A Search for Temporal and Gravitational Variation of  in Atomic Dysprosium Variation of Constants & Violation of Symmetries, 24 July 2010 Arman Cingöz JILA/NIST Boulder, CO Partial support by: University of California at Berkeley

Coworkers Dmitry Budker, Nathan Leefer Physics Department, University of California, Berkeley Steve Lamoreaux Yale University Alain Lapierre TRIUMF, Canada A.-T. Nguyen University of Pittsburgh Justin Torgerson Los Alamos National Laboratory Valeriy Yashchuk and Sarah Ferrell Lawrence Berkeley National Laboratory Collaborators

Outline Overview & motivation Nearly degenerate levels in dysprosium Experimental technique Variation Results/ Status Update Laser Cooling of Dy

Overview Variation of a would signify physics beyond the Standard Model and General Relativity. Violates Local Position Invariance (a component of Equivalence Principle), which states that results of non-gravitational experiments are independent of where and when they are performed WHEN: Temporal variation of fundamental constants:  V. Dzuba et. al., Phys. Rev A 68, (2003) V. Dzuba and V. V. Flambaum, Phys. Rev A 77, (2008) WHERE: Null gravitational redshift experiment: compare two different clocks side by side at the same location Recast species dependent shift in terms of gravitational variation of  V. V. Flambaum, Int. J. Mod. Phys. A22, 4937 (2007) 

Search in Atomic Dy Atomic dysprosium (Dy, Z=66) has two nearly degenerate levels that are highly sensitive to  A B   3 MHz – 1 GHz transitions in 5 isotopes  (t) d  /dt ~2.0 x Hz |  |  V. Dzuba et al, Phys. Rev A 77, (2008)  For |  /  | ~ /yr  d  /dt ~ 2 Hz/yr

Self-heterodyning Optical Comparison Opposite parity levels  can induce direct electric dipole transitions between levels  E ~ MHz  can induce transitions with an rf electric field Direct frequency counting  relaxed requirements on reference clock [  E=1 GHz requires  ~ for a mHz measurement (|  | ~ /yr )] Essentially independent of other fundamental constants A B G 

Statistical Sensitivity Transition linewidth, , is determined by the lifetime of state A (  =7.9  s)   ~20 kHz Counting rate ~ 10 9 s -1 Statistical sensitivity:  ~  /N 1/2 ~ 0.6 Hz s 1/2 T 1/2 After 1 hour of integration time,  ~10 mHz which corresponds to a sensitivity of: |  | ~ 5 x yr -1 

Additional Correlations  1 +  2  insensitive to  variation   A A B B Currently we monitor: 3.1-MHz transition in 163 Dy 235-MHz transition in 162 Dy  1 -  2  variation is twice as large

Parity Nonconservation in Dy Degeneracy between levels A and B useful for enhancing mixing due to the weak interactions Detect quantum interference beat between Stark and PNC mixing  |Hw|=|2.3 ± 2.9 (stat) ± 0.7 (sys)| Hz A. T. Nguyen et al., PRA 56, 3453 (1997) Theoretical calculations are difficult since dominant configurations do not mix; effect due to configuration mixing and core polarization  Hw=70 (40) Hz V. A. Dzuba et al., PRA 50, 3812 (1994) Recently, improved calculations suggest Hw ~ 2-6 Hz V. A. Dzuba and V. V. Flambaum, PRA 81, (2010) Stay tuned for CW PNC experiment with improved statistical sensitivity

Population 833 nm 669 nm 1397 nm 3 step population scheme: Step 1 and 2: cw laser excitation Step 3: spontaneous decay with b.r. ~30%

Detection RF 4829 nm 564 nm FM modulated rf field transfers population to state A State A decays to the ground state in two steps 564-nm light is detected

First Generation Apparatus Results (-2.4 ± 2.3) x yr -1 A.Cingöz et al., PRL 98, (2007) . k  =(-8.7 ± 6.6) x S. Ferrell et al., PRA 76, (2007)

2 nd Generation Apparatus Differentially pumped chambers 1.Oven chamber 2.Gate valve 3.Interaction chamber 2 3 AC D F E G 1 B A. Dy effusive oven B. Collimator C. Laser access port D. Two-layer magnetic shield E. 4  Optical collection system F. PMT viewport G. Rf electrodes

Current Status Operational for the past two years Collisional shifts reduced to ~ 10 mHz Shifts due to rf inhomogeneities consistent with 0 at the 10 mHz level However there were unexpected problems: DC Stark shifts due to stray charge accumulation: problem mostly for 3.1 MHz transition Zeeman shifts:  /B=  g AB  o m Fmax ~2 kHz/1mG (-0.8 ± 2.1) x yr -1 . Zeeman shifts under control at the ~0.1 Hz level Stray electric fields mostly stabilized but need further investigation

Future: Residual Amplitude Modulation RAM on top of FM creates asymmetric sideband amplitudes which leads to apparent shift of zero crossing for 1 st harmonic Due to the large linewidth, RAM is a serious problem  ~450 Hz/% RAM Measured value in our system  ~1 x  4 Hz shifts Various ways to control: Choose proper phase angle Active stabilization

Laser Cooling of Dy Increase beam brightness A better control of beam density  Study self collisions  Reduce systematics due to spatial inhomogeneities A strong cycling transition exists  421 nm (  = 4.6 ns) However, many decay channels Calculations suggested B.R. of <10 -4 V. A. Dzuba and V. V. Flambaum, PRA 81, (2010)

Laser Cooling of Dy 421 nm source: 1cm PPKTP in a bow tie cavity 90 mW out with 335 mW IR, 27% c.e. Transverse cooling experiment: 3 cm interaction region: ~5000 cycles Probe velocity distribution w/ 658 nm transition 658 nm 421 nm Limit on branching ratio: < 5 x More stringent limit from MOT experiment in Urbana-Champaign: 7 x M. Lu et al., PRL 104, (2010) N. Leefer et al., PRA 81, (2010) Rec. vel. 0.6 cm/s Doppler limit 20 cm/s Doppler temp. 0.8 mK Fit to Voigt Profile: Gaussian width of 0.8(5) MHz Lorentzian width of 4.2 (7) MHz

Conclusion The nearly degenerate levels in dysprosium are highly sensitive to  variation. Direct frequency counting techniques allow for measurements without state-of-the-art atomic clocks. First generation apparatus sensitivity is ~ yr -1 Second generation apparatus sensitivity is expected to be ~ yr -1. Actual data taking will commence soon. Transverse cooling of Dy to the Doppler limit has been demonstrated for all isotopes with large abundance. XUV Frequency Combs: Monday Poster Session (Mo 89)

A.- T. Nguyen et al. PRA Phys. Rev. A 69, (2004) Systematic Effects However, it is not the size but the stability of these effects that is important  preliminary analysis showed that systematic effects may be controlled to a level corresponding to |  /  | ~ 5 x /yr.

Search in Atomic Dy

Lock-in Detection Technique rf field is frequency modulated at 10 kHz with a modulation index of 1 Reduces asymmetries in the line shape caused by drifts (laser and atomic beam fluctuations) Currently use the ratio of these two harmonics Second HarmonicFirst Harmonic

Laser Cooling of Dy

Stray B-fields If unresolved Zeeman sublevels are: sym. populated  leads to broadening, but no shifts asym. populated  leads to broadening and shifts  /B=  g AB  o m Fmax ~2 kHz/1mG Nominal config.: linearly polarized pop. beams  aligned state; no shifts Systematic due to: spatially varying stress-induced birefringence on optics.  run-to-run variations due to laser pointing variations.

 Standing Wave  Small radiative losses (closed wave guide)  Impedance matched  Transparent to light  Transparent to the atomic beam  Homogeneous electric field (no phase shifts)  Broadband: 3 MHz to 1 GHz RF Interaction Region