We report on the anomalously high line strength of a single rotational level in the ultracold photoassociation of two
85Rb atoms to form
85Rb
2. The ${v}^{\ensuremath{'}}=111$, ${J}^{\ensuremath{'}}=5$ level belongs to the Hund's case (c)
2(0g+) state, which correlates to the Hund's case (a) $2{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Sigma}}_{g}^{+}$ state. Its strength is caused by coupling with a very near-resonant long-range state. The long-range component is the energetically degenerate ${v}^{\ensuremath{'}}=155$, ${J}^{\ensuremath{'}}=5$ level of the case (c)
2(1g) state, correlating to the case (a) $1{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Pi}}_{g}$ state. The line strength is enhanced by an order of magnitude through this coupling, relative to nearby vibrational levels and even to nearby rotational levels of the same vibrational level. This enhancement is in addition to the enhancement seen in all ${J}^{\ensuremath{'}}=3$ and 5 levels of the
2(0g+) state due to an
l=4 shape resonance in the $a{\phantom{\rule{0.16em}{0ex}}}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state continuum, which alters the distribution of levels formed by photoassociation.
We have successfully prepared an optically trapped ultracold mixture of
23Na and
87Rb atoms and studied their interspecies Feshbach resonances. Using two different spin combinations, several
s- and
p-wave resonances are identified by observing high inelastic losses and temperature increases for both species near resonant magnetic field values. The two
s-wave resonances observed below 500 G between atoms in their lowest-energy levels are possible candidates for Feshbach molecule association. Our results are well characterized by a coupled-channel model which also refines the ground-state interaction potentials between
23Na and
87Rb. This work opens up the prospect for preparing ultracold ensembles of ground-state bosonic NaRb molecules which are chemically stable and can provide strong dipolar interactions.
State-Selective Detection of Ultracold High-
v Ground-State Rb
2, and Spectroscopy of the (2)
1Σu+ State
We investigate magnetic Feshbach resonances in two different ultracold K-Rb mixtures. Information on the $^{39}\text{K}\text{\ensuremath{-}}^{87}\text{R}\text{b}$ isotopic pair is combined with preexisting observations of resonance patterns for $^{40}\text{K}\text{\ensuremath{-}}^{87}\text{R}\text{b}$. Interisotope resonance spectroscopy improves significantly our near-threshold model for scattering and bound-state calculations. Our analysis determines the number of bound states in singlet and triplet potentials and establishes precisely near-threshold parameters for all K-Rb pairs of interest for experiments with both atoms and molecules. In addition, the model verifies the validity of the Born-Oppenheimer approximation at the present level of accuracy.