Precision measurement based on ultracold atoms and cold molecules

Ultracold atoms and molecules provide ideal stages for precision tests of fundamental physics. With microkelvin neutral strontium atoms confined in an optical lattice, we have achieved a fractional resolution of 4 x 10-(15) on the S-1(0)-P-3(0) doubly-forbidden Sr-87 clock transition at 698 mn. The overall systematic uncertainty of the clock is evaluated below the 10(-15) level. The ultrahigh spectral resolution permits resolving the nuclear spin states of the clock transition at small magnetic fields, leading to measurements of the P-3(0) magnetic moment and metastable lifetime. In addition, photoassociation spectroscopy performed on the narrow S-1(0) - P-3(1) transition of Sr-88 shows promise for efficient optical tuning of the ground state scattering length and production of ultracold ground-state molecules. Lattice-confined Sr-2 molecules are suitable for constraining the time-variation of electron-proton mass ratio. In a separate experiment, cold, ground state polar molecules produced from Stark decelerators have enabled an order of magnitude improvement in measurement precision of ground-state, A-doublet microwave transitions in the OH molecule. Comparing the laboratory results to those from OH megamasers in interstellar space will allow a sensitivity of 10(-6) for measuring the potential time variation of the fundamental fine structure constant Delta alpha/alpha over 10(10) years. These results have also led to improved understandings in the molecular structure. The study of the low magnetic field behavior of OH in its (2)Pi(3/2) ro-vibronic ground state precisely determines a differential Lande g-factor between opposite parity components of the A-doublet.