Presentation on theme: "Cold and slow molecular beams: Application to electron electric dipole moment (EDM) measurements Katsunari Enomoto, Univ. of Toyama Fundamental Physics."— Presentation transcript:
Cold and slow molecular beams: Application to electron electric dipole moment (EDM) measurements Katsunari Enomoto, Univ. of Toyama Fundamental Physics Using Atoms /Aug/9 Osaka U.
Electron electric dipole moment spin EDM electron T, P Standard model electron EDM SUSY, left-right, multi-Higgs Experiment (Tl atomic beam) Table-top experiment for the physics beyond the standard model. d e e cm d e < e cm d e < e cm PRL 88, (2002). related with CP, T violation physics
EDM measurement using atoms Due to the relativistic effect, heavy atoms have large enhancement factor R. Typical atomic beam method E appl 0.1 MV/cm B 1 nT S E // B E // B precession I False EDM signal (systematic error) Leak current loop v E induced field v E (Cs: R 110, Tl: R 590, Fr: R 1150) E eff = R E appl 0.1 GV/cm, d e E eff / h 10 Hz t m= 1/2 m=1/2 BB hh or
EDM measurement using molecules atom mix with E appl elec. molecule Induced dipole E eff = R E appl 0.1 GV/cm, with E appl 0.1 MV/cm mix with E appl rot. E eff = P E mol 10 100 GV/cm, P 1 with E appl 0.01 MV/cm (E appl is needed just for aligning molecule) E mol permanent dipole E eff |s |p |J=0 |J=1 Sensitivity 100 1000 Systematic error 0.1
Atoms vs molecules Tl beam experimentYbF beam experiment PRL 88, (2002).PRL 89, (2002). d e < e cmd e < 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. vs
Ultracold molecules Ultracold molecules are one of the hottest topics in atomic/molecular/optical (AMO) physics in this decade. High resolution spectroscopy Test of fundamental physics Ultracold chemistry Control of chemical reaction New condensed matter Quantum simulator Laser cooling of atoms and associating to molecules ( nK) Direct cooling of molecules ( mK)
Direct cooling methods (1) Supersonic expansion is a conventional method for molecular spectroscopy, and it generates cold ( 1 K) but fast (supersonic) molecular beams. Stark decelerator & electrostatic trap Bethlem et al., Nature 406, 491 (2000). Gupta et al, J. Phys. Chem. A 105, 1626 (2001) Counter-rotating nozzle How to slow down?
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)
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.
Microwave trap for molecule DeMille et al, Eur. Phys. J. D 31, 375 (2004) It has been proposed to a microwave field enhanced in a Fabry-Perot cavity to trap polar molecules. For static field (dc Stark shift) For microwave field (ac Stark shift) Assuming power P 2 kW, quality factor Q 10 5, Electric field E 30 kV/cm ( 3 K trap depth) is possible. 2B: rotational splitting : detuning d : dipole moment of molecule (J=0,1 states) Electric field E (P Q) 1/2
Microwave Stark decelerator Enomoto & Momose, PRA 72, (2005) We proposed that HFS state molecules can be decelerated by using time-varying standing wave of microwave. Potential w/ microwave Current plan: to use circular waveguide resonator TE 11 mode Potential w/o microwave TE 11 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)
Simulation of deceleration Microwave Stark decelerator can be used for molecular beams pre-cooled to about 5 K. Molecule : 174 YbF Initial velocity : 21 – 24 m/s Center molecule : 22.5 m/s (5.8 K) Deceleration : 93 cm, 80 ms P[W] Q : 10 7
First experimental step: microwave lens Odashima et al., PRL 104, (2010) Performed in Fritz-Haber institute by using a decelerated NH 3 beam w/o microwave w/ microwave Molecular beams can be focused with a microwave field.
Next plan for microwave control Electric field E 2 (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. We will test the superconducting cavity soon in U. British Columbia (Momose lab.) (Q factor is mainly determined by the surface resistance.) Power P[W] 3 < 3 ? Q-factor 5000 3 10 6 ? P Q 1.5 10 4 10 7 ? 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 > 10 6 is typically easily obtained, but we have to rapidly switch microwave. This limits the Q factor.
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 We will test a Pb/Sn-coated superconducting cavity soon. Q L 5000 Q L Cool down with L.N2 Q factor 3
Project in Univ. of Toyama We are making cold molecular beams based on He buffer-gas cooling. We have observed Pb and O atoms produced by laser ablation of a PbO target with mass spectrometer. To mass spectrometer Laser ablation (pulsed green laser) exit hole sorption pump He gas line L. He bath
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 Heavy atom Large electro- negativity 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, E eff = 26 GV/cm) or BaF (E eff = 8 GV/cm) unpaired electron
Cooling procedure Supersonic jet Initial velocity is determined by carrier gas 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) Effusive He buffer-gas-cooled beam Initial velocity is determined by the cell temperature ( 4 K) room T 4 K, high He density 4 K, low He density density and directionality high low We will use He buffer-gas-cooled beam close to effusive regime.
Improvement of flux How to generate molecules? Laser ablation /pulse poor reproducibility Injection from oven oven /s ? (like J. Doyle group) Future possibility Microwave deceleration and trap Combination of alternate gradient decelerator and microwave decelerator How to improve directionality? Microwave lens Laser cooling (SrF: Shuman et al., PRL 103, (2009).) They also help isotope selection suppression of background noise
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. 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. Odashima et al., PRL 104, (2010)
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
4K shield 77K shield 分子ビーム チャコール セル
マイクロ波定在波 TE 11 TE 01 Fabry-Perot TEM 00 マイクロ波定在波なし マイクロ波定在波あり
Q-massL. HeHe gas pulse YAG 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
Bethlem et al., PRA 65, (2002). LFS HFS
Stark Buffer gas Microwave Cold slow beam Lens (collimation) decelerationtrap EDM measurement UBC Toyama
Acknowledgment FHI UBC Toyama
Atoms or molecules? atom molecule Experiment (Tl atomic beam) d e < e cm Experiment (YbF molecular beam)d e < e cm Cold molecular beam (or trapped molecules) will improve much more. Easy to handle High electric field E appl is needed (causing systematic error) E eff 500 E appl, E appl 100 kV/cm Large internal electric field (E eff 10 GV/cm) Rotation and vibration exist (small population in the ground state at room temperature, which reduce statistical certainty) rot. vib. mix with E appl to align molecule mix with E appl elec. PRL 88, (2002). PRL 89, (2002). Induced dipole