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Measuring the Electron EDM Using Ytterbium Fluoride (YbF) Molecules
Joe Smallman
“measuring the shape of the electron”
2
The electron electric dipole moment (EDM)
• Displacement of centre of charge from centre of mass
�⃗�
𝑈=− �⃗�𝑒 ∙𝐸
−−−−−
−−
�⃗�𝑒 ǁ𝜎
�⃗�𝑒
3
Electron EDM estimates
|dethallium|< 1.6 x 10-27e.cm
David A. AguilarHarvard-Smithsonian Center for Astrophysics
not enough CP violation
4
How small is that?
• Assume:
• for magnetic field
− �⃗�𝑒 ∙ �⃗�≈0.25𝑚𝐻𝑧EDM interaction:
5
How atoms and molecules can help
• Amplify the electron EDM interaction!
− �⃗�𝑒 ∙ �⃗�complicated
special relativity − �⃗�𝑒 ∙ �⃗�eff
�⃗� eff=𝐸effmaxη (𝐸app ) �̂�
structure dependent
factor
polarisationfactor
�⃗�𝑒
𝐸app �̂�
�̂�
6
YbF electric field enhancement
• for • Enhancement of
• Needs ‘only’ nano-Gauss level of B-field control
7
YbF energy levels
8
EDM measurement
ϕ=(μ B∓d¿¿ e Eeff )Tħ
¿∆𝜙<7 μrad
∆𝑈<2mHzor
�⃗�
𝜙
�⃗� eff
�⃗�
Torque:
9
Measuring the electron EDM
10
Interference fringes
𝑆=cos2ϕ ϕ=(μ B∓d¿¿ e Eeff )Tħ
¿
11
Lots of other parameter modulations
• E-field direction• B-field direction• B-field magnitude• rf pulse frequency (independently)• rf pulse amplitude (independently)• rf pulse phase difference• laser frequency
demonstrated in last slide
12
Result
d e=(−2.4±5.7stat±1.7s yst )×10−28 e . cm
J J Hudson et al. Nature 473 493-496 (2011)D M Kara etal. New. J. Phys. 14 103051 (2012)
with 90% confidence
• 2011 dataset: 6194 measurements (6min/measurement)
13
Upgrades since 2011
• 3rd layer of magnetic shielding• Less magnetic field noise
• Longer inner magnetic shield• Reduce end effects
• Separate rf transmission line from HV plates• Reduce end effects, higher applied E-field, less leakage
• Shorten rf pulses• Reduce systematics associated with rf detuning
old scheme new scheme
14
YbF fountain
• 0.5s coherence time instead of 0.5ms e cm
in 8hrs
Tarbutt et al. New J. Phys. 15 053034 (2013)
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The YbF eEDM team
Jony Hudson
Ben SauerJoe Smallman
Jack Devlin
Mike Tarbutt Ed Hinds
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EDM measurement
F=1
F=0
mF=-1
nuclear spin electron spin
mF=0mF=+1
mF=0
+
-
large tensor Stark shift
• Measure the EDM induced splitting