Mass scaling and non-adiabatic effects in photoassociation spectroscopy of ultracold strontium atoms

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 $^1S_0$$+$$^3P_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 $^1S_0$$+$$^3P_1$ $0_u^+$ ($^3\Pi_u$) and $^1S_0$$+$$^1D_2$ $0_u^+$ ($^1\Sigma^+_u$) potential 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.Comment: 14 pages, 7 tables, 5 figures. Submitted to Phys. Rev.

Absolute measurement of the ^{1}S_{0} − ^{3}P_{0} clock transition in neutral ^{88}Sr over the 330 km-long stabilized fibre optic link

We report a stability below $7\times 10{}^{-17}$ of two independent optical lattice clocks operating with bosonic ${}^{88}$Sr isotope. The value (429228066418008.3(1.9)${}_{syst}$(0.9)${}_{stat}$~Hz) of the absolute frequency of the ${}^{1}S_{0}$ - ${}^{3}P_{0}$ transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures

Accuracy budget of the 88Sr^{88}Sr optical atomic clocks at KL FAMO

This paper presents a detailed accuracy budget of two independent strontium optical lattice clocks at the National Laboratory FAMO (KL FAMO) probed with a single shared ultra-narrow laser. The combined instability of the two frequency standards was $7 \times 10^{-17}$ after $10^{5}s$ of averaging