Transcript 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…
Electronic Kg
• Balance Gravity
Force with EMF
• Find value for h,
Planck’s Constant
•Deduce me from:
2R h
me
c
2
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.
1997
Measuring mp/me and MAtom/mp
Penning Trap

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%
Allows other Zeeman sublevels to be populated

Nrecoil<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
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
Apparatus
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)