Transcript Unusually large polarizabilities of excited states of Ba

Experimental Atomic Physics
Research in the Budker Group
• Tests of fundamental symmetries using
atomic physics:
• Parity
• Time-reversal invariance
• Permutation Postulate/Spin-Statistics Connection
• Temporal variation of fundamental “constants”
• Applied atomic spectroscopy
• Sensitive magnetometry and electrometry
• Nonlinear optics with atoms
• Optical properties of superfluid helium
• “New” atomic energy levels
• Properties of complex atoms: the rare earths, Ba
Group Demographics and
Philosophy
•
6 graduate students
•
1 - 3 undergrads
•
2 staff scientists (1 senior, 1 junior)
•
Part-time technician
•
Lots of visitors from US and abroad
•
Each student has their own project
•
Lots of interactions within group
•
Variety of experiences and techniques: lasers, optics, atomic beams
and vapor cells, cryogenics, computer control and data acquisition,
vacuum, electronics, theory, scientific writing and editing, …..
Further information:
• http://socrates.berkeley.edu/~budker
• [email protected]
• Office: 273 Birge; labs:
217,219,221,230,241, and 245 Birge
Atomic Parity Nonconservation
e
e
g
Z
Electromagnetic
interaction
(conserves parity)


 ( r ) =  ( r )
Weak
interaction
(violates parity)


 ( r )   ( r )
 Small Modifications of the Optical Properties of
Atoms
Provides Unique Low-Energy Test of the
PNC Experiments
Electric and magnetic fields define a handedness
PNC effects show up as dependence of atom-photon
interaction on handedness
Photo-multiplier tubes
Oven
Collimator
Ytterbium
atoms
Light
guide
PBC mirror
y
z
E
e
x
B
408-nm light
Electric field plates
Parabolic
reflector
649-nm light
Magnetic field coils
Two Experiments in Progress: Dysprosium (Z=66) and
Ytterbium (Z=70)
How constant is the
fine structure
“constant” a?
EXPERIMENTAL
Astrophysical:
THEORETICAL
Theories that unify gravity
with other forces either
allow or necessitate a variation
Geophysical:
Oklo natural nuclear reactor
1.8 billion years ago:
.
-18
|a/a| < 10
/yr
Laboratory:
•H-maser vs. Hg+ microwave clock:
.
-14
a/a < 3.7  10
.
a/a = (-7.2  1.8)  10-16 /yr
[J. K. Webb, et al. , Phys. Rev. Lett.
87, 091301 (2001).]
/yr
•Rb vs. Cs microwave clocks:
.
-14
|a/a| < 1.1  10
/yr
•Hg+ optical vs. Cs microwave clocks:
.
-15
|a/a| < 1.2  10
/yr
.
a in dysprosium
A
B
n ~
Energy (cm-1)
20,000
levels A and B are highly
sensitive to
3-2000 MHz
variations
in a
0
nn’
.
.
n ~ 21015 Hz |a/a|
.
i.e. for |a/a| ~ 10-15 /yr
.
 n ~ 2 Hz/yr
Ground State
rf freq.
generator
atomic freq.
standard
E-field plates
atomic beam
NONLINEAR MAGNETO-OPTICAL ROTATION
Goal: Obtain highest possible sensitivity to magnetic fields.
F’ = 0
Use laser light to polarize atoms:
(1) Aligns magnetic dipole moments;
(2) Creates preferred optical axis.
F=1
MF = -1
MF = 0
MF = +1
Magnetic moments precess in magnetic field:
Optical axis rotates 
causes light polarization to rotate.
 =
gFmB/grel
1 + (gFmB/grel)2
Paraffin-coated cells smuggled
in as Christmas ornaments!
(For FSB agents: this is a joke!)
10
grel ~ 1 Hz
DB ~ 1 mG ~ 0.1 nT
6
Rotation Angle (mrad)
Slow relaxation of
atomic polarization:
8
4
2
0
-2
-4
-6
-8
-10
-1.0
-0.8
-0.6
-0.4
-0.2
-0.0
0.2
Magnetic Field (nT)
0.4
0.6
0.8
1.0
Pumping and probing with FM light
FM NMOR magnetometry: Phys.Rev.A65, 055403 (2002)
Precision magetometry and atomic EDM measurement
using spin-polarized atoms in a buffer gas at cryogenic
temperatures
• Problem: to measure very small B; to measure electron EDM
• Paramagnetic atom magnetometer; He buffer gas at T=4K to
increase spin-relaxation time to minutes
Measuring the Kerr effect in LHe and the LANL neutron
EDM experiment
• Problem: to measure strong electric fields (50kV/cm) inside
a bath of LHe at 300mK.
• Kerr effect: an initially isotropic medium acquires
birefringence when electric field is applied, measure this.
241 Birge, midnight, 8/25/03
Neutron EDM experiment at LANSCE
Light Guides
Cells Between
Electrodes
HV and Ground
Electrodes
Beam Entrance
Window
Cosq Coil
SQUID Enclosure
HV Variable Capacitor
Laser spectroscopy for
fundamental symmetry tests
Motivation: BEV exp
Lifetimes, branching ratios, new levels,
polarizabilities (Ba)
Unusually large polarizabilities
(100 times; for n<10, only smaller than 2s,2p of H)
“new” opposite-parity levels
Electron EDM exp
Noncontact circuit board testing
Probed States
Laser Excitation
559 - 569.5 nm
Fluorescence
~ 435 nm
6s6p 1P1
6s6p 3P0,1,2
Laser Excitation 554.7 nm
6s2 1S0
Even Parity
Odd Parity
What is the experiment?
A test of the spin statistics theorem (SST) for photons.
What is the SST?
Barium
How we do it
Interaction region
Power Build-up Cavity
Oven Housing w/Collimator
1.04"
0.28"
1.58"
0.95"
0.70"
0.82"
1.22"
1.70"
Chamber
Numbers
Experimental Atomic Physics
Research in the Budker Group