Superchemistry: Dynamics of Coupled Atomic and Molecular Bose-Einstein Condensates

Abstract

We analyze the dynamics of a dilute, trapped Bose-condensed atomic gas coupled to a diatomic molecular Bose gas by coherent Raman transitions. This system is shown to result in a new type of "superchemistry," in which giant collective oscillations between the atomic and the molecular gas can occur. The phenomenon is caused by stimulated emission of bosonic atoms or molecules into their condensate phases.

Fock-state dynamics in Raman photoassociation of Bose-Einstein condensates

“…We note that scattering lengths can be tuned using Feshbach resonance techniques. The coupling parameter depends on both laser intensities and the one-photon detuning from the excited molecular levels, as well as on the overlap integrals of the states involved in the transition [1]. Using the same procedure as Kheruntsyan and Drummond [30], we find that the value of used here is comparable to the one used in that work, the value of the coupling equating to approximately 2.1 ϫ 10 −7 m 1/2 s −1 .…”

“…The first issue is superchemistry, or Raman photoassociation of condensed atoms to form a molecular condensate [1]. The second issue is the question of the actual quantum state of a trapped condensate, as described by the Wigner function, and whether knowledge of this state may be important for theoretical analyses.…”

“…Javanainen and Mackie [6] later proposed a twomode, phenomenological Hamiltonian to model the process of photoassociation. A more complete proposal, using an atomic and two molecular fields, coupled via a two-color Raman transition so as to minimize spontaneous-emission losses, was developed by Heinzen et al [1]. This model, which utilized the Gross-Pitaevskii equation (GPE) approach, demonstrated that the molecular formation would not obey the usual Arrhenius rules for chemical reactions and introduced the name superchemistry.…”

“…We consider a Raman photoassociation scheme [1,7,8] with the excited molecular field adiabatically eliminated. Following the same procedure as detailed in Ref.…”

“…Because of Pauli blocking of the dissociation channel, the dynamics of this process, even if it were to be carried out using photoassociative techniques, are expected to be different from those of superchemistry [17]. Photoassociation experiments have been performed using Raman techniques by Heinzen et al [18] and Gerton et al [19], although the atom-molecule oscillations predicted theoretically [1] were not observed. Molecules have also been formed from a sodium condensate by a single photon transition, although this method does have problems with their subsequent spontaneous breakup [20].…”