title: Polaritonic solitons in a Bose-Einstein condensate trapped in a soft optical lattice.
abstract: We investigate the ground state (GS) of a collisionless Bose-Einstein condensate (BEC) trapped in a soft one-dimensional optical lattice (OL), which is formed by two counterpropagating optical beams perturbed by the BEC density profile through the local-field effect (LFE). We show that LFE gives rise to an envelope-deformation potential, a nonlocal potential resulting from the phase deformation, and an effective self-interaction of the condensate. As a result, stable photon-atomic (polaritonic) lattice solitons, including an optical component, in the form of the deformation of the soft OL, in a combination with a localized matter-wave component, are generated in the blue-detuned setting, without any direct interaction between atoms. These self-trapped modes, which realize the system's GS, are essentially different from the gap solitons supported by the interplay of the OL potential and collisional interactions between atoms. A transition to tightly bound modes from loosely bound ones occurs with the increase of the number of atoms in the BEC.
authors.affiliation: State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, 3663, North Zhongshan Road, Shanghai 200062, China. dong.guangjiong@gmail.com
authors.forename: Guangjiong
authors.initials: G
authors.lastname: Dong
authors.forename: Jiang
authors.initials: J
authors.lastname: Zhu
authors.forename: Weiping
authors.initials: W
authors.lastname: Zhang
authors.forename: Boris A
authors.initials: BA
authors.lastname: Malomed