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Precision α Measurement: Atom Recoil Method Review

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 Methods using g-2 involve lengthy QED equations which undergo frequent revision Working Toward an Electronic Kilogram….

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Precision α Measurement: Atom Recoil Method Review

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

  2. Motivation • 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…

  3. Electronic Kg • Balance Gravity Force with EMF • Find value for h, Planck’s Constant • Deduce me from:

  4. Physical Constant Uncertainties:

  5. 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. 1997 • Measuring mp/me and MAtom/mp

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

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

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

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

  10. Results • 7.7 ppb UC • Problems • Recoil Efficiency = 94% • Allows other Zeeman sublevels to be populated • Nrecoil<60

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

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

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

  14. Apparatus

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

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