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 3 He, 21 Ne, Ar, Kr, Xe, Rn Noble gas atoms with nuclear spin I = 1/2 Application to fundamental physics J = 0 3 He , 129 Xe I ≠ 0 Large polarization ・ long relaxation time 129 Xe: Polarization P ≈ 10 - 70 % @ O(10-100) torr T-violation Relaxation: T 1 ≈ 20 min. 3 He: Polarization P ≈ 20 - 40 % @ 1 - 10 atom MRI with polarized 3 He Relaxation : T 1 ≈ 40 hours. 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
Measurement of precession frequency shift − Neutron < × 26 d 6 . 3 10 e cm n B E B E P.G. Harris et al., PRL 82(1999) 904. Diamagnetic atom CP-violating nucleon-nucleon interaction 199 Hg Washington Univ. µ − µ + 2 B 2 dE 2 B 2 dE ω = ω = − + h 28 e h < × − d ( Hg ) 2 . 1 10 cm 4 dE ω − ω = M. Romalis et al., PRL 86 (2001) 2505. + − h 129 Xe Washington Univ., Michigan Univ. < × − 27 e M. Rosenberry and T. Chupp, PRL86(2001) 22. d ( Xe ) 4 . 0 10 cm Electron’s EDM Paramagnetic atom 133 Cs, 205 Tl, … − − − − = − − = 31 33 34 36 d 10 10 e cm Standard model (SM) : d ( Xe ) 10 10 e cm n Supersymmetric model : d( Xe ) = 10 -27 ∼ 10 -29 e cm (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 129 Xe Nuclear polarization O (10) % @ 100 torr (10 18 /cc) Continuous nuclear spin maser with low frequency Free Induction Decay Continuous oscillation σ ν ∝ τ − 3 / 2 − σ ν ∝ τ 1 / 2 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 5 P 1 / 2 D1 line ： 794.7 nm 5 S 1 / 2 1 1 = − = + m m s s 2 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 = ± P 69 . 4 1 . 9 % Non-coating ： T W ≈ 3 min. @ Xe 100 torr Coated cell ： T W ≈ 20 min.
Spin maser Transverse magnetic field - synchronism with spin precession - Phase : perpendicular to the transverse polarization Amplitude : proportional to the transverse polarization Relaxation, Polarization’s growing B 0 pumping (pumping effect) T2 relaxation Feedback torque Polarization vector : M Polarization Feedback torque Feedback field : B fb Population inversion pump Feedback system Feedback EM-field synchronism with emitted photon Zeeman level
Optical-detection-feedback NMR-based spin maser spin maser Spin maser with the tuned coil Artificial feedback through of tank circuit the optical spin detection L B 0 ∼ mG B 0 Probe laser Feedback coil B FB beam Phase shifter Induced current Lock-in detection I ∝ nPQ Photo diode C Nuclear spin 1 γ 0 = B Pumping laser beam LC Pumping light Oscillation Operation at low magnetic field 1 1 γ ηµ > 2 h Q InP threshold 0 0 Small field fluctuation 2 T 2 High-sensitive magnetometer ν > kHz (B 0 = 1 G) Long intrinsic T 2
Optical detection of 129 Xe nuclear precession Transverse-polarization transfer : Rb atom Xe nuclei (re-polarization) [ ] ( ) dP ( ) Rb = γ − − Γ = γ − − Γ Rb ' Xe P P P P P P Xe Rb sd Rb se Xe Rb sd Rb Xe dt γ ’[Xe] = 7 × 10 3 /s, Γ sd = 0.2 /s Time constant of spin transfer: 10 -4 s P Rb Precession frequency of < kHz 0.3 ms Probe laser beam : single mode diode laser (794.7nm) (ms) 0 0.4 0.8 After half-period precession Xe Xe Xe Rb Rb Xe Xe Xe Circular polarization (modulated by PEM)
Experimental apparatus Magnetic shield (3 layers ) Solenoid coil (for static field) Permalloy Pumping LASER B 0 = 28.3 mG ( I = 3.58 mA) Size : l = 100 cm, d = 36, 42, 48 cm Shielding factor : S = 10 3 Tunable diode laser λ = 794.7 nm ( Rb D1 line ), ∆λ = 3 nm Output: 18 W Si photo diode Freq. band width: 0 – 500 kHz NEP: 8 × 10 -13 W/Hz Xe gas cell PEM Enriched 129 Xe : 230 torr Rb : ~ 1 mg Mod. Freq. 50 kHz Heater P xe ~ 10 % 18 mm T cell = 60 ~ 70 ℃ Pyrex spherical grass cell SurfaSil coated Probe LASER 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 Feedback coil Modulated signal Probe light 4 turns PEM Modul. Freq. （ 50 kHz) φ 20cm 129 Xe Larmor Freq.(33.5 Hz) Pumping light ref. Si photo-diode (50kHz) Feedback field Lock-in amp. R = 10 – 50 k Ω B FB = 1 PSD-signal γ T 2 Lock-in amp. （ 0.2 Hz) 3.6 µ G V Y ref. ( ∼ 33.3 Hz ) 1 µ G 1V V X ( T 2 =100s) φ = 0 ° φ = -90 ° Feedback signal (33.5 Hz) Operation circuit Wave generator
Around Xe cell LASER system Magnetic shield Pumping laser Feedback coil Probe laser Heater Xe cell PEM
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 ） 0.2 Signal (mV) 0.0 T 2 ≈ 350 s -0.2 0 100 200 300 400 500 600 Time (s) 0.16 Frequency: 0.00 ν = ν − ν = 0 . 23 Hz beat prec ref -0.16 100 110 120
129 Xe spin maser signal B 0 = 28.3 mG , ν ref = 33.20 Hz Feedback gain : 18 µ G/0.1mV 0.2 Signal (mV) 0.0 -0.2 0 1000 2000 3000 4000 Time (s) Steady state oscillation 0.1 0.0 Feedback system ON -0.1 3000 3010 3020 ν = ν − ν = Measured frequency : 0 . 32 Hz beat prec ref
Frequency characteristics φ (rad) Fourier spectrum ( 1 hr. run ) 10000 Precession angle Artificial feedback 0 spin maser 0 10000 5000 ( ν = 33.5 Hz ) t (sec) ν = 277.20844 ± 0.00096 mHz δν = 0.96 µ Hz σ(ν) ∝ τ -3/2 Frequency precision ( µ Hz) 100 Conventional spin maser ( ν = 3.56 kHz ) 10 1 0.1 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 Residual field Measured field z (cm) 0 -25 -15 -5 5 15 25 -20 Field (μG) -40 Bz -60 -80 -100
High-sensitive magnetometer in low frequency spin maser Fluctuation of magnetic field → Main source of frequency noise in spin maser operation δ ≈ − δν ≈ ≈ 1 pG 10 28 B d e cm 1 nHz atom = E 10 kV/cm Neutron EDM experiment….. Hg atomic magnetometer Xe EDM experiment @ Michigan Gr. ….. 3 He co-magnetometer D. Budker et al., Atomic magnetometer with Rb using magneto-optical rotation PRA 62 (2000) 043403. Linear polarized light ( F ’=0) k σ - Alkali vapor σ + g µ B Faraday rotation B m F = -1 m F = 0 m F = +1 ( F =1) 1 × 10 4 rad/G, 4 × 10 -12 G/ √ Hz (B < 0.1G)
Estimation of experimental EDM-sensitivity Conceptual setup Installation of atomic magnetometer into low frequency spin oscillator sensitivity : 10 -11 ∼ 10 -12 G/ √ Hz ⇓ δ B ∼ 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 ( δ T ∼ 0.01 ˚ C) Probe light (Magnetometer) (E=10kV/cm) ∼ − − = 29 30 d ( Xe ) 10 10 e cm
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 µ Hz. � Construction of 4 layer magnetic shield. � Installing the Rb magnetometer with magneto-optical rotation. � Aiming at d (Xe) = 10 -29 ∼ 10 -30 ecm.
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