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