Beyond-mean-field effects in Rabi-coupled two-component Bose-Einstein condensate

L Lavoine (1) , A Hammond (1) , A Recati (2) , D S Petrov (3) , T Bourdel (1)

1 Laboratoire Charles Fabry / Gaz Quantiques
2 UNITN - Università degli Studi di Trento = University of Trento
3 LPTMS - Laboratoire de Physique Théorique et Modèles Statistiques

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 $\Omega$, the BMF energy density crosses over from the nonanalytic Lee-Huang-Yang (LHY) scaling $\propto n^{5/2}$ to an expansion in integer powers of density, where, in addition to a two-body BMF term $\propto n^2 \sqrt{\Omega}$, there emerges a repulsive three-body contribution $\propto n^3/\sqrt{\Omega}$. We experimentally evidence these two contributions, thanks to their different scaling with $\Omega$, in the expansion of a Rabi-coupled two-component $^{39}$K 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.

Domaines: Gaz Quantiques [cond-mat.quant-gas]; Physique Quantique [quant-ph]

L Lavoine, A Hammond, A Recati, D S Petrov, T Bourdel. Beyond-mean-field effects in Rabi-coupled two-component Bose-Einstein condensate. Physical Review Letters, 2021, ⟨10.1103/PhysRevLett.127.203402⟩. ⟨hal-03232484v4⟩