Nuclear spin maser with a novel masing mechanism and its application to the search for an atomic EDM in 129 Xe

Transcription

1 Nuclear spin maser with a novel masing mechanism and its application to the search for an atomic EDM in 129 Xe A. Yoshimi RIKEN K. Asahi, S. Emori, M. Tsukui, RIKEN, Tokyo Institute of Technology

2 Nuclear polarization of noble gas atoms Noble gas atoms with nuclear spin I = 1/2 3 He, 129 Xe 3 He, 21 Ne, Ar, Kr, Xe, Rn J = 0 Application to fundamental physics Large polarization long relaxation time 129 Xe: Polarization P O(10-100) torr Relaxation: T 1 20 min. 3 He: Polarization P atom Relaxation : T 1 40 hours. I 0 T-violation MRI with polarized 3 He Fundamental physics: Test of time-reversal symmetry (EDM) High-energy physics: Investigation of neutron spin structure Surface physics: Enhancement of NMR signal Medical application: MRI Quantum computer T.Walker et al., Rev. Mod. Phys. 69 (1997) 629.

3 Electric Dipole Moment (EDM) and T-violation Non-zero EDM associated with spin implies violation of time reversal symmetry s s Time reversal Time: t -t Spin: s -s EDM: d d d 0 T-violation CP-violation Standard Model (SM) : Predicted EDM is about 10 5 smaller than the present experimental upper limit Beyond the SM : Detectable EDM Detection of non-zero EDM CP-violation beyond standard model

4 Neutron 26 d n < ecm P.G. Harris et al., PRL 82(1999) 904. Measurement of precession frequency shift B E B E Diamagnetic atom CP-violating nucleon-nucleon interaction 199 Hg Washington Univ. d(hg) < e cm M. Romalis et al., PRL 86 (2001) ω + = 2 µ B + 2dE h ω + ω 2µ B 2dE ω = h 4dE = h 129 Xe Washington Univ., Michigan Univ. d(xe) < e cm M. Rosenberry and T. Chupp, PRL86(2001) 22. Paramagnetic atom Electron s EDM 133 Cs, 205 Tl, Standard model (SM) : d(xe) = ecm d n = ecm Supersymmetric model : d(xe) = ecm (naturally)

5 Project of atomic EDM experiment of 129 Xe at RIKEN-TIT Large polarization of Xe nucleus Rb Spin exchange with optical pumped Rb atom Nuclear polarization O(10) 100 torr (10 18 /cc) 129 Xe Continuous nuclear spin maser with low frequency Free Induction Decay Continuous oscillation 1/ 2 σ ν τ 3/ 2 σ ν τ Rapid decrease of frequency precision Optical detection of nuclear spin precession Low static field experiment ( mg ) Small field fluctuation Use of the ultra high sensitive magnetometer

6 Nuclear polarization of 129 Xe by optical-pumping spin-exchange Atomic polarization of Rb by optical pumping W. Happer, Rev. Mod. Phys. 44 (1972) 169. Selective excitation by circular polarized light 5P 1/ 2 D1 line : nm 5S 1/ 2 m s 1 = 2 m s 1 = + 2 Polarization transfer from Rb atom to Xe nuclei through hyperfine interaction Two body collision with Rb atom Formation of van der Waals molecule with Rb

7 Xe cell Cleaning baking Coating Rb Xe confinement Coating agent : SurfaSil suppression of the spin relaxation of Xe Glass cell φ 20 mm Xe 10 2 torr Rb mg Spin relaxation: due to wall collision Non-coating: T W 3 min. Coated cell: T W 20 min. P = 69.4 ± 1.9 Xe 100 torr

8 Spin maser Transverse magnetic field - synchronism with spin precession - Phase : perpendicular to the transverse polarization Amplitude : proportional to the transverse polarization Polarization s growing (pumping effect) Relaxation, pumping B 0 T2 relaxation Feedback torque Polarization vector : M Feedback torque Polarization Feedback field : B fb Population inversion Feedback EM-field synchronism with emitted photon pump Zeeman level Feedback system

9 NMR-based spin maser Spin maser with the tuned coil of tank circuit Optical-detection-feedback spin maser Artificial feedback through the optical spin detection B FB L B 0 Probe laser beam B 0 mg Feedback coil Phase shifter Induced current I npq Pumping light γ B C 0 = 1 LC Nuclear spin Pumping laser beam Photo diode Lock-in detection Oscillation threshold 1 γ ηµ 0Q hinp0 > T2 ν > khz (B 0 = 1 G) Operation at low magnetic field Small field fluctuation High-sensitive magnetometer Long intrinsic T 2

10 Optical detection of 129 Xe nuclear precession Transverse-polarization transfer : Rb atom Xe nuclei (re-polarization) Rb Xe dp dt Rb = γ se( PXe PRb ) ΓsdP = γ '[ Xe]( P ) Rb Xe PRb ΓsdPRb γ [Xe] = /s, Γ sd = 0.2 /s Time constant of spin transfer: 10-4 s Precession frequency of < khz P Rb Probe laser beam : single mode diode laser (794.7nm) 0.3 ms (ms) Xe After half-period precession Xe Circular polarization (modulated by PEM) Xe Rb Xe Xe Rb Xe

11 Experimental apparatus Pumping LASER Tunable diode laser λ = nm ( Rb D1 line ), λ = 3 nm Output: 18 W Solenoid coil (for static field) B 0 = 28.3 mg ( I = 3.58 ma) Magnetic shield (3 layers ) Permalloy Size : l = 100 cm, d = 36, 42, 48 cm Shielding factor : S = 10 3 Si photo diode Freq. band width: khz NEP: W/Hz Probe LASER Heater T cell = 60 ~ 70 PEM Mod. Freq. 50 khz Xe gas cell 18 mm Enriched 129 Xe : 230 torr Rb : ~ 1 mg P xe ~ 10 % Pyrex spherical grass cell SurfaSil coated Tunable diode laser with external cavity λ = nm ( Rb D1 line ), λ = 10-6 nm Output: 15 mw

12 Feedback system Producing the feedback field delayed by 90 in phase to precession signal Low pass filtering ( f cut ~ 0.8 Hz ) Reconfiguration of precession correlated signal High S/N feedback signal Probe light Feedback coil 4 turns φ 20cm Modulated signal PEM Modul. Freq.(50 khz) 129 Xe Larmor Freq.(33.5 Hz) Pumping light Feedback field B FB = 1 γt 2 R = kω 3.6 µg 1 µg ( T 2 =100s) 1V Feedback signal (33.5 Hz) Si photo-diode PSD-signal (0.2 Hz) Operation circuit V Y V X Lock-in amp. Lock-in amp. φ = 0 φ = -90 ref. (50kHz) ref. ( 33.3 Hz ) Wave generator

13 LASER system Magnetic shield Around Xe cell Probe laser PEM Pumping laser Heater Xe cell Feedback coil

14 129 Xe free precession signal Static magnetic field: B 0 = 28.3 mg (ν(xe)=33.5 Hz) 90 RF pulse( 33.5 Hz, t = 3.0 ms, B 1 = 70 mg ) Transverse relaxation: T 2 = 350 s ; ( collision with Rb atoms field inhomogeneity ) Signal (mv) Time (s) Frequency: ν T s beat = ν prec ν ref = 0.23Hz

15 129 Xe spin maser signal B 0 = 28.3 mg, ν ref = Hz Feedback gain: 18 µg/0.1mv Signal (mv) Time (s) Steady state oscillation 0.1 Feedback system ON Measured frequency: ν beat = ν prec ν ref = 0.32Hz

16 Frequency characteristics Fourier spectrum ( 1 hr. run ) Artificial feedback spin maser ( ν = 33.5 Hz ) t (sec) φ (rad) ν = ± mhz Precession angle δν = 0.96 µhz Conventional spin maser ( ν = 3.56 khz ) Frequency precision (µhz) σ(ν) τ -3/ Time (s)

17 In-progress improvements; magnetic shield Construction of 4-layer shield l = 1600 mm, R= φ 400 mm Estimated shielding factor Transverse: S 10 6 Longitudinal: S 10 4 Measured Residual field z (cm) Field (μg) Bz

18 High-sensitive magnetometer in low frequency spin maser Fluctuation of magnetic field Main source of frequency noise in spin maser operation d atom ecm E =10 kv/cm δν 1nHz δb 1pG Neutron EDM experiment.. Hg atomic magnetometer Xe EDM Michigan Gr... 3 He co-magnetometer Atomic magnetometer with Rb using magneto-optical rotation D. Budker et al., PRA 62 (2000) k Linear polarized light Alkali vapor σ + σ - (F =0) B Faraday rotation rad/g, G/ Hz (B < 0.1G) m F = -1 m F = 0 m F = +1 (F=1) gµb

19 Estimation of experimental EDM-sensitivity Installation of atomic magnetometer into low frequency spin oscillator Conceptual setup sensitivity : G/ Hz δb G ( δν(xe) 0.1 nhz ) Main source of frequency noise interaction with Rb atomic spins (10 9 /cc) P(Rb) 0.01 % ( re-polarization from Xe ) ν(xe) 0.2 nhz (δt 0.01 C) (E=10kV/cm) Probe light (Magnetometer) d(xe) = ecm

20 Summary and Future Construction of the nuclear spin maser with an artificial feedback system, and operated it at low frequency 33 Hz ( under B = 28 mg ). Frequency precision of 1 contiguous measurement presently reach to 1 µhz. Construction of 4 layer magnetic shield. Installing the Rb magnetometer with magneto-optical rotation. Aiming at d(xe) = ecm.