By performing high-resolution two-color photoassociation spectroscopy, we have successfully determined the binding energies of several of the last bound states of the homonuclear dimers of six different isotopes of ytterbium. These spectroscopic data are in excellent agreement with theoretical calculations based on a simple model potential, which very precisely predicts the
s-wave scattering lengths of all 28 pairs of the seven stable isotopes. The
s-wave scattering lengths for collision of two atoms of the same isotopic species are 13.33(18) nm for
168Yb, 3.38(11) nm for
170Yb, $\ensuremath{-}0.15(19)\text{ }\text{nm}$ for
171Yb, $\ensuremath{-}31.7(3.4)\text{ }\text{nm}$ for
172Yb, 10.55(11) nm for
173Yb, 5.55(8) nm for
174Yb, and $\ensuremath{-}1.28(23)\text{ }\text{nm}$ for
176Yb. The coefficient of the lead term of the long-range van der Waals potential of the
Yb2 molecule is
C6=1932(30) atomic units $({E}_{h}{a}_{0}^{6}\ensuremath{\approx}9.573\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{J}\text{ }{\text{nm}}^{6})$.
We report the use of photoassociative spectroscopy to determine the ground-state
s-wave scattering lengths for the main bosonic isotopes of strontium,
86Sr and
88Sr. Photoassociative transitions are driven with a laser red detuned by up to 1400 GHz from the $^{1}S_{0}\mathrm{\text{\ensuremath{-}}}^{1}P_{1}$ atomic resonance at 461 nm. A minimum in the transition amplitude for
86Sr at $\ensuremath{-}494\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{GHz}$ allows us to determine the scattering lengths
610a0<a86<2300a0 for
86Sr and a much smaller value of $\ensuremath{-}1{a}_{0}<{a}_{88}<13{a}_{0}$ for
88Sr.
In photoassociation spectroscopy, the line intensities of a given vibrational progression exhibit zero-signal modulation reflecting the node structure of the
s-wave ground state wave function of two free colliding atoms. This leads to the determination of the scattering length. We performed photoassociation of cold Cs atoms polarized in the Zeeman sublevel
f=4,
mf=4. We analyzed the intensities of the lines associated with the
Cs2 ${0}_{g}^{\ensuremath{-}}$ state dissociating to the
6s1/2+6p3/2 asymptote. This yields a value of the Cs triplet state scattering length, ${a}_{T}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}530a}_{0}$, while consistency requirements impose a value of the multipole ground state molecular coefficient,
C6=6510 a.u.
We have investigated the photoassociation (PA) spectra of ultracold
88Sr atoms near the $5s^2 ^1S_0+5s5p ^1P_1$ atomic asymptote. The intensity modulation of the PA lines was used to reconstruct the ground-state scattering wave function, whose nodal point inferred the s-wave scattering length of
a=1.1(2) nm. The observed PA resonances also determined a precise lifetime of the
1P1 state to be 5.263(4) ns.
The properties of bosonic ytterbium photoassociation spectra near the intercombination transition ${^{1}S}_{0}\ensuremath{-}{^{3}P}_{1}$ are studied theoretically at ultralow temperatures. We demonstrate how the shapes and intensities of rotational components of optical Feshbach resonances are affected by mass tuning of the scattering properties of the two colliding ground-state atoms. Particular attention is given to the relationship between the magnitude of the scattering length and the occurrence of shape resonances in higher partial waves of the van der Waals system. We develop a mass-scaled model of the excited-state potential that represents the experimental data for different isotopes. The shape of the rotational photoassociation spectrum for various bosonic Yb isotopes can be qualitatively different.
We model the binding energies of rovibrational levels of the RbYb molecule using experimental data from two-color photoassociation spectroscopy in mixtures of ultracold
87Rb with various Yb isotopes. The model uses a theoretical potential based on state-of-the-art ab initio potentials, further improved by least-squares fitting to the experimental data. We have fixed the number of bound states supported by the potential curve, so that the model is mass scaled, that is, it accurately describes the bound-state energies for all measured isotopic combinations. Such a model enables an accurate prediction of the
s-wave scattering lengths of all isotopic combinations of the RbYb system. The reduced mass range is broad enough to cover the full scattering lengths range from $\ensuremath{-}\ensuremath{\infty}$ to $+\ensuremath{\infty}$. For example, the
87Rb
174Yb system is characterized by a large positive scattering length of
+880(120) a.u., while
87Rb
173Yb has $a=\ensuremath{-}626(88)$ a.u. On the other hand
87Rb
170Yb has a very small scattering length of $\ensuremath{-}11.5(2.5)$ a.u. confirmed by the pair's extremely low thermalization rate. For isotopic combinations including
85Rb the variation of the interspecies scattering lengths is much smoother ranging from
+39.0(1.6) a.u. for
85Rb
176Yb to
+230(12) a.u. in the case of
85Rb
168Yb. Hyperfine corrections to these scattering lengths are also given. We further complement the fitted potential with interaction parameters calculated from alternative methods. The recommended value of the van der Waals coefficient is
C6=2837(13) a.u. agrees with but is more precise than the current state-of-the-art theoretical predictions [M. S. Safronova, S. G. Porsev, and C. W. Clark, Phys. Rev. Lett. 109, 230802 (2012)].