Cold and slow molecular beams_ Application to electron EDM

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					Cold and slow molecular beams:
  Application to electron electric
  dipole moment (EDM)

     Katsunari Enomoto, Univ. of Toyama

 Fundamental Physics Using Atoms 2010   2010/Aug/9   Osaka U.
 Electron electric dipole moment

            spin                             spin
                                T, P

                                  related with CP, T violation physics

 Standard model               electron EDM de  10-38 e cm

 SUSY, left-right, multi-Higgs           de < 10-24 e cm

 Experiment (Tl atomic beam)             de < 10-27 e cm
                                                 PRL 88, 071805 (2002).

Table-top experiment for the physics beyond the standard model.
     EDM measurement using atoms
                                                                     E // B
Typical atomic beam method

                              or                                     E // B
 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
Eeff = R Eappl  0.1 GV/cm,   de Eeff / h  10 Hz
                                                         m=1/2 m=1/2
False EDM signal (systematic error)
              Leak current loop            v  E induced field

                          I                                      v

  EDM measurement using molecules

atom     Induced dipole             molecule       permanent dipole
                            mix                                |J=1   mix
Eeff                        with          Emol                         with
                            Eappl                      rot.    |J=0   Eappl
             elec.    |s
Eeff = R Eappl  0.1 GV/cm,           Eeff = P Emol  10100 GV/cm,
 with Eappl  0.1 MV/cm               P  1 with Eappl  0.01 MV/cm
                                    (Eappl is needed just for aligning molecule)

                     Sensitivity  1001000
                     Systematic error  0.1
               Atoms vs molecules
    Tl beam experiment                       YbF beam experiment
         PRL 88, 071805 (2002).      vs            PRL 89, 023003 (2002).

        de < 10-27 e cm                          de < 10-25 e cm

   Why is it not so good?            …. because radical molecular beams
             Vibration (1000 K)           are difficult to produce,
                                           and molecules have
                                           many internal levels
  Rotation                                 (especially 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.
      Ultracold molecules
    Ultracold molecules are one of the hottest topics in
    atomic/molecular/optical (AMO) physics in this decade.

      High resolution                    New
      spectroscopy                  condensed matter

    Test of fundamental             Quantum simulator
Direct                  chemistry         Laser cooling
cooling of                                of atoms and
molecules                                 associating to
(mK)                                     molecules (nK)
                   Control of chemical
   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        Counter-rotating nozzle
      Bethlem et al., Nature 406, 491 (2000).
                                                Gupta et al,
                                                J. Phys. Chem. A 105, 1626 (2001)
     Direct cooling methods (2)
                 Laser ablation can generate molecular gases in
                 cryogenic helium gas (1 K).

                                                  Effusive molecular beam
                                           Maxwell et al., Phys. Rev. Lett. 95, 173201 (2005)

                                                Hydrodynamically enhanced-flux
Buffer-gas cooling & magnetic trap
                                                (but boosted to 160 m/s)
Weinstein et al., Nature 395, 148 (1998)        molecular beam
                                           Patterson et al., J. Chem. Phys. 126, 154307 (2007)
  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

                                                           Stark shift of diatomic molecules
  Advantage of microwave:                                      LFS                J=1, m=0
    High-field-seeking (HFS)
    ground state can be trapped.

  DeMille et al, Eur. Phys. J. D 31, 375 (2004)                   HFS

                                                                                  J=1, |m|=1

 HFS state cannot be trapped with
 static fields due to Earnshaw’s theorem.                               Electric field
   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)
                                                                2B     dE / 3 
                                                            H 
                                                                dE / 3
                                                                          0  
                                                   For microwave field (ac Stark shift)
                                                                      dE / 2 3 
                                                          H                    
   DeMille et al, Eur. Phys. J. D 31, 375 (2004)                                 
                                                              dE / 2 3     0    
                                                        2B: rotational splitting
                                                        : detuning
    Electric field E  (P  Q)1/2                       d : dipole moment of molecule

   Assuming power P 2 kW, quality factor Q 105,
   Electric field E  30 kV/cm ( 3 K trap depth) is possible.
  Microwave Stark decelerator
   We proposed that HFS state molecules can be decelerated
   by using time-varying standing wave of microwave.
                                         Enomoto & Momose, PRA 72, 061403 (2005)

  Current plan: to use circular waveguide resonator TE11 mode


                                                              Radial confinement
                                                 Potential    for HFS state
  w/ microwave                                   w/o microwave

Alternate gradient focusing decelerator
      Bethlem et al., PRL 88, 133003 (2002)
      Tarbutt et al., PRL 92, 173002 (2004)
    More powerful,
    but dynamical radial confinement
  Simulation of deceleration                                                                                                               L


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                                                                                   200

                                                                                                        0     5        10   15        20   25
                  25                                                                                        Final velocity (m/s)
                  20                                                                     23.0

                                                                Initial velocity (m/s)
 Velocity (m/s)

                  10                                                                     22.8
                   0.0   0.2      0.4        0.6    0.8   1.0                            22.6
                  25            Distance (m)
                  20                                                                     22.4
                     0     20           40         60     80                             22.0
                                 Time (ms)                                                   -4                   -3             -2             -1
                                                                                                            Initial position (mm)
 Microwave Stark decelerator can be used for molecular beams
 pre-cooled to about 5 K.
First experimental step: microwave lens
                                         w/o microwave
Molecular beams can be
focused with a microwave
field.                                   w/ microwave

 Performed in Fritz-Haber institute by using a decelerated NH3 beam

                         Odashima et al., PRL 104, 253001 (2010)
  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.)

                 Lens exp.    SC cavity
                                                  Limited by cooling power
                (Cu cavity)   (Nb or Pb/Sn)
                                                  (Note that only 0.1 s is
Power P[W]           3            <3?              needed for deceleration.)

 Q-factor          5000        3106 ?           Q > 106 is typically easily
                                                  obtained, but we have to
 PQ             1.5 104        107 ?           rapidly switch microwave.
                                                  This limits the Q factor.

We will test the superconducting cavity soon in U. British Columbia
                                                   (Momose lab.)
 Project in Univ. of British Columbia
    We are constructing a Stark decelerator in UBC.

We will combine the Stark decelerator with superconducting cavity.
                 Testing a microwave resonator
                                                          Firstly, we tested a copper resonator
                                                          with a loop antenna.

                                                                                                         loop antenna

               1.0         QL  5000                   Cool down                  1.0     QL  16000
               0.8               room temperature
                                                       with L.N2                  0.8                 L. N2 temperature

                                                       Q factor                                       FWHM 1.07 MHz

                                 FWHM = 2.92 MHz
                                                            3                   0.6

               0.4                                                                0.4

               0.2                                                                0.2

               0.0                                                                0.0
                     785           790           795                                680         685              690
                           Frequency - 14000 (MHz)                                          Frequency - 16000 (MHz)

                     We will test a Pb/Sn-coated superconducting cavity soon.
Project in Univ. of Toyama
We are making cold molecular beams based on He buffer-gas cooling.

                                               L. He bath

                                     He gas
                          To mass

                                   exit hole
  Laser ablation
  (pulsed green laser)            sorption

   We have observed Pb and O atoms produced
   by laser ablation of a PbO target with mass spectrometer.
 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?
            Choice of molecule
        electron                          Large
                     Heavy atom           electro-

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)
                                          Cooling procedure
                         high     Supersonic jet
                                                             Initial velocity is determined by
                                 room T                      carrier gas
density and directionality

                                     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)
                                4 K, high He density

                                  Effusive He buffer-gas-cooled beam
                                                            Initial velocity is determined by

                                                            the cell temperature ( 4 K)
                                4 K, low He density

                      We will use He buffer-gas-cooled beam close to effusive regime.
           Improvement of flux
How to generate molecules?
      Laser ablation                      Injection from oven


         1012 /pulse                       1015 /s ?
         poor reproducibility               (like J. Doyle group)

How to improve directionality?
         Microwave lens
         Laser cooling   (SrF: Shuman et al., PRL 103, 223001 (2009).)

      They also help isotope selection  suppression of background noise
Future possibility
 Microwave deceleration and trap
 Combination of alternate gradient decelerator and microwave decelerator
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, 253001 (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.
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
77K shield


4K shield



   TE11        TE01

                        B state
                        J’=1    Diode
                                laser      マイクロ波
          J=1                              トラップ
                X state J=0

He       L. He                                 Q-mass

 pulse         pump            pump     シュタルク
 YAG                                    ガイド


Bethlem et al., PRA 65, 053416 (2002).
 Stark       UBC


                       Lens       deceleration   trap
Buffer gas         Cold slow beam                       EDM measuremen




  Atoms or molecules?
atom                                  molecule
             Induced dipole

             elec.                                        rot.
                                                                       mix with Eappl
                                                                       to align molecule
                                           Large internal electric field
        Easy to handle                     (Eeff  10 GV/cm)
High electric field Eappl is needed      Rotation and vibration exist
(causing systematic error)               (small population in the ground state
Eeff  500 Eappl, Eappl  100 kV/cm       at room temperature, which reduce
                                          statistical certainty)

  Experiment (Tl atomic beam)                          de < 10-27 e cm
                                                                 PRL 88, 071805 (2002).
  Experiment (YbF molecular beam)                      de <      10-25 e cm
                                                                 PRL 89, 023003 (2002).
 Cold molecular beam (or trapped molecules) will improve much more.

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