Towards the production of ultracold ground-state RbCs molecules: Feshbach resonances, weakly bound states, and the coupled-channel model

Abstract

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We have studied interspecies scattering in an ultracold mixture of 87 Rb and 133 Cs atoms, both in their lowestenergy spin states. The three-body loss signatures of 30 incoming s-and p-wave magnetic Feshbach resonances over the range 0 to 667 G have been cataloged. Magnetic field modulation spectroscopy was used to observe molecular states bound by up to 2.5 MHz × h. We have created RbCs Feshbach molecules using two of the resonances. Magnetic moment spectroscopy along the magnetoassociation pathway from 197 to 182 G gives results consistent with the observed and calculated dependence of the binding energy on magnetic field strength. We have set up a coupled-channel model of the interaction and have used direct least-squares fitting to refine its parameters to fit the experimental results from the Feshbach molecules, in addition to the Feshbach resonance positions and the spectroscopic results for deeply bound levels. The final model gives a good description of all the experimental results and predicts a large resonance near 790 G, which may be useful for tuning the interspecies scattering properties. Quantum numbers and vibrational wave functions from the model can also be used to choose optimal initial states of Feshbach molecules for their transfer to the rovibronic ground state using stimulated Raman adiabatic passage.

Ground- and excited-state properties of the polar and paramagnetic RbSr molecule: A comparative study

“…In 2008 two groups have reported the formation of ultracold gases of polar LiCs and KRb molecules in ultracold temperatures [7,8]: ultracold LiCs molecules have been obtained by photoassociation of pairs of ultracold Li and Cs atoms and spontaneous decay of excited LiCs * molecule down to the electronic ground state, while ultracold KRb molecules have been created through magnetoassociation of ultracold K and Rb atoms into weakly bound levels of the molecular ground state, followed by stimulated Raman adiabatic passage (STIRAP) toward the lowest rovibrational level [9,10]. There is also a number of other experiments aiming at creating ultracold heteronuclear diatomic alkalimetal molecules in their ground state like RbCs [11,12] and NaK [13], since in contrast with KRb [14] they are stable with respect to the chemical reactions of atom exchange and trimer formation [15].…”

Feshbach spectroscopy of an ultracold mixture of85Rb and133Cs

“…An attractive alternative is to form ground-state RbCs, which is expected to be collisionally stable because both the exchange reaction 2RbCs → Rb 2 + Cs 2 and trimer formation reactions are endothermic [14]. There has been considerable work on the Feshbach resonances [15] and molecule formation [16,17] in 87 Rb 133 Cs. However, this isotopologue has an interspecies background scattering length that is large and positive, which produces a spatial separation of the dual condensate [18] and enhances losses from three-body collisions [19,20].…”

“…The interspecies scattering length and bound-state positions are calculated from a coupled-channel model, using the potential curves of Ref. [17], which were fitted to Fourier transform spectra of both 85 The scattering calculations are carried out using the MOLSCAT program [26], as modified to handle collisions in an external field [27]. The calculations use a fixed-step log-derivative propagator [28] to propagate from 0.3 to 1.9 nm and then the variable-step Airy propagator [29] to propagate from 1.9 to 1500 nm.…”

Driving the formation of the RbCs dimer by a laser pulse: A nonlinear-dynamics approach

“…In particular, starting from a gas of ultracold atoms, the photoassociation [7,8], the magneto-association [10] and the stimulated Raman adiabatic passage (STIRAP) [11], are among the usual techniques to create cold and ultracold molecules. These experimental techniques have been successfully applied to form different homonuclear and heteronuclear alkali diatomic molecules in the rovibrational ground state, such as C 2 [12,13], LiCs [14], KRb [15] or RbCs [16][17][18]. Furthermore, a number of theoretical studies have guided and promoted many of the experimental achievements.…”