We present high-resolution two-color photoassociation spectroscopy of Bose-Einstein condensates of ytterbium atoms. The use of narrow Raman resonances and careful examination of systematic shifts enabled us to measure 13 bound state energies for three isotopologues of the ground state ytterbium molecule with standard uncertainties on the order of 500 Hz. The atomic interactions are modeled using an ab initio based mass scaled Born-Oppenheimer potential whose long range van der Waals parameters and total WKB phase are fitted to experimental data. We find that the quality of the fit of this model, of about 112.9 kHz (RMS) can be significantly improved by adding the recently calculated beyond-Born-Oppenheimer (BBO) adiabatic corrections [

We model the binding energies of rovibrational levels of the RbYb molecule using experimental data from two-color photoassociation spectroscopy in mixtures of ultracold 87 Rb 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 −∞ to +∞. For example, the 87 Rb 174 Yb system is characterized by a large positive scattering length of +880 (120) Yb. 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 C 6 =2837(13) a.u. and is in agreement and more precise than the current state-of-the-art theoretical predictions (S. G. Porsev, M. S. Safronova, A. Derevianko, and C.W. Clark, arXiv:1307.2654).

We report photoassociation spectroscopy of ultracold 86 Sr atoms near the intercombination line and provide theoretical models to describe the obtained bound state energies. We show that using only the molecular states correlating with the 1 S 0 + 3 P 1 asymptote is insufficient to provide a mass scaled theoretical model that would reproduce the bound state energies for all isotopes investigated to date:84 Sr, 86 Sr and 88 Sr. We attribute that to the recently discovered avoided crossing between the 1 S 0potential curves at short range and we build a mass scaled interaction model that quantitatively reproduces the available 0 + u and 1 u bound state energies for the three stable bosonic isotopes. We also provide isotope-specific two-channel models that incorporate the rotational (Coriolis) mixing between the 0 + u and 1 u curves which, while not mass scaled, are capable of quantitatively describing the vibrational splittings observed in experiment. We find that the use of state-of-the-art ab initio potential curves significantly improves the quantitative description of the Coriolis mixing between the two −8 GHz bound states in 88 Sr over the previously used model potentials. We show that one of the recently reported energy levels in 84 Sr does not follow the long range bound state series and theorize on the possible causes. Finally, we give the Coriolis mixing angles and linear Zeeman coefficients for all of the photoassociation lines. The long range van der Waals coefficients C 6 (0 + u ) = 3868(50) a.u. and C 6 (1 u ) = 4085(50) a.u. are reported.

The properties of bosonic Ytterbium photoassociation spectra near the intercombination transition 1 S0-3 P1 are studied theoretically at ultra low 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 report the successful production of subradiant states of a two-atom system in a three-dimensional optical lattice starting from doubly occupied sites in a Mott insulator phase of a quantum gas of atomic ytterbium. We can selectively produce either a subradiant 1(g) state or a superradiant 0(u) state by choosing the excitation laser frequency. The inherent weak excitation rate for the subradiant 1(g) state is overcome by the increased atomic density due to the tight confinement in a three-dimensional optical lattice. Our experimental measurements of binding energies, linewidth, and Zeeman shift confirm the observation of subradiant levels of the 1(g) state of the Yb(2) molecule.

We present a comprehensive theoretical study of the electronic structures of the Yb atom and the Yb 2 molecule, respectively, focusing on their ground and lowest-lying electronically excited states. Our study includes various state-of-the-art quantum chemistry methods such as CCSD, CCSD(T), CASPT2 (including spin-orbit coupling), and EOM-CCSD as well as some recently developed pCCD-based approaches and their extensions to target excited states. Specifically, we scan the lowest-lying potential energy surfaces of the Yb 2 dimer and provide a reliable benchmark set of spectroscopic parameters including optimal bond lengths, vibrational frequencies, potential energy depths, and adiabatic excitation energies. Our in-depth analysis unravels the complex nature of the electronic spectrum of Yb 2 , which is difficult to model accurately by any conventional quantum chemistry method. Finally, we scrutinize the biexcited character of the first 1 Σ + g excited state and its evolution along the potential energy surface. K E Y W O R D S relativistic effects, electron corellation effects, spin-orbit coupling, equation of motion coupled cluster, CASPT2 | INTRODUCTIONThe divalent ytterbium atom has in recent years garnered significant attention thanks to its many uses in cold atom physics. It has a nonmagnetic 1 S 0 ground state and several useful optical transitions: the strong 1 S 0 $ 1 P 1 line can be used for Zeeman slowing, whereas the narrow (181 kHz) intercombination 1 S 0 $ 3 P 1 line can be used to directly laser cool Yb atoms to microkelvin temperatures. [1] Yb has seven stable isotopes: two fermions (171 and 173 with nuclear spins of 1/2 and 5/2, respectively) and five bosons (168, 170, 172, 174, and 176) that lack nuclear spin. The rich isotope structure makes it possible to mass-tune the atomic interactions [2] and facilitates a wide array of possible quantum-degenerate gases. [3][4][5][6] The doubly forbidden 1 S 0 $ 3 P 0 transition lies at the heart of optical atomic clocks [7] that are among the most precise physical instruments known to mankind. For example, an ytterbium clock has recently been demonstrated to enable geopotential measurements with an accuracy below a centimeter. [8] The long-lived 3 P 0 clock states also find use in quantum simulations using Yb atoms. [9] The long-range interactions in the Yb dimer have been probed extensively by high-resolution photoassociation spectroscopy (PAS) [10] near the narrow 1 S 0 $ 3 P 1 intercombination line. The excited 1 S 0 + 3 P 1 (0 + u ) [11,12] state has been probed by single color PAS and provided the van der Waals C 6 coefficient and an improved value of the atomic 3 P 1 lifetime. Two-color PAS of ground state 0 + g vibrational levels [2,13] delivered accurate

Optical molecular clocks promise unparalleled sensitivity to the temporal variation of the electron-to-proton mass ratio and insight into possible new physics beyond the standard model. We propose to realize a molecular clock with bosonic ^{174}Yb_{2} molecules, where the forbidden ^{1}S_{0}→^{3}P_{0} clock transition would be induced magnetically. The use of a bosonic species avoids possible complications due to the hyperfine structure present in fermionic species. While direct clock line photoassociation would be challenging, weakly bound ground state molecules could be produced by stimulated Raman adiabatic passage and used instead. The recent scattering measurements [L. Franchi, et al. New J. Phys. 19, 103037 (2017)NJOPFM1367-263010.1088/1367-2630/aa8fb4] enable us to determine the positions of target ^{1}S_{0}+^{3}P_{0} vibrational levels and calculate the Franck-Condon factors for clock transitions between ground and excited molecular states. The resulting magnetically induced Rabi frequencies are similar to those for atoms hinting that an experimental realization is feasible. A successful observation could pave the way towards Hz-level molecular spectroscopy.

Several extensions to the Standard Model of particle physics, including light dark matter candidates and unification theories predict deviations from Newton’s law of gravitation. For macroscopic distances, the inverse-square law of gravitation is well confirmed by astrophysical observations and laboratory experiments. At micrometer and shorter length scales, however, even the state-of-the-art constraints on deviations from gravitational interaction, whether provided by neutron scattering or precise measurements of forces between macroscopic bodies, are currently many orders of magnitude larger than gravity itself. Here we show that precision spectroscopy of weakly bound molecules can be used to constrain non-Newtonian interactions between atoms. A proof-of-principle demonstration using recent data from photoassociation spectroscopy of weakly bound Yb2 molecules yields constraints on these new interactions that are already close to state-of-the-art neutron scattering experiments. At the same time, with the development of the recently proposed optical molecular clocks, the neutron scattering constraints could be surpassed by at least two orders of magnitude.