a search for temporal and gravitational variation of a in atomic dysprosium

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 Californiaat Berkeley

CoworkersDmitry Budker, Nathan Leefer

Physics Department, University of California, Berkeley

Steve Lamoreaux Yale University

Alain Lapierre TRIUMF, Canada

A.-T. NguyenUniversity of Pittsburgh

Justin Torgerson Los Alamos National Laboratory

Valeriy Yashchuk and Sarah FerrellLawrence 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, 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)

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 1015 Hz ||Ÿ

V. Dzuba et al, Phys. Rev A 77, 012515 (2008)

Ÿ•For |/| ~ 10-15 /yr d/dt ~ 2 Hz/yr

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 - 2A

B

G

Ÿ

Statistical Sensitivity

• Transition linewidth, , is determined by the lifetime of

state A ( =7.9 s) ~20 kHz

• Counting rate ~ 109 s-1

• Statistical sensitivity:

~ /N1/2 ~ 0.6 Hz s1/2

T1/2

After 1 hour of integration time, ~10 mHz which correspondsto a sensitivity of:

|| ~ 5 x 10-18 yr-1 Ÿ

Additional Correlations

1 + 2 insensitive to variation

A

A

B

B

Currently we monitor:3.1-MHz transition in 163Dy235-MHz transition in 162Dy

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)| HzA. 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 polarizationHw=70 (40) HzV. A. Dzuba et al., PRA 50, 3812 (1994)

• Recently, improved calculations suggest Hw ~ 2-6 HzV. A. Dzuba and V. V. Flambaum, PRA 81, 052515 (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 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)

2nd Generation Apparatus

Differentially pumped chambers

1. Oven chamber2. Gate valve3. Interaction

chamber

2

3

A C

D

F

E

G

1

B

A. Dy effusive ovenB. CollimatorC. Laser access portD. Two-layer magnetic shieldE. 4 Optical collection

systemF. PMT viewportG. 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=gABomFmax~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

Future: Residual Amplitude Modulation

• RAM on top of FM creates asymmetric sideband amplitudes which leads to apparent shift of zero crossing for 1st 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

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)

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/sDoppler limit 20 cm/sDoppler 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 ~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)

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.

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=gABomFmax~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

RF Interaction Region