We observe long-range 85 Rb and 87 Rb (24D+5S 1/2 ) Rydberg molecules for eight different spin couplings, with binding energies up to 440 MHz and sub-percent relative uncertainty. Isotopic effects of the molecular binding energies arise from the different masses and nuclear spins. Because the vibrational states involve different spin configurations and cover a wide range of internuclear separations, the states have different dependencies on the s-wave and p-wave scattering phase shifts for singlet and triplet scattering. This enables a comprehensive determination of all four scattering lengths from the spectroscopic data. Our unusually high temperature and low density (180 µK, 1 × 10 11 cm −3 ) suggest that the molecule excitation occurs through photo-assisted collisions.

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We develop a formalism for photoionization (PI) and potential energy curves (PECs) of Rydberg atoms in ponderomotive optical lattices and apply it to examples covering several regimes of the optical-lattice depth. The effect of lattice-induced PI on Rydberg-atom lifetime ranges from noticeable to highly dominant when compared with natural decay. The PI behavior is governed by the generally rapid decrease of the PI cross sections as a function of angular-momentum (ℓ), lattice-induced ℓ-mixing across the optical-lattice PECs, and interference of PI transition amplitudes from the lattice-mixed into free-electron states. In GHz-deep lattices, ℓ-mixing leads to a rich PEC structure, and the significant low-ℓ PI cross sections are distributed over many lattice-mixed Rydberg states. In lattices less than several tens-of-MHz deep, atoms on low-ℓ PECs are essentially ℓ-mixing-free and maintain large PI rates, while atoms on high-ℓ PECs trend towards being PI-free. Characterization of PI in GHz-deep Rydberg-atom lattices may be beneficial for optical control and quantum-state manipulation of Rydberg atoms, while data on PI in shallower lattices are potentially useful in high-precision spectroscopy and quantum-computing applications of lattice-confined Rydberg atoms.

Collisions with background atoms are known to induce a significant shift in the frequency of stateof-the-art optical atomic clocks and contribute to state decoherence in cold atom experiments. The effects of these collisions can be quantified by measuring their cross sections. We experimentally measured the collision cross section between 88 Sr−N2 in a Magneto-Optical Trap (MOT). The measurement was carried out by monitoring the atom number loss rate as a function of background pressure of N2 and the cross section thus obtained was 8.1(4)×10 −18 m 2 . The measured collision cross section has been utilized for the determination of C6 coefficient of the ground state ( 1 S0) of 88 Sr atom, which can be useful to estimate the relative frequency shift in the clock transition. We also estimate the loss rate induced by the combined effect of the decay of atoms in the long-lived 3 P 0 state and temperature-induced atomic losses from the capture volume of the MOT. We find that the contribution due to the latter is dominant in comparison to the other atomic loss channels and must be included in the studies that rely on the total loss rate measurement.

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