1. 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

2. 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

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

4. 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, 022506 (2003) V. Dzuba and V. V. Flambaum, Phys. Rev A 77, 012515 (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) 

5. 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 10 15 Hz |  |  V. Dzuba et al, Phys. Rev A 77, 012515 (2008)  For |  /  | ~ 10 -15 /yr  d  /dt ~ 2 Hz/yr

6. Self-heterodyning Optical Comparison Opposite parity levels  can induce direct electric dipole transitions between levels  E ~ 3-1000 MHz  can induce transitions with an rf electric field Direct frequency counting  relaxed requirements on reference clock [  E=1 GHz requires  ~10 -12 for a mHz measurement (|  | ~ 10 -18 /yr )] Essentially independent of other fundamental constants 1 2 1 - 2 A B G 

7. 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 10 -18 yr -1 

8. 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

9. 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, 052515 (2010) Stay tuned for CW PNC experiment with improved statistical sensitivity

10. 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%

11. 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

12. First Generation Apparatus Results (-2.4 ± 2.3) x 10 -15 yr -1 A.Cingöz et al., PRL 98, 040801 (2007) . k  =(-8.7 ± 6.6) x 10 -6 S. Ferrell et al., PRA 76, 062104 (2007)

13. 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

14. 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 10 -15 yr -1 . Zeeman shifts under control at the ~0.1 Hz level Stray electric fields mostly stabilized but need further investigation

15. 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 10 -4  4 Hz shifts Various ways to control: Choose proper phase angle Active stabilization

16. 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, 052515 (2010)

17. 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 10 -4 More stringent limit from MOT experiment in Urbana-Champaign: 7 x 10 -6 M. Lu et al., PRL 104, 063001 (2010) N. Leefer et al., PRA 81, 043427 (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

18. 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 ~10 -15 yr -1 Second generation apparatus sensitivity is expected to be ~10 -17 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)

21. A.- T. Nguyen et al. PRA Phys. Rev. A 69, 022105 (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 10 -18 /yr.

22. Search in Atomic Dy

23. 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

24. Laser Cooling of Dy

25. 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.

26.  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