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
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 10-70 % @ O(10-100) torr Relaxation: T 1 20 min. 3 He: Polarization P 20-40 % @ 1-10 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.
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
Neutron 26 d n < 6.3 10 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) < 2.1 10 28 e cm M. Romalis et al., PRL 86 (2001) 2505. ω + = 2 µ B + 2dE h ω + ω 2µ B 2dE ω = h 4dE = h 129 Xe Washington Univ., Michigan Univ. d(xe) < 4.0 10 27 e cm M. Rosenberry and T. Chupp, PRL86(2001) 22. Paramagnetic atom Electron s EDM 133 Cs, 205 Tl, Standard model (SM) : d(xe) = 10 34 10 36 ecm 31 33 d n = 10 10 ecm Supersymmetric model : d(xe) = 10-27 10-29 ecm (naturally)
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
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 : 794.7 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
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
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
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 2 2 1 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
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] = 7 10 3 /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 0 0.4 0.8(ms) Xe After half-period precession Xe Circular polarization (modulated by PEM) Xe Rb Xe Xe Rb Xe
Experimental apparatus Pumping LASER Tunable diode laser λ = 794.7 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: 0 500 khz NEP: 8 10-13 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 = 794.7 nm ( Rb D1 line ), λ = 10-6 nm Output: 15 mw
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 = 10 50 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
LASER system Magnetic shield Around Xe cell Probe laser PEM Pumping laser Heater Xe cell Feedback coil
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) 0.2 0.0-0.2 0 100 200 300 400 500 600 Time (s) 0.16 0.00-0.16 100 110 120 Frequency: ν T 2 350 s beat = ν prec ν ref = 0.23Hz
129 Xe spin maser signal B 0 = 28.3 mg, ν ref = 33.20 Hz Feedback gain: 18 µg/0.1mv Signal (mv) 0.2 0.0-0.2 0 1000 2000 3000 4000 Time (s) Steady state oscillation 0.1 Feedback system ON 0.0-0.1 3000 3010 3020 Measured frequency: ν beat = ν prec ν ref = 0.32Hz
Frequency characteristics Fourier spectrum ( 1 hr. run ) Artificial feedback spin maser 0 0 5000 10000 ( ν = 33.5 Hz ) t (sec) φ (rad) 10000 ν = 277.20844 ± 0.00096 mhz Precession angle δν = 0.96 µhz Conventional spin maser ( ν = 3.56 khz ) Frequency precision (µhz) 100 10 1 0.1 σ(ν) τ -3/2 10 100 1000 Time (s)
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) 0-25 -15-5 5 15 25-20 Field (μg) -40-60 -80-100 Bz
High-sensitive magnetometer in low frequency spin maser Fluctuation of magnetic field Main source of frequency noise in spin maser operation d 10 28 atom ecm E =10 kv/cm δν 1nHz δb 1pG Neutron EDM experiment.. Hg atomic magnetometer Xe EDM experiment @ Michigan Gr... 3 He co-magnetometer Atomic magnetometer with Rb using magneto-optical rotation D. Budker et al., PRA 62 (2000) 043403. k Linear polarized light Alkali vapor σ + σ - (F =0) B Faraday rotation 1 10 4 rad/g, 4 10-12 G/ Hz (B < 0.1G) m F = -1 m F = 0 m F = +1 (F=1) gµb
Estimation of experimental EDM-sensitivity Installation of atomic magnetometer into low frequency spin oscillator Conceptual setup sensitivity : 10-11 10-12 G/ Hz δb 10-13 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) = 10 29 10 30 ecm
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) = 10-29 10-30 ecm.