Feshbach-Resonance-Enhanced Coherent Atom-Molecule Conversion with Ultranarrow Photoassociation Resonance

Abstract

We reveal the existence of high-density Feshbach resonances in the collision between the ground and metastable states of 171 Yb and coherently produce the associated Feshbach molecules by photoassociation. The extremely small transition rate is overcome by the enhanced Franck-Condon factor of the weakly bound Feshbach molecule, allowing us to observe Rabi oscillations with long decay time between an atom pair and a molecule in an optical lattice. We also perform the precision measurement of the binding energies, which characterizes the observed resonances. The ultra-narrow photoassociation will be a basis for practical implementation of optical Feshbach resonances. [2][3][4], the initial step to form an ultracold, ro-vibronic ground state of (polar) molecules [5,6], correlation measurements for ultracold atoms in an optical lattice [7][8][9], and so on. Photoassociation (PA) is another standard method to generate ultracold molecules which can create various molecules in electronic excited states with a simple optical excitation. [10]. However, the transition probability is never large enough even for a strong electric-dipole allowed (E1) transition due to small overlap between the wave functions of free atoms and molecular bound states, resulting in small FranckCondon factors. In addition, the radiative lifetime of the created molecular states is usually quite short for an E1 transition. As a consequence, coherent production of molecules by one-color PA has been impossible until recent demonstration with a BEC of 88 Sr [11], where the narrow 1 S 0 ↔ 3 P 1 transition was exploited.In this Letter, we report on photoassociative creation of ultracold molecules associated with the ground 1 S 0 and long-lived metastable 3 P 2 states of 171 Yb with a radiative lifetime of longer than one second. Importantly, the otherwise quite small strength of the PA resonance is significantly enhanced by working around FRs for the closed channel. This enables us to demonstrate Rabi oscillations in the PA transition with a lifetime reaching hundreds of microseconds. Moreover, by using this narrow-line PA, observed FRs are characterized by precise measurement of the binding energies of near-threshold Fesbach molecules. Our observation of the strong PA line with a long expected radiative lifetime opens up the possibility to suppress atom loss in optical Feshbach resonances [11][12][13].First, we describe our observation of FRs in collisions between 1 S 0 and 3 P 2 states of 171 Yb, which is an important basis in this work. Most of the currently studied FRs are for alkali atoms, which originate from their hyperfine structures with isotropic van der Waals interactions. On the other hand, the emergence of FRs associated with the existence of anisotropic interactions was recently predicted [14] and observed in collisions of Er [15] and Dy [16]. For these atoms, anisotropy in an electrostatic van der Waals potentials with non-zero electronic orbital angular momenta as well as dipole-dipole interactions induces couplings between an open cha...

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].…”

“…The interatomic separations at which PA transitions take place are typically far below or of the order of a nanometer. So, unless trapping size is reduced to a nanometer or less, PA process will not be affected by the trapping potential [19]. So, to subject a pair of cold atoms into counter-propagating PA lasers, one can prepare pairs of atoms in a two-atom Mott insulator where each lattice site is occupied by two atoms as is done in the recent experiment by Taie et.…”

“…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.…”

Manipulating nanoscale atom–atom interactions with cavity QED

“…We consider those kind of atoms which have either very long life time (typically in microsecond regime) or metastable excited states such as alkaline-earth metal atoms or other two valance electron systems such as ytterbium. In recent times, cold collision in meta-stable excited states has become important [35].…”