Precise measurements of the masses of Cs, Rb and Na - A new route to the fine structure constant

We report new values for the atomic masses of the alkali (CS)-C-133, Rb-87, Rb-85, and Na-13 with uncertainties less than or equal to0.2 ppb. These re sults, obtained using Penning trap single ion mass spectrometry, are typica lly two orders of magnitude more accurate than previously measured values. Combined with values of h/m atom from atom interferometry measurements and accurate wavelength measurements for different atoms, these values will lea d to new ppb-level determinations of the molar Planck constant N(A)h and th e fine structure constant alpha. This route to alpha is based on simple phy sics. It can potentially achieve the several ppb level of accuracy needed t o test the QED determination of alpha extracted from measurements of the el ectron g factor. We also demonstrate an electronic cooling technique that c ools our detector and ion below the 4 K ambient temperature. This technique improves by about a factor of three our ability to measure the ion's axial motion.