Ultrahigh precision observation of nuclear spin precession and application to EDM measurement T. Inoue, T. Furukawa, H. Hayashi, M. Tsuchiya, T. Nanao, A. Yoshimi A, M. Uchida, and K. Asahi Department of Physics, Tokyo Institute of Technology A Nishina Center, RIKEN International Workshop on Physics of Nuclei at Japan 26. Jan. 2010

Outline ◇ Electric Dipole Moment (EDM) - EDM and T - violation - Status of EDM experiment ◇ 129 Xe “active” nuclear spin maser - Character of 129 Xe atom - Experimental apparatus - Optical pumping and optical detection - Nuclear spin maser ◇ Experimental result - Present status of spin maser ◇ On going R & D - Feedback system of solenoid current - Improvement of the optical pumping efficiency ◇ Summary and future

： T-violation CP-violation (by CPT theorem) Search for EDM Test of the SM and beyond SM (no SM background) (no SM background) Non-zero EDM associated with spin is direct evidence of time reversal symmetry violation Standard Model (SM) : Predicted neutron EDM is about 10 5 smaller than the present experimental upper limits. Beyond SM : Detectable EDM EDM : sensitive to the CP-violation beyond SM Classical representation Vector (parallel to spin) Time reversal ： T → t → -t → s → -s → d TimeSpinEDM::: s d -s d Electric Dipole Moment (EDM)

Standard Model (d n = ~ ecm) Pendlebury and Hinds, NIM A 440 (00) 471 d( 129 Xe) < 4.1× ecm Rosenberry and Chupp, PRL 86 (2001) 22 d( 199 Hg) < 3.1× ecm W.C. Griffith et al., PRL 102 (2009) Neutron EDM predicted values |d n | < 2.9 × ecm C.A. Baker et al., PRL. 97 (2006) Historical Limits of EDMs

E parallel to BE anti-parallel to B Energy shift according to E direction Small shift of spin precession frequency EDM measurement => measurement of the tiny shift in the frequency of the spin precession BE s B-E s Hamiltonian: Energy level of spin1/2 system (if  > 0, d > 0) Principles of EDM measurement

Character of 129 Xe atom ● Stable particle High density ： ～ atom/cm room temperature ● High polarization and Long relaxation time Polarization : P ( 129 Xe) ~ 40 % (AFP-NMR) Relaxation time :T w ～ 20 min ● Spin maser technique AFP-NMR signal spin maser Free spin precessionSteady oscillation (maser state) Search for d( 129 Xe) using “Active” nuclear spin maser Goal : d( 129 Xe) ~ ecm  Continuous spin precession (maser oscillation) Transverse spin ☐ Accumulation of free spin precession ++ · · · · + Transverse spin

Probe laser ・ DFB laser ・ Wavelength : nm (Rb D1 line) ・  = 8.4×10 -6 nm ・ Output : 15 mW Pumping laser ・ Wavelength : nm (Rb D1 line) ・  = 3 nm ・ Output : 11 W PEM Heater Circularly polarizing plate Si photo diode ・ Band width : 0 ～ 500 kHz ・ NEP : 8  W/Hz Magnetic shield (4 layers) ・ Permalloy (Fe-Ni alloy) Solenoid colil (for static field) ・ B 0 = 30.6 mG (I 0 = mA) 129 Xe : 230 torr N 2 : 100 torr Rb : ~ 1 mg Pyrex glass SurfaSil coated 18 mm 129 Xe gas cell Experimental apparatus 129 Xe nuclear spin polarization 129 Xe Rb 129 Xe N2N2 N2N2 Rb 129 Xe Nuclear spin polrization through spin exchange interaction with Rb atom Selective excitation by circularly polarized light Rb atomic energy level Rb atomic polarization by optical pumping Optical detection of nuclear spin precession 129 Xe Rb B0B0 129 Xe Probe light ： nm circular polarization (modulated by PEM) Transmission intensity Max After half period of 129 Xe spin precession Polarization transfer from 129 Xe nuclei to Rb atom (re-pol.) 129 Xe nuclear spin precession : detected by using probe light (Rb D line) Rb 129 Xe B0B0 Transmission intensity Min Typical 129 Xe free spin precession signal

Magnetic shield (4 layers)  : 400 mm, L = 1600 mm for the outermost layer Solenoid coil  : 254 mm, L = 940 mm Heater Cell Box 129 Xe gas cell Feedback coil Heater - tube Probe laser PEM Pumping laser

Maser operation in low static field (~ mG) Small field fluctuation => Small frequency fluctuation Yoshimi et al., (2002) “Active” nuclear spin maser Production of the feedback field by using optical detection method P(t)P(t) B(t)B(t) B0B0 0 P(t)P(t) Feedback torque Relaxation, pumping effect Static magnetic field : B 0  mG Pumping light Photo diode Feedback coil Probe light Feedback circuit Lock-in detection Spin precession signal Feedback system ② Nuclear spin precession detection by optical detection method ① 129 Xe nuclear spin polarization by optical pumping method ③ Feedback signal generation by feedback system ④ Sustained Spin precession through the coupling between nuclear spin and feedback field Nuclear spin maser

Feedback system on Steady oscillation B 0 = 30.6 mG => 0 = 36.0 Hz Start-up enhancement Maser signal

Frequency precision ~ 1.5 mHz ~ 40 ppm Frequency fluctuation ~ 350 nA ~ 40 ppm Solenoid current fluctuation t > 30,000sec -> precision getting worse ⇔ drift of the solenoid current Frequency precision (present status)

○ constructing the feedback system for the solenoid current. ○ constructing the electric field application system. ○ developing the highly sensitive magnetometer. k Linear polarized light Rb atom B ○ simulating the frequency analysis. We are now ○ installing the fiber laser for the optical pumping laser. Convex lens 129 Xe gas cell

○ constructing the feedback system for the solenoid current. ○ constructing the electric field application system. ○ developing the highly sensitive magnetometer. k Linear polarized light Rb atom B ○ simulating the frequency analysis. We are now ○ installing the fiber laser for the optical pumping laser. Convex lens 129 Xe gas cell

Present situation Solenoid coil for static field ~ 1  current : ~ 7 mA voltage : ~ 10 mV Current fluctuation : ~ 500 nA/day Stability : ~ 70 ppm Stabilization of the solenoid current High precision Current monitor Stable current source1 : ~ 7 mA

www 1  Voltage reading precision : 1ppm/day Reference resistor precision : 1ppm/day www 1 k  10  100:1 resistance splitting = 140 pA/day stability mA range ±12 ppm ± 2nA/day = 14 nA/day stability Stable current source1 : ~ 7 mA Solenoid coil for static field ~ 1  Stable current source2 : ~ 1 m  KETHLEY 2002 High precision Voltage monitor, 8.5 digit ADC inc, model range ±7 ppm ± 20 nA/day = 70 nA/day stability Stabilization of the solenoid current Goal : ~ 5 ppm(~ 35 nA) Stability

Frequency precision ~ 1.5 mHz ~ 40 ppm Frequency fluctuation ~ 350 nA ~ 40 ppm Solenoid current fluctuation Improvement of Frequency precision Suppression of solenoid current drift  ~ 0.1 nHz for one week measurement   d ~ ecm (E = 10 kV/cm)

Introduction of the fiber laser for the optical pumping present pumping laser : array type high output laser <- it is difficult to irradiate the cell uniformly. introduction of the fiber laser - uniform irradiation to the cell - increase of the unit area intensity : 0.6 W/cm 2 ⇒ 0.9 W/cm 2 =>improvements of Rb polarization and 129 Xe nuclear polarization : suppression of maser amplitude fluctuation Introduction of fiber laser

Probe laser ・ DFB laser ・ Wavelength : nm (Rb D1 line) ・  = 8.4×10 -6 nm ・ Output : 15 mW PEM Heater Circularly polarizing plate Si photo diode ・ Band width : 0 ～ 500 kHz ・ NEP : 8  W/Hz Magnetic shield (4 layers) ・ Permalloy (Fe-Ni alloy) Solenoid colil (for static field) ・ B 0 = 30.6 mG (I 0 = mA) 129 Xe : 230 torr N 2 : 100 torr Rb : ~ 1 mg Pyrex glass SurfaSil coated 18 mm 129 Xe gas cell Pumping laser (Fiber laser) ・ Wavelength : nm (Rb D1 line) ・  = 3 nm ・ Output : 11 W Prism Introduction of fiber laser Fiber laser convex lens (f = 70 mm) Gran laser prism Circularly polarizing plate convex lens (f = 200 mm) PEM Convex lens 129 Xe gas cell

Spherical cell ・ good symmetry ・ scattering of pumping light <= decrease of optical pumping efficiency? Cubic cell preparation Amplitude [V] time [sec] counts Maser amplitude (steady state) Fiber laser Array laser Maser amplitude : Fiber laser v.s. Array laser ~ 4 times deterioration

Summary and Future ○ The frequency precision of 9.3 nHz (measurement time 30,000 sec) was obtained by operating the “active” spin maser. ○ The feedback system of the solenoid current is being constructed in order to suppress the current drift. ○ The fiber laser as the pumping laser was installed. However the fluctuation of the maser amplitude did not improve. The cubic cells are now being prepared. Further improvements and developments are now in progress. : ◎ Constriction of the electric field application system ◎ Development of the highly sensitive magnetometer based on NMOR; Nonlinear Magneto-Optical Rotation. ◎ Frequency analysis simulation => search for d( 129 Xe) in the level of ecm