Precision α Measurement: Atom Recoil Method Review Victor Acosta Physics 250: Atomic Physics Prof. Dima Budker

Motivation α shows up all over in EM calcs α shows up all over in EM calcs Methods using g-2 involve lengthy QED equations which undergo frequent revision Working Toward an Electronic Kilogram…

Electronic Kg Balance Gravity Force with EMF Find value for h, Planck’s Constant Deduce m e from:

Physical Constant Uncertainties:

Determining α Measuring R∞: Compare transition frequencies in Hydrogen using frequency chain or comb. de Beauvoir et. al. Eur Phys J D 2000, Udem et. al Measuring m p /m e and M Atom /mp

Penning Trap Hans Dehmelt, Nobel Prize 1989 Hans Dehmelt, Nobel Prize 1989 Sub ppb UC for most mass ratios

Atom Recoil ~10 kHz So for ppb UC, we need μHz sensitivity!

Chu: Atom Interferometer Use 4 π/2 Raman pulses Creates 2 Atom Interferometers Sensitivity Limited by Phase number of photon Recoils…

Chu’s Clever Trick Adding N (here N=2) π-pulses allows for N times greater recoil shift.

Results 7.7 ppb UC Problems Recoil Efficiency = 94% Recoil Efficiency = 94% Allows other Zeeman sublevels to be populated N recoil <60 N recoil <60

Clade: Bloch Oscillations in Optical Lattice 1.Laser Cooling in a MOT down to 3 mK, 2.As in Chu expt, there is a π pulse pumping atoms of particular velocity class into F=1, 3.Force N Bloch Oscillations using Optical Lattice to build up atom recoil momentum 4.Another π pulse tuned to F=1 -> F'=2 to measure final velocity via TOF.

Bloch Oscillations: Tilted Lattice Marble would fall (classically), but atom-waves oscillate! Periodicity of Bloch solutions requires the oscillations

Creating the Constant Force Could use gravity or E-field These are undesirable These are undesirable Solution: Sweep the frequency of one of the lasers in the Standing Wave! Wave only “stands” in accelerated reference frame Wave only “stands” in accelerated reference frame Think of nodes/antinodes moving accelerating down the line as the frequency is swept

Apparatus

Results 6.7 ppb (Chu 7.7 ppb) g-2 record is 3.9 ppb, Gabrielse et. al. g-2 record is 3.9 ppb, Gabrielse et. al. Recoil Efficiency: 99.7% (Chu 94%) N recoil ~ 900 (Chu 60)