1. Katsunari Enomoto, Univ. of Toyama
Cold and slow molecular beams: Application to electron electric dipole moment (EDM) measurements
富山大の…。低温低速分子ビームを用いた…。今年からこの新学術…。極低温分子気体…AMO…。
Katsunari Enomoto, Univ. of Toyama
Fundamental Physics Using Atoms /Aug/ Osaka U.

2. Electron electric dipole moment
spin
spin
EDM
T, P
electron
EDM
related with CP, T violation physics
Standard model electron EDM
de  e cm
３日目ですので…。電子にEDMがあるとT,P-violation…。標準模型の範囲では…。その先にあるSUSYなどの模型…。いくつかのパラメータ範囲は…。このように標準模型を超えた…。
SUSY, left-right, multi-Higgs
de < e cm
Experiment (Tl atomic beam)
de < e cm
PRL 88, (2002).
Table-top experiment for the physics beyond the standard model.

3. EDM measurement using atoms
E // B
Typical atomic beam method
E // B or S
precession
Eappl0.1 MV/cm
B1 nT
 t
Due to the relativistic effect, heavy atoms have large enhancement factor R.
(Cs: R110, Tl: R590, Fr: R1150)
h B
典型的な…。偏極した原子…強い電場と弱い磁場…平行・反平行…歳差運動周波数の差をみる。相対論的効果により…。放電を起こさない程度の電場…0.1MV/cmなので、例えばこれにFrのenhancement factorをかけたものE_effectiveは0.1GV/cm程度です。また、系統誤差の原因となる偽のEDM…。
Eeff = R Eappl  0.1 GV/cm,
  de Eeff / h  10 Hz
m=1/2
m=1/2 I
False EDM signal (systematic error)
Leak current loop
v  E induced field v E

4. EDM measurement using molecules
atom
molecule
Induced dipole
permanent dipole
|p
mix
with
Eappl
|J=1
mix
with
Eappl
Eeff
Emol
rot.
|J=0
elec.
|s
Eeff = R Eappl  0.1 GV/cm,
with Eappl  0.1 MV/cm
Eeff = P Emol  10100 GV/cm,
P  1 with Eappl  0.01 MV/cm
(Eappl is needed just for aligning molecule)
我々が目指しているのは分子を用いたEDM測定ですが、ここで原子と電子を比べてみます。実効的電場E_effは先ほどの例の通り、100kV/cmにR=1000をかけて0.1GV/cmです。一方、分子の場合分極による内部電場があり、分子を外場によって偏極させることで、その強い内部電場を利用できます。実効的電場E_effはalignmentの度合いPに分子固有の値E_molをかけたものになり、E_molは数十GV/cm程度です。
Sensitivity  1001000
Systematic error  0.1

5. Atoms vs molecules Tl beam experiment YbF beam experiment vs
PRL 88, (2002). vs
PRL 89, (2002).
de < e cm
de < e cm
Why is it not so good?
…. because radical molecular beams
are difficult to produce,
and molecules have
many internal levels
(especially rotation).
Vibration (1000 K)
Rotation
( 1K)
Cold (large population in the ground state) and slow (long interaction time)
molecular beam will improve greatly the sensitivity.
In this talk, after reviewing cold molecule experiments,
I will present our recent results and ongoing projects.

6. Ultracold molecules Direct cooling of molecules (mK)
Ultracold molecules are one of the hottest topics in
atomic/molecular/optical (AMO) physics in this decade.
High resolution
spectroscopy
New
condensed matter
Test of fundamental
physics
Quantum simulator
Ultracold
chemistry
Direct
cooling of
molecules
(mK)
Laser cooling
of atoms and
associating to
molecules (nK)
Control of chemical
reaction

7. Direct cooling methods (1)
Supersonic expansion is a conventional method for molecular spectroscopy,
and it generates cold (1 K) but fast (supersonic) molecular beams.
How to slow down?
Stark decelerator & electrostatic trap
　　Bethlem et al., Nature 406, 491 (2000).
Gupta et al,
J. Phys. Chem. A 105, 1626 (2001)
Counter-rotating nozzle

8. Direct cooling methods (2)
Laser ablation can generate molecular gases in
cryogenic helium gas (1 K).
Buffer-gas cooling & magnetic trap
Weinstein et al., Nature 395, 148 (1998)
Effusive molecular beam
Hydrodynamically enhanced-flux
(but boosted to 160 m/s)
molecular beam
Maxwell et al., Phys. Rev. Lett. 95, (2005)
Patterson et al., J. Chem. Phys. 126, (2007)

9. Control of translational motion
Now, molecules can be cooled/decelerated down to 1 K.
Many tools are available to control molecular translational motion,
e.g. electric & magnetic static field, optical field, …
Our approach: using microwave field
Advantage of microwave:
High-field-seeking (HFS)
ground state can be trapped.
Stark shift of diatomic molecules
DeMille et al, Eur. Phys. J. D 31, 375 (2004)
HFS state cannot be trapped with
static fields due to Earnshaw’s theorem.

10. Microwave trap for molecule
It has been proposed to a microwave field enhanced in a Fabry-Perot
cavity to trap polar molecules.
For static field (dc Stark shift)
(J=0,1 states)
For microwave field (ac Stark shift)
DeMille et al, Eur. Phys. J. D 31, 375 (2004)
2B: rotational splitting
: detuning
d : dipole moment of molecule
Electric field E  (P  Q)1/2
Assuming power P 2 kW, quality factor Q 105,
Electric field E  30 kV/cm ( 3 K trap depth) is possible.

11. Microwave Stark decelerator
We proposed that HFS state molecules can be decelerated
by using time-varying standing wave of microwave.
Enomoto & Momose, PRA 72, (2005)
Potential
w/ microwave
Current plan: to use circular waveguide resonator TE11 mode
w/o microwave
TE11
Radial confinement
for HFS state
Alternate gradient focusing decelerator
Bethlem et al., PRL 88, (2002)
More powerful,
but dynamical radial confinement
Tarbutt et al., PRL 92, (2004)

12. Simulation of deceleration
Molecule : 174YbF
Initial velocity : 21 – 24 m/s
Center molecule : 22.5 m/s (5.8 K)
Deceleration : 93 cm, 80 ms
P[W]  Q : 107
Microwave Stark decelerator can be used for molecular beams
pre-cooled to about 5 K.

13. First experimental step: microwave lens
w/o microwave
Molecular beams can be
focused with a microwave
field.
w/ microwave
Odashima et al., PRL 104, (2010)
Performed in Fritz-Haber institute by using a decelerated NH3 beam

14. Next plan for microwave control
Electric field E2  (power P)  (quality factor Q)
High P needs expensive amps and causes heating.
So we are planning to use a superconducting cavity for high Q.
(Q factor is mainly determined by the surface resistance.)
Power P[W] < 3 ?
Q-factor 3106 ?
P  Q  107 ?
Lens exp.
(Cu cavity)
SC cavity
(Nb or Pb/Sn)
Limited by cooling power
(Note that only 0.1 s is
needed for deceleration.)
Q > 106 is typically easily
obtained, but we have to
rapidly switch microwave.
This limits the Q factor.
We will test the superconducting cavity soon in U. British Columbia
(Momose lab.)

15. Project in Univ. of British Columbia
We are constructing a Stark decelerator in UBC.
We will combine the Stark decelerator with superconducting cavity.

16. Testing a microwave resonator
Firstly, we tested a copper resonator
with a loop antenna.
loop antenna
QL  5000
QL  16000
Cool down
with L.N2
Q factor
 3
We will test a Pb/Sn-coated superconducting cavity soon.

17. Project in Univ. of Toyama
We are making cold molecular beams based on He buffer-gas cooling.
L. He bath
He gas
line
To mass
spectrometer
exit hole
Laser ablation
(pulsed green laser)
sorption
pump
We have observed Pb and O atoms produced
by laser ablation of a PbO target with mass spectrometer.

18. EDM measurement project
We are starting the EDM measurement project in Univ. of Toyama
from this year.
Only the project plan is presented here.
What molecules?
How to produce molecules?
How to cool them to a few K?
How to enhance the flux?
What more?

19. Choice of molecule To obtain high beam flux in a single internal state
unpaired
electron
Large
electro-
negativity
Heavy atom
To obtain high beam flux in a single internal state
Low boiling point (even for laser ablation)
Small nuclear spin (simple hyperfine structure)
large natural abundance
From experimental point of view
Less toxic
Not radioactive
Tentative plan: to use YbF (like E. Hinds group, Eeff = 26 GV/cm)
or BaF (Eeff = 8 GV/cm)

20. Cooling procedure Supersonic jet high
Initial velocity is determined by
carrier gas
room T
e.g. YbF in Xe
300 m/s corresponds to 1000 K for YbF
Hydrodynamic He buffer-gas-cooled beam
Initial velocity is determined by
He gas (160 m/s  300 K for YbF)
density and directionality
4 K, high He density
Effusive He buffer-gas-cooled beam
Initial velocity is determined by
the cell temperature ( 4 K)
low
4 K, low He density
We will use He buffer-gas-cooled beam close to effusive regime.

21. Improvement of flux How to generate molecules?
Laser ablation
Injection from oven
oven
1012 /pulse
poor reproducibility
1015 /s ?
(like J. Doyle group)
How to improve directionality?
Microwave lens
Laser cooling (SrF: Shuman et al., PRL 103, (2009).)
They also help isotope selection  suppression of background noise
Future possibility
Microwave deceleration and trap
Combination of alternate gradient decelerator and microwave decelerator

22. Conclusion Microwave enhanced in resonators is available to control
molecular translational motion (such as deceleration and trap).
As a first step, we demonstrated the microwave lens.
Odashima et al., PRL 104, (2010)
We will test soon a high-Q superconducting resonator.
For electron EDM measurement, we are making He-buffer-gas-
based cold molecular beam (YbF or BaF).
EDM measurement with molecular beams with cold molecule
technologies developed in this decade is promising.

23. Acknowledgments Microwave lens experiment
H. Odashima, S. Merz, M. Schnell, G. Meijer (Fritz-Haber-Institut)
Superconducting cavity project
O. Nourbakhsh, P. Djuricauin, T. Momose,
W. Hardy and his students (Univ. of British Columbia)
Buffer-gas cooled beam project
Y. Kuwata, H. Noguchi, H. Hasegawa, S. Tsunekawa,
K. Kobayashi, F. Matsushima, Y. Moriwaki (Univ. of Toyama)
And courtesy of D. DeMille

26. 77K shield
分子ビーム
4K shield
チャコール セル

27. マイクロ波定在波
TE11
TE01
マイクロ波定在波あり
マイクロ波定在波なし
Fabry-Perot
TEM00

28. Q-mass L. He He gas pulse YAG Diode laser J=1 J=0 B state J’=1 X state
PbO
Diode
laser
pump
J=1
J=0
B state
J’=1
シュタルク
ガイド
マイクロ波
トラップ
光ポンピング
X state

29. LFS
HFS
Bethlem et al., PRA 65, (2002).

30. Stark
UBC
Microwave
Lens
(collimation)
deceleration
trap
Buffer gas
Cold slow beam
EDM measurement
Toyama

31. Acknowledgment
FHI
UBC
Toyama

32. Atoms or molecules? atom molecule Experiment (Tl atomic beam)
vib.
atom
molecule
Induced dipole
mix
with
Eappl
elec.
rot.
mix with Eappl
to align molecule
Large internal electric field
(Eeff  10 GV/cm)
Easy to handle
High electric field Eappl is needed
(causing systematic error)
Eeff  500 Eappl, Eappl  100 kV/cm
Rotation and vibration exist
(small population in the ground state
at room temperature, which reduce
statistical certainty)
Experiment (Tl atomic beam)
de < e cm
PRL 88, (2002).
Experiment (YbF molecular beam)
de < e cm
PRL 89, (2002).
Cold molecular beam (or trapped molecules) will improve much more.