Optical Clocks With Trapped Ions Ekkehard Peik - PowerPoint PPT Presentation

Time and Matter 2007, Bled, 26.-31.8.2007 Optical Clocks With Trapped Ions Ekkehard Peik Physikalisch-Technische Bundesanstalt Time and Frequency Department Braunschweig, Germany

Outline • Optical Clocks: Motivation Single-Ion Optical Clock with 171 Yb + • • Search for Variations of Fundamental Constants Possible Nuclear Optical Clock with 229 Th •

Improvement in the Accuracy of Clocks ν ≅ 10 10 /s ν ≅ 10 4 /s ν ≅ 1/s from: C. Audoin, B. Guinot: The Measurement of Time

Stability of atomic frequency standards microwave optical frequency ν 0 increases by 5 orders of magnitude

Accuracy; systematic frequency shifts some shifts are prop. to the frequency: 2. order Doppler: δν ~ T ν some shifts have absolute order of magnitude and are relatively less important in the optical range: relative shift for: Yb + 688 THz Cs 9.19 GHz quadrat. Zeeman shift at 1 μ T 4.7 ×10 -12 7.6 ×10 -17 -1.7 ×10 -14 -5.8 ×10 -16 blackbody AC Stark shift at 300 K

Optical Frequency Standard Atomic „forbidden“ transition of atoms Reference in a laser-cooled sample locked to atomic resonance, Laser short-term stabilized to passive Fabry-Perot cavity „optical clockwork“, femtosecond laser Frequency-Comb provides countable radiofrequency output Generator

Reference Systems for Optical Clocks laser-cooled ensembles single trapped of neutral atoms: laser-cooled ions: Hg + , Sr + , Yb + , In + , Al + ,... Sr, Ca, Yb, ... molecules: „simple“ atoms: I 2 , CH 4 , OsO 4 ... H, He, ... nuclei: 229 Th, ...

miniature Paul trap Optical Frequency Standards with a Laser-Cooled Ion in a Paul Trap ~ Quadrupole Electrodes 5 Yb + ions • Lamb-Dicke confinement with small trap shifts • unlimited interaction time • single ion: no collisions • stability: use high-Q transition

Projection Noise Limited State Detection via Electron Shelving e t a R t Cooling n u transition o C (dipole "forbidden" n allowed) o transition t o h P Time (s) Single-ion fluorescence (In + ): Observation of a „Quantum Jump“

Yb + single-ion optical frequency standard 171 Yb + level scheme Measurement cycle 40 ms 40 - 120 ms

High resolution spectroscopy of the quadrupole transition at 688 THz Pi-Pulse „standard operation“ Close to the resolution limit τ (pulse)=1 ms τ (pulse)=30 ms τ (pulse) = 90 ms ≈ 2 ⋅τ (Yb + ) 1 kHz linewidth 30 Hz linewidth 10 Hz linewidth

Frequency comparison between two trapped 171 Yb + ions For nominally unperturbed conditions in both traps we observe a frequency difference of 0.26(42) Hz, comparable to the best relative agreement between cesium fountain clocks. 6 x 10 -16 T. Schneider, E. Peik, Chr. Tamm, Phys. Rev. Lett. 94 , 230801 (2005)

Setup for absolute optical frequency measurements + Yb trap Cs fountain ν in units of Yb+ SI Hertz 688 THz 5 MHz Laser frequency servo, (435.5 nm) time constant: 10...30 s Femtosecond Σ Reference H Maser frequency comb Clock laser cavity generator 100 MHz 344 THz (871 nm) 200 fib li k

Results of absolute frequency measurements 2000-2006 20 171 Yb + S 1/2 - D 3/2 : fYb-688 358 979 309 307.6 Hz 688 358 979 309 307.5(1.4) Hz 10 0 -10 -20 51500 52000 52500 53000 53500 54000 Day of Measurement (MJD) Main contributions to the uncertainty budget of the measurements in 2005 and 2006: u A =0.40 Hz (continuous measurements up to 36 h) u B (Cs)=0.83 Hz u B (Yb + )=1.05 Hz (quadrupole shift, blackbody AC Stark shift)

Search for Temporal Variations of Fundamental Constants

Evidence for a varying fine structure constant on a cosmological time scale ? Analysis of absorption spectra in the light from quasars, J. Webb, M. Murphy, V. Flambaum et al., Univ. New South Wales, Sydney Many Multiplet Method: transition frequencies in MgI, MgII, FeII, CrII etc. have different dependence on α because of relativistic contributions.

Result: >4 σ evidence for α -variation. Linear fit: Measurements from other groups with a different instrument, different selections of quasars and absorption lines are consistent with Δα=0 . See e.g., R. Srianand et al., Phys. Rev. Lett. 92 , 121302 (2004) E. Reinhold et al., Phys. Rev. Lett. 96 , 151101 (2006): 3.5 σ evidence for a rel. change in m e /m p of 2x10 -5 over 12 Gyr.

Search for variations of the fine structure constant S. G. Karshenboim physics/0311080 in atomic clock comparisons relativistic level shift: 2 relative frequency drift rate Yb + Ba + H Ca ∼ In + Sr + 0 Hg + -2 Yb + -4 calculations by -6 -4 -2 0 2 4 V. Dzuba and V. Flambaum sensitivity factor A heavy atoms, light atoms heavy atoms, j g > j e j g < j e

New Limits for Temporal Variations of Fundamental Constants Combining the data from Yb + with those from the Hg + frequency standard at NIST, W. H. Oskay et al., Phys. Rev. Lett. 97 , 020801 (2006), yields For the fine structure constant: For the Rydberg frequency: 3 Hg + 2 d ln Ry / dt (10 -15 yr -1 ) 1 Yb + 0 -1 E. Peik et al., physics/0611088 -2 Proc. 11th Marcel Grossmann Meeting, Berlin 2006 -3 -1.0 -0.5 0.0 0.5 1.0 NIST group: d ln α / dt (10 -15 yr -1 ) T. Fortier et al., PRL 98, 070801 (2007)

Limits for changes of the fine structure constant from laboratory experiments Early work: 2.7× 10 -13 / yr 1993: Mg FS / Cs HFS + astro. data: 1995: H HFS / Hg + HFS: 3.7× 10 -14 / yr * 2003: Rb HFS / Cs HFS * 6 2004: H / Hg + 2004: H / Hg + / Yb + 4 2006: Hg + / Yb + 2007: Dy 2 2007: Hg + / Cs HFS * 0 * assuming constancy -6 -4 -2 0 2 4 of the strong interaction d ln α / dt (10 -15 per year)

A Nuclear Optical Clock? Th-229:

The Thorium Isomer at 7.6 eV: An Optical Mössbauer Transition The lowest-lying known excited state of a nucleus is an isomer of Th-229. This nucleus can be excited by the absorption of VUV light. Measurements of Δ E 229m Th Isomer _ + Δ E [eV] Year 3 Method 2 [631] γ -Spectr. <100 1976 -1 (4) 1990 “ Δ E=7.6 eV <5 1990 d-Scatt. γ -Spectr* 3.5 (1.0) 1994 M1 transition τ =10 4 s 3.4 (1.8) 2003 “ 7.6 (0.5) 2007 “ _ + 5 *R. Helmer and C. Reich, Idaho [633] 2 “ V. Barci et al., Nice 229 Th Ground State “ B. Beck et al., LLNL

Detection of the Nuclear Excitation in Nuclear-Electronic Double-Resonance with a Single Ion: Observation of Quantum Jumps Nucleus in the ground state; Laser excitation of the nucleus; laser-induced fluorescence change of hyperfine structure detected in from the shell. intensity or polarisation of fluorescence. Possibility for a single-ion frequency standard with a nuclear excitation as the reference transition. • Th 3+ has suitable level scheme for laser cooling • promises a further reduction of systematic line shifts • constitutes a precision oscillator of the strong interaction E. Peik, Chr. Tamm, Europhys. Lett. 61 , 181 (2003)

Scaling of the 229 Th transition frequency ω in terms of α and quark masses: V. Flambaum: Phys. Rev. Lett. 97 , 092502 (2006) 10 5 enhancement in sensitivity to variations results from the near perfect cancellation of two O(MeV) contributions to the nuclear level energies. Comparing the Th nuclear frequency to present atomic clocks will allow to look for temporal variations at the level 10 -20 per year. See also: X. He, Z. Ren, J. Phys. G. 34 , 1611 (2007) A. C. Hayes, J. L. Friar, nucl-th/0702048

Outlook: Optical Clocks in Space proposals to ESA in the program Cosmic Vision 2015-25 • on the ground: replacement of H-masers for deep space navigation; VLBI • in earth orbit: time and frequency transfer between laboratories; gravimetry; geodesy • in the solar system: tests of general relativity; investigation of the Pioneer anomaly Design study of the SAGAS mission with laser link to a Sr + optical clock P. Wolf et al., LNE-SYRTE, Paris

Acknowledgements Ion Traps: Funding: Chr. Tamm DFG I. Sherstov FQXi B. Stein T. Schneider Frequency Comb: B. Lipphardt H. Schnatz Cesium Fountain: S. Weyers R. Wynands Thorium: K. Zimmermann