[en] We have developed an atom trap trace analysis (ATTA) system to measure Kr in Xe at the part per trillion (ppt) level, a prerequisite for the sensitivity achievable with liquid xenon dark matter detectors beyond the current generation. Since Ar and Kr have similar laser cooling wavelengths, the apparatus has been tested with Ar to avoid contamination prior to measuring Xe samples. A radio-frequency plasma discharge generates a beam of metastable atoms which is optically collimated, slowed, and trapped using standard magneto-optical techniques. Based on the measured overall system efficiency of 1.2 × 10⁻⁸ (detection mode), we expect the ATTA system to reach the design goal sensitivity to ppt concentrations of Kr in Xe in <2 h

[en] With microkelvin neutral strontium atoms confined in an optical lattice, we have achieved a fractional resolution of better than 5x10^-15 on the ¹S₀-³P₀ doubly forbidden ⁸⁷Sr clock transition at 698 nm. Measurements of the clock line shifts as a function of experimental parameters indicate that the fractional uncertainties due to systematic shifts could be reduced below 10^-15. The ultrahigh spectral resolution permitted resolving the nuclear spin states of the clock transition at small magnetic fields, leading to measurements of the ³P₀ magnetic moment and metastable lifetime. In addition, photoassociation spectroscopy was performed on the narrow ¹S₀-³P₁ transition of ⁸⁸Sr, revealing the least-bound state, and showing promise for efficient optical tuning of the ground state scattering length and production of cold molecules.

[en] 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

[en] The study of ultracold molecules tightly trapped in an optical lattice can expand the frontier of precision measurement and spectroscopy, and provide a deeper insight into molecular and fundamental physics. Here we create, probe, and image microkelvin "8"8Sr_2 molecules in a lattice, and demonstrate precise measurements of molecular parameters as well as coherent control of molecular quantum states using optical fields. We discuss the sensitivity of the system to dimensional effects, a new bound-to-continuum spectroscopy technique for highly accurate binding energy measurements, and prospects for new physics with this rich experimental system. (paper)

[en] The absolute frequency of the ¹S0-³P0 clock transition of ⁸⁷Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6 * 10^-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a detailed study of systematic effects, which reduced the total systematic uncertainty of the Sr lattice clock to 1.5 * 10^-16, the clock frequency is measured against a hydrogen maser which is simultaneously calibrated to the US primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fibre transfer scheme to compare the remotely located clock signals. (authors)

[en] The ¹S₀-³P₀ clock transition frequency ν_Sr in neutral ⁸⁷Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1x10^-15 level makes ν_Sr the best agreed-upon optical atomic frequency. We combine periodic variations in the ⁸⁷Sr clock frequency with ¹⁹⁹Hg⁺ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant α, electron-proton mass ratio μ, and light quark mass. Furthermore, after ¹⁹⁹Hg⁺, ¹⁷¹Yb⁺, and H, we add ⁸⁷Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of α and μ

[en] With ultracold ⁸⁸Sr in a 1D magic wavelength optical lattice, we performed narrow-line photoassociation spectroscopy near the ¹S₀-³P₁ intercombination transition. Nine least-bound vibrational molecular levels associated with the long-range 0_u and 1_u potential energy surfaces were measured and identified. A simple theoretical model accurately describes the level positions and treats the effects of the lattice confinement on the line shapes. The measured resonance strengths show that optical tuning of the ground state scattering length should be possible without significant atom loss