Nuclear spin maser with a novel masing mechanism and its application - - PowerPoint PPT Presentation

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

• A. Yoshimi

RIKEN

• K. Asahi, S. Emori, M. Tsukui,

RIKEN, Tokyo Institute of Technology

Nuclear polarization of noble gas atoms

Large polarization ・ long relaxation time

3He , 129Xe

129Xe:

Polarization P ≈ 10 - 70 % @ O(10-100) torr Relaxation: T1 ≈ 20 min.

3He:

Polarization P ≈ 20 - 40 % @ 1 - 10 atom Relaxation : T1 ≈ 40 hours. Noble gas atoms with nuclear spin I = 1/2

3He, 21Ne, Ar, Kr, Xe, Rn

J = 0 I ≠ 0

Application to fundamental physics

T-violation

MRI with polarized 3He

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 105 smaller than the present experimental upper limit Beyond the SM : Detectable EDM Detection of non-zero EDM CP-violation beyond standard model

199Hg 129Xe

cm 10 . 4 ) Xe (

27e

d

−

× <

• M. Romalis et al., PRL 86 (2001) 2505.

cm 10 3 . 6

26 n

e d

−

× <

Neutron

P.G. Harris et al., PRL 82(1999) 904.

Washington Univ.

• M. Rosenberry and T. Chupp, PRL86(2001) 22.

Diamagnetic atom

CP-violating nucleon-nucleon interaction h dE B 2 2 + =

+

µ ω h dE B 2 2 − =

−

µ ω

h dE 4 = −

− +

ω ω B E B E

Measurement of precession frequency shift

cm 10 1 . 2 ) Hg (

28 e

d

−

× <

Washington Univ., Michigan Univ. 133Cs, 205Tl, …

Electron’s EDM

Paramagnetic atom

cm 10 10

33 31 n

e d

− − −

= Standard model (SM) : cm 10 10 ) Xe (

36 34

e d

− − −

= Supersymmetric model : d(Xe) = 10-27 ∼ 10-29 ecm (naturally)

Project of atomic EDM experiment of 129Xe at RIKEN-TIT

129Xe

Rb

Large polarization of Xe nucleus

Spin exchange with optical pumped Rb atom Nuclear polarization O(10) % @ 100 torr (1018 /cc)

Continuous nuclear spin maser with low frequency

Free Induction Decay Continuous oscillation

2 / 3 −

∝τ σν

2 / 1 −

∝τ σν

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 129Xe by optical-pumping spin-exchange

Atomic polarization of Rb by optical pumping

• W. Happer, Rev. Mod. Phys. 44 (1972) 169.

2 1 − =

s

m 2 1 + =

s

m

2 / 1

P 5

2 / 1

S 5

D1 line ： 794.7 nm

Selective excitation by circular polarized light

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 102 torr Rb ∼mg

Spin relaxation： due to wall collision Non-coating： TW ≈ 3 min. Coated cell： TW ≈ 20 min.

% 9 . 1 4 . 69 ± = P @ 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 vector : M Feedback field : Bfb

B0

Feedback torque Relaxation, pumping T2 relaxation Polarization’s growing (pumping effect) Feedback torque

Polarization

Population inversion Feedback EM-field synchronism with emitted photon pump

Feedback system Zeeman level

Artificial feedback through the optical spin detection Operation at low magnetic field

Small field fluctuation High-sensitive magnetometer Long intrinsic T2

Optical-detection-feedback spin maser

B0 ∼ mG

Probe laser beam Pumping laser beam Lock-in detection

Phase shifter

Photo diode Feedback coil Nuclear spin

NMR-based spin maser Spin maser with the tuned coil

• f tank circuit

Induced current C

B0

L I ∝ nPQ

BFB

Pumping light

LC B 1

0 =

γ

Oscillation threshold

2 2

1 2 1 T InP Q > h ηµ γ

ν > kHz (B0 = 1 G)

Transverse-polarization transfer : Rb atom Xe nuclei (re-polarization)

Optical detection of 129Xe nuclear precession

Rb Xe Xe Xe Rb Xe Xe Xe

Rb Xe

( )

Rb sd Rb Xe se Rb

P P P dt dP Γ − − = γ

[ ]( )

Rb sd Rb Xe

Xe ' P P P Γ − − = γ

γ’[Xe] = 7 × 103 /s, Γsd = 0.2 /s

0.3 ms

PRb

(ms) 0 0.4 0.8

Time constant of spin transfer: 10-4 s Precession frequency of < kHz

Probe laser beam : single mode diode laser (794.7nm)

After half-period precession

Circular polarization (modulated by PEM)

Experimental apparatus

Enriched 129Xe : 230 torr Rb : ~ 1 mg Pxe ~ 10 % 18 mm Xe gas cell Pyrex spherical grass cell SurfaSil coated

Magnetic shield (3 layers ) Permalloy Size : l = 100 cm, d = 36, 42, 48 cm Shielding factor : S = 103 Pumping LASER Tunable diode laser λ = 794.7 nm ( Rb D1 line ), ∆λ = 3 nm Output: 18 W Probe LASER Tunable diode laser with external cavity λ = 794.7 nm ( Rb D1 line ), ∆λ = 10-6 nm Output: 15 mW Solenoid coil (for static field) B0 = 28.3 mG ( I = 3.58 mA) PEM

• Mod. Freq. 50 kHz

Si photo diode

• Freq. band width: 0 – 500 kHz

NEP: 8×10-13 W/Hz Heater Tcell = 60 ~ 70 ℃

Feedback system

Producing the feedback field delayed by 90° in phase to precession signal Low pass filtering ( fcut ~ 0.8 Hz ) Reconfiguration of precession–correlated signal High S/N feedback signal

Lock-in amp. Lock-in amp. Operation circuit Wave generator Modulated signal PEM Modul. Freq.（50 kHz)

129Xe Larmor Freq.(33.5 Hz)

Probe light

4 turns φ 20cm

φ = 0° φ = -90° Si photo-diode R = 10 – 50 kΩ

VX VY

PSD-signal （0.2 Hz) Feedback signal (33.5 Hz) Feedback field

BFB = 1 γT2

Feedback coil 1 µG ( T2=100s) 1V 3.6 µG Pumping light

• ref. ( ∼ 33.3 Hz )

ref. (50kHz)

Around Xe cell LASER system

Magnetic shield Probe laser Pumping laser Feedback coil Heater Xe cell PEM

129Xe free precession signal Static magnetic field： B0 = 28.3 mG (ν(Xe)=33.5 Hz) 90°RF pulse（ 33.5 Hz , ∆t = 3.0 ms, B1 = 70 mG ) Transverse relaxation： T2 = 350 s ； （ collision with Rb atoms 、field inhomogeneity ）

0 100 200 300 400 500 600 Time (s) 0.0 0.2

• 0.2

100 110 120

Signal (mV)

0.16

• 0.16

0.00

Frequency:

Hz 23 .

ref prec beat

= − = ν ν ν

T2 ≈ 350 s

129Xe spin maser signal

0 1000 2000 3000 4000 B0 = 28.3 mG , νref = 33.20 Hz Feedback gain: 18 µG/0.1mV Feedback system ON

Steady state oscillation

0.0 0.2

• 0.2

3000 3010 3020 0.1 0.0

• 0.1

Signal (mV)

Time (s) Measured frequency:

Hz 32 .

ref prec beat

= − = ν ν ν

10 100 1000

σ(ν) ∝ τ -3/2

Frequency precision (µHz)

Time (s)

Frequency characteristics

Fourier spectrum ( 1 hr. run )

Conventional spin maser ( ν = 3.56 kHz ) Artificial feedback spin maser ( ν = 33.5 Hz ) t (sec) φ (rad) 10000 10000 5000

ν = 277.20844 ± 0.00096 mHz

δν = 0.96 µHz 1 10 100 0.1

Precession angle

In-progress improvements; magnetic shield

Construction of 4-layer shield l = 1600 mm, R= φ 400 mm Transverse: S ≈106 Longitudinal: S ≈104 Estimated shielding factor

Measured field

• 100
• 80
• 60
• 40
• 20
• 25
• 15
• 5

5 15 25 z (cm) Field (μG) Bz

Residual field

High-sensitive magnetometer in low frequency spin maser

Fluctuation of magnetic field → Main source of frequency noise in spin maser operation

cm 10 28

atom

e d

−

≈ pG 1 ≈ B δ nHz 1 ≈ δν kV/cm 10 = E

Neutron EDM experiment….. Hg atomic magnetometer Xe EDM experiment @ Michigan Gr. ….. 3He co-magnetometer

• D. Budker et al.,

PRA 62 (2000) 043403.

Atomic magnetometer with Rb using magneto-optical rotation

mF = -1 mF = 0 mF = +1 gµB σ+ σ - (F’=0) (F=1) k Linear polarized light Alkali vapor Faraday rotation B 1×104 rad/G, 4×10-12 G/√Hz (B < 0.1G)

cm 10 10 ) Xe (

30 29

e d

− −

= Installation of atomic magnetometer into low frequency spin oscillator 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 (109/cc) P(Rb) ∼ 0.01 % ( re-polarization from Xe ) ⇓ ∆ν(Xe) ∼ 0.2 nHz (δT ∼ 0.01˚C)

Estimation of experimental EDM-sensitivity

∼ Conceptual setup

Probe light (Magnetometer)

(E=10kV/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 µHz. Construction of 4 layer magnetic shield. Installing the Rb magnetometer with magneto-optical rotation. Aiming at d(Xe) = 10-29 ∼ 10-30 ecm.