Prospects for application of ultracold Sr2_2 molecules in precision measurements

Precision measurements with ultracold molecules require development of robust and sensitive techniques to produce and interrogate the molecules. With this goal, we theoretically analyze factors that affect frequency measurements between rovibrational levels of the Sr$_2$ molecule in the electronic ground state. This measurement can be used to constrain the possible time variation of the proton-electron mass ratio. Sr$_2$ is expected to be a strong candidate for achieving high precision due to the spinless nature and ease of cooling and perturbation-free trapping of Sr \cite{Zelevinsky2008}. The analysis includes calculations of two-photon transition dipole moments between deeply and weakly bound vibrational levels, lifetimes of intermediate excited states, and Stark shifts of the vibrational levels by the optical lattice field, including possibilities of Stark-cancellation trapping.Comment: 8 pages, 10 figure

Precision Test of Mass Ratio Variations with Lattice-Confined Ultracold Molecules

We propose a precision measurement of time variations of the proton-electron mass ratio using ultracold molecules in an optical lattice. Vibrational energy intervals are sensitive to changes of the mass ratio. In contrast to measurements that use hyperfine-interval-based atomic clocks, the scheme discussed here is model-independent and does not require separation of time variations of different physical constants. The possibility of applying the zero-differential-Stark-shift optical lattice technique is explored to measure vibrational transitions at high accuracy.Comment: 4 pages, 4 figure

Dispersion interactions and reactive collisions of ultracold polar molecules

Progress in ultracold experiments with polar molecules requires a clear understanding of their interactions and reactivity at ultra-low collisional energies. Two important theoretical steps in this process are the characterization of interaction potentials between molecules and the modeling of reactive scattering mechanism. Here, we report on the {\it abinitio} calculation of isotropic and anisotropic van der Waals interaction potentials for polar KRb and RbCs colliding with each other or with ultracold atoms. Based on these potentials and two short-range scattering parameters we then develop a single-channel scattering model with flexible boundary conditions. Our calculations show that at low temperatures (and in absence of an external electric field) the reaction rates between molecules or molecules with atoms have a resonant character as a function of the short-range parameters. We also find that both the isotropic and anisotropic van der Waals coefficients have significant contributions from dipole coupling to excited electronic states. Their values can differ dramatically from those solely obtained from the permanent dipole moment. A comparison with recently obtained reaction rates of fermionic $^{40}$K$^{87}$Rb shows that the experimental data can not be explained by a model where the short-range scattering parameters are independent of the relative orbital angular momentum or partial wave.Comment: 15 pages, 12 figure

Optical Production of Stable Ultracold 88^{88}Sr2_2 Molecules

We have produced large samples of ultracold $^{88}$Sr$_2$ molecules in the electronic ground state in an optical lattice. The molecules are bound by 0.05 cm$^{-1}$ and are stable for several milliseconds. The fast, all-optical method of molecule creation via intercombination line photoassociation relies on a near-unity Franck-Condon factor. The detection uses a weakly bound vibrational level corresponding to a very large dimer. This is the first of two steps needed to create Sr$_2$ in the absolute ground quantum state. Lattice-trapped Sr$_2$ is of interest to frequency metrology and ultracold chemistry.Comment: 5 pages, 3 figure

Photoassociation spectroscopy of cold alkaline earth atoms near the intercombination line

The properties of photoassociation (PA) spectra near the intercombination line (the weak transition between $^{1}S_{0}$ and $^{3}P_{1}$ states) of group II atoms are theoretically investigated. As an example we have carried out a calculation for Calcium atoms colliding at ultra low temperatures of 1 mK, 1 $\mu$K, and 1 nK. Unlike in most current photoassociation spectroscopy the Doppler effect can significantly affect the shape of the investigated lines. Spectra are obtained using Ca--Ca and Ca--Ca$^*$ short-range {\it ab initio} potentials and long-range van der Waals and resonance dipole potentials. The similar van der Waals coefficients of ground $^{1}S_{0} + ^{1}S_{0}$ and excited $^{1}S_{0} + ^{3}P_{1}$ states cause the PA to differ greatly from those of strong, allowed transitions with resonant dipole interactions. The density of spectral lines is lower, the Condon points are at relatively short range, and the reflection approximation for the Franck-Condon factors is not applicable, and the spontaneous decay to bound ground-state molecules is efficient. Finally, the possibility of efficient production of cold molecules is discussed

Magic conditions for multiple rotational states of bialkali molecules in optical lattices

We investigate magic-wavelength trapping of ultracold bialkali molecules in the vicinity of weak optical transitions from the vibrational ground state of the X 1 Σ + potential to low-lying rovibrational states of the b 3 Π 0 potential, focusing our discussion on the 87 Rb 133 Cs molecule in a magnetic field of B = 181 G. We show that a frequency window exists between two nearest-neighbor vibrational poles in the dynamic polarizability where the trapping potential is “near magic” for multiple rotational states simultaneously. We show that the addition of a modest DC electric field of E = 0.13 kV/cm leads to an exact magic-wavelength trap for the lowest three rotational states at a angular-frequency detuning of Δ v ′ = 0 = 2 π × 218.22 GHz from the X 1 Σ + ( v = 0 , J = 0 ) → b 3 Π 0 ( v ′ = 0 , J = 1 ) transition. We derive a set of analytical criteria that must be fulfilled to ensure the existence of such magic frequency windows and present an analytic expression for the position of the frequency window in terms of a set of experimentally measurable parameters. These results should inform future experiments requiring long coherence times on multiple rotational transitions in ultracold polar molecules

Inelastic collisions of ultra-cold heteronuclear molecules in an optical trap

Ultra-cold RbCs molecules in high-lying vibrational levels of the a$^3\Sigma^+$ ground electronic state are confined in an optical trap. Inelastic collision rates of these molecules with both Rb and Cs atoms are determined for individual vibrational levels, across an order of magnitude of binding energies. A simple model for the collision process is shown to accurately reproduce the observed scattering rates

Collisional stability of localized Yb(3P2{}^3\mathrm{P}_2) atoms immersed in a Fermi sea of Li

We establish an experimental method for a detailed investigation of inelastic collisional properties between ytterbium (Yb) in the metastable ${}^3\mathrm{P}_2$ state and ground state lithium (Li). By combining an optical lattice and a direct excitation to the ${}^3\mathrm{P}_2$ state we achieve high selectivity on the collisional partners. Using this method we determine inelastic loss coefficients in collisions between $^{174}$Yb(${}^3\mathrm{P}_2$) with magnetic sublevels of $m_J=0$ and $-2$ and ground state $^6$Li to be $(4.4\pm0.3)\times10^{-11}~\mathrm{cm}^3/\mathrm{s}$ and $(4.7\pm0.8)\times10^{-11}~\mathrm{cm}^3/\mathrm{s}$, respectively. Absence of spin changing processes in Yb(${}^3\mathrm{P}_2$)-Li inelastic collisions at low magnetic fields is confirmed by inelastic loss measurements on the $m_J=0$ state. We also demonstrate that our method allows us to look into loss processes in few-body systems separately.Comment: 12 pages, 7 figure