Rabi Oscillations between Atomic and Molecular Condensates Driven with Coherent One-Color Photoassociation

Abstract

We demonstrate coherent one-color photoassociation of a Bose-Einstein condensate, which results in Rabi oscillations between atomic and molecular condensates. We attain atom-molecule Rabi frequencies that are comparable to decoherence rates by driving photoassociation of atoms in an 88 Sr condensate to a weakly bound level of the metastable 1 S0+ 3 P1 molecular potential, which has a long lifetime and a large Franck-Condon overlap integral with the ground scattering state. Transient shifts and broadenings of the excitation spectrum are clearly seen at short times, and they create an asymmetric excitation profile that only displays Rabi oscillations for blue detuning from resonance.Coherent conversion of atoms into molecules in quantum degenerate gases provides a path to create molecular condensates, and it is also of fundamental interest because of the complex dynamics of many-body systems with nonlinear couplings [1]. It has been demonstrated with magnetic-field ramps near a magnetic Feshbach resonance (MFR) [2,3] and with different configurations of two-color photoassociation (PA) [4][5][6][7]. Coherent onecolor PA has typically been considered inaccessible due to the short lifetime of excited molecular states in alkalimetal atoms [8]. In addition, the observation of giant Rabi oscillations between atomic and molecular condensates has remained elusive, although it has been discussed extensively since the earliest days of the study of quantum gases [8][9][10][11][12][13][14][15][16][17][18][19]. Here, we demonstrate coherent, one-color PA and Rabi oscillations between atomic and molecular condensates. We also observe transient shifts and broadenings of the excitation spectra at short times and indications of universal dynamics on resonance [8], all of which have not been experimentally studied previously. We access the coherent regime by photoassociating atoms in an 88 Sr condensate [20] to a weakly bound level of the metastable 1 S 0 + 3 P 1 molecular potential. This yields a long molecular lifetime and a large Franck-Condon overlap integral between ground and excited states, which allows atom-molecule coupling to exceed loss and decoherence rates. [6,28]. These two-color processes are typically coherent, as demonstrated, for example, by the suppression of PA loss [4]. Rabi oscillations between atomic and ground molecular condensates driven by twocolor PA [12,[14][15][16] have never been observed, even in optical lattices [5], although two-photon Raman coupling was recently used to observe Rabi oscillations in a degenerate Fermi gas [29]. Spontaneous Raman scattering by molecules presents a formidable challenge to accessing a regime in which the two-photon coupling exceeds the decoherence rate [5].Coherence seems even less accessible in one-color PA because of the short lifetime of excited molecular states. Simply increasing the laser intensity and atom-molecule Rabi frequency does not necessarily offer a solution because transfer of population to noncondensate atomic states becomes dominant at high laser cou...

Photoassociative cooling and trapping of a pair of interacting atoms

“…These experimental results and the recent observation of Rabi oscillations in PA [18,19] indicate that a two-level type treatment of a free-bound system is possible. Third, by standard Sisyphus method one can trap single atoms while by our proposed method one can trap the c.m.…”

“…In narrow-line PA systems, cyclic PA transitions or Rabi oscillations between an excited molecular bound state and the continuum of ground-state scattering states are possible as can be evidenced from experiments [18,19].…”

“…These recent advances towards laser cooling of diatomic molecules and coherent PA [18,19] motivate us to explore Sisyphus-like scheme to cool and trap an analogous system of a pair of atoms in a state of slow collision. This will allow one to optically control both the relative and c.m.…”

“…We show that it is indeed possible by coherent manipulation of the coupled motion of atom-pairs with counter-propagating PA lasers in lin ⊥ lin configuration. Coherent coupling in a PA system requires that the excited molecular states to which PA lasers are tuned should have life time long and a relatively large Franck-Condon (FC) overlap integral with the scattering state of ground-state atoms [18,19]. The recent experimental demonstrations of Rabi oscillations in two-electron atomic systems such as Sr [18] and Yb [19] making use of ultra narrow intercombination PA transitions strongly suggest that such PA systems can be treated in a way somewhat analogous to the methods used for two-level atoms.…”

Multiple transitions of coupled atom-molecule bosonic mixtures in two dimensions

“…A valid alternative (or complement) to Feshbach association of molecules is represented by photo-association, which has the advantage of creating deeply bound molecules (down to their rotovibrational ground state [46,47]), and which has recently been demonstrated to lead to coherent oscillations between atomic and molecular BECs [48]. In the following we will assume that the coherent atom-molecule coupling Γ in Eq.…”