Generation of bright atomic and molecular solitons in hybrid atom-molecular Bose-Einstein condensates coupled through raman photoassociation

Abstract

We have explored the feasibility of designing atomic and molecular bright solitons in a hybrid atom-molecular BEC (Bose Einstein Condensate) system of 87Rb coupled through Raman Photoassociation. It is found that the atomic and molecular waves when allowed to evolve in a spherical one-dimensional trap, initially oscillate with time and assume solitonic nature as bright solitons with progress in time. After the trap is switched off, atomic and molecular waves propagate retaining its solitonic nature and the final amplitude and nature of the bright solitons depend on the time of evolution within the trap. For this study we have used system parameters which are experimentally realizable. We have imposed random perturbation (5%) on the initial atomic and molecular wavefunctions, which are the solution of time independent coupled equation (without decay) and studied the evolution of atomic and molecular solitons with trap on and off condition. A small regular or large irregular oscillation in the amplitude of atomic solitons during evolution of perturbed matter waves are imposed depending on the system parameters. However broad molecular solitons with slowly decaying amplitude are generated which oscillate symmetrically around the centre of the trap. It is found that the stability and the shape of the generated atomic and molecular bright solitons can be controlled by varying the system parameters e.g. initial number of atoms, decay rates of the excited molecule and the frequency of the trap. Since the boson-boson interaction and the atom-molecular coupling strength depend on the total number of atoms, one can control the interplay between boson-boson interaction (due to s-wave scattering) and the atom-molecular coupling (through Raman Photoassociation) by varying the total number of atoms. It is found that with the increase in trap frequency generation of atomic and molecular solitons in atom-molecular coupled system is feasible if the strength of atom-molecular coupling and two-photon detuning is increased. The shape and the stability of the bright solitonic waves depend significantly on the strength of induced decay from the excited molecular state to the two-atom continuum or to the bound vibrational levels of the ground state. Stable flat-top atomic and molecular matter wave pulse can be generated from this atom-molecular coupled system by increasing the decay rates of the excited molecules.