from drifting away from the point of the vanishing mean field.We theoretically calculate and experimentally measure the beyond-mean-field (BMF) equation of state in a coherently coupled two-component Bose-Einstein condensate (BEC) in the regime where averaging of the interspecies and intraspecies coupling constants over the hyperfine composition of the single-particle dressed state predicts the exact cancellation of the two-body interaction. We show that with increasing the Rabi-coupling frequency ?, the BMF energy density crosses over from the nonanalytic Lee-Huang-Yang scaling ?n5/2 to an expansion in integer powers of density, where, in addition to a two-body BMF term ?n2?, there emerges a repulsive three-body contribution ?n3/?. We experimentally evidence these two contributions, thanks to their different scaling with ?, in the expansion of a Rabi-coupled two-component K39 condensate in a waveguide. By studying the expansion with and without Rabi coupling, we reveal an important feature relevant for observing BMF effects and associated phenomena in mixtures with spin-asymmetric losses: Rabi coupling helps preserve the spin composition and thus prevents the system from drifting away from the point of the vanishing mean field.

Jan 1, 202136 citations

Analytic Beyond-Mean-Field BEC Wave Functions

Martin Dunn, W. Blake Laing, D. K. Watson +1 more

Bulletin of the American Physical SocietyMay 17, 20060 citations

{}^{7}{\rm{Li}}

and

{}^{23}{\rm{Na}}

BECs even within the mean-field framework. We further demonstrate the existence of a metastable uniformly-mixed state, which undergoes a transition to the mixed-bubble state triggered by a local perturbation.