Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session G5: Clocks & Tests of Fundamental Symmetries |
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Chair: D. Phillips, Harvard-Smithsonian Room: TELUS Convention Centre Glen 205 |
Thursday, June 7, 2007 8:00AM - 8:12AM |
G5.00001: Optical Lattice Clock with Fermionic Strontium S. Blatt, M.M. Boyd, A.D. Ludlow, T. Zelevinsky, S.M. Foreman, T. Zanon, G.K. Campbell, J. Ye We present recent results from our optical atomic clock based on neutral $^{87}$Sr in an optical lattice. By probing the ${{^1}\mathrm{S}_0}$-${{^3}\mathrm{P}_0}$ clock transition with a sub-Hz linewidth diode laser, we recover spectra with quality factors $Q > 2\times 10^{14}$. The clock frequency was measured as $429\,228\,004\,229\,874.0 (1.1)$~Hz, with systematic uncertainty $<9\times10^{-16}$, a level of performance approaching current Cs fountains. Stability is currently limited by the Cs-fountain-calibrated hydrogen maser used as the frequency standard. The measured frequency agrees well with our previous data as well as recent measurements by the Paris and Tokyo groups. Work toward direct comparison of optical frequency standards is in progress. [Preview Abstract] |
Thursday, June 7, 2007 8:12AM - 8:24AM |
G5.00002: Progress toward an Yb Optical Lattice Clock Zeb Barber, Jason Stalnaker, Chris Oates, Leo Hollberg Optical atomic clocks based on the $^{1}$S$_{0}-^{3}$P$_{0}$ transition in neutral Sr or Yb atoms confined to optical lattices are rapidly gathering momentum. Three different labs have published frequency measurements of Sr based standards that agree to 1 part in 10$^{14}$, and several clocks based on Yb are being built around the world. We present recent progress at NIST on an Yb optical clock. This clock utilizes a moderate ($\sim $1 mT) external magnetic field to (weakly) allow the clock transition at 578 nm in an even isotope of Yb. We have observed very narrow ($\sim $4 Hz) spectroscopic lines, measured the Stark-free lattice wavelength (759.355+/-0.001 nm), and have made comparisons against other optical frequency standards. In addition, we present investigations on the effect of lattice polarization on clock frequency shifts. We also describe the development a new laser source for the clock transition. This solid state laser system uses sum frequency generation of a 1319 nm Nd:YAG and a 1030 nm fiber laser to generate the 578nm clock light. [Preview Abstract] |
Thursday, June 7, 2007 8:24AM - 8:36AM |
G5.00003: Novel scheme to stabilize compact atomic clocks Michael Hohensee, David Phillips, Ronald Walsworth Compact atomic clocks such as CPT and N-resonance clocks are typically operated in regimes for which the resonant frequency of the clock is relatively insensitive to power and frequency fluctuations of the laser. We propose a novel scheme in which the atomic medium provides both a stable clock resonance, as well as resonances with high-sensitivity to laser fluctuations which can thus be used to control these techical variations. [Preview Abstract] |
Thursday, June 7, 2007 8:36AM - 8:48AM |
G5.00004: Testing relativistic time dilation with a two-velocity ion clock in a storage ring G. Gwinner, H. Buhr, S. Reinhardt, G. Saathoff, D. Schwalm, A. Wolf, G. Huber, S. Karpuk, C. Novotny, T.W. H\"ansch, R. Holzwarth, T. Udem, M. Zimmermann We report on a new, improved test of time dilation in special relativity via the relativistic Doppler-effect. We use an optical transition with rest-frequency $\nu$ in $^7{\rm Li}^+$ ions, stored at two different speeds of $\beta_1=0.064$ and $\beta_2=0.03 $, respectively, in the TSR heavy-ion storage ring in Heidelberg. The Doppler-shifted excitation frequencies $\nu_{\rm p}$ and $\nu_{\rm a}$ for laser beams travelling parallel and antiparallel with respect to the ions are measured simultaneously using saturation spectroscopy in separate measurements at $ \beta_1$ and $\beta_2$. The resonance conditions $\nu=\gamma (1-\beta)\nu_{\rm p}$ and $\nu=\gamma (1+\beta)\nu_{\rm a}$ yield the relation $\nu_{1 \rm p} \nu_{1 \rm a} = \nu_{2 \rm p} \nu_{2 \rm a}$, if $\gamma = 1/\sqrt{1-\beta ^2}$, as predicted by SR. Deviations, e.g. caused by the existence of preferred frames, are parametrized by $\gamma = \gamma_{\rm SR} (1+\alpha \beta^2 + ...)$. We have established a preliminary new limit of $|\alpha| < 9 \times 10^{-8}$, a $25\times$ improvement over non-storage-ring techniques. We will also review the progress towards a measurement at $\beta=0.34$ at the ESR storage ring at GSI in Darmstadt, which will be key to reducing the limit on $\alpha$ even further. [Preview Abstract] |
Thursday, June 7, 2007 8:48AM - 9:00AM |
G5.00005: Nonlinear Pressure Shifts of $^{133}$Cs Hyperfine Frequencies Fei Gong, Yuan-Yu Jau, William Happer The hyperfine (microwave) magnetic-resonance frequencies of optically pumped alkali-metal atoms in buffer-gas have long been used in compact, portable frequency standards. The buffer gas is needed to slow down the diffusion of optically pumped atoms to the cell walls, and to eliminate Doppler broadening of the microwave resonances. Van der Waals molecules, consisting of an alkali-metal atom loosely bound to a buffer gas atom, can form in such vapor cells. The molecules strongly affect the spin relaxation of alkali metal atoms in Ar, Kr and Xe gases at pressures of a few Torr. The hyperfine-shift interaction, $\delta $AI$\cdot $S, the modification a nearby buffer-gas atom makes to the Fermi contact interaction between S and the nuclear spin I of the alkali atom, can contribute to the width of the microwave resonance line, and it is responsible for the pressure shifts of the hyperfine resonance frequencies that are so important for clocks. Our experiments show that Van der Waals molecules also modify the effects of the hyperfine-shift interaction $\delta $AI$\cdot $S. For Ar pressures of a few tens of Torr or less, the shift of the microwave resonance frequency of $^{133}$Cs in Ar buffer gas is not linear in the buffer gas pressure. This occurs because the contribution to the pressure shift from molecules is suppressed when $\tau \quad \delta $A I $>$ h. [Preview Abstract] |
Thursday, June 7, 2007 9:00AM - 9:12AM |
G5.00006: Precision Search for Lorentz and CPT-violating Interactions in the Electron Sector Claire Cramer, Blayne Heckel, Eric Adelberger We report recent results from an experimental search for Lorentz and CPT-violating forces coupling to spin-polarized electrons. We record the torque on a pendulum containing $10^{23}$ polarized electrons as a function of its angle with respect to large sources of spin-polarized electrons placed outside the torsion balance apparatus or with respect to a Lorentz-violating background field fixed in space. Our constraints on the background field are complementary to constraints in the proton and neutron sectors from maser and co-magnetometer experiments. Spin-spin results can be interpreted as constraints on axion-like pseudoscalar couplings, the exchange of low-mass bosons constrained only by rotational and translational invariance, and on forces mediated by the Nambu-Goldstone bosons that would arise in the context of spontaneously broken Lorentz symmetry. These Goldstone bosons, often referred to as the ``ghost condensate" because they have a negative kinetic term in the Lagrangian stabilized by higher order terms, are particularly interesting because the energy scale accessible to our experiment is the scale on which they could contribute either to Dark Energy or Dark Matter. We will present preliminary results from the first experimental search for the unique signature of the ghost condensate's interaction with Standard Model fermions. [Preview Abstract] |
Thursday, June 7, 2007 9:12AM - 9:24AM |
G5.00007: Tests of Lorentz Symmetry with Gravitationally Coupled Atoms Jay D. Tasson, V. Alan Kostelecky Violations of Lorentz symmetry provide a potential signal for new physics at the Planck scale. At presently accessible energies, these violations are described by the Standard-Model Extension (SME). In this talk I will outline the gravitationally coupled fermion sector of the SME and discuss a new sensitivity to Lorentz violation attainable in atom- interferometer experiments. [Preview Abstract] |
Thursday, June 7, 2007 9:24AM - 9:36AM |
G5.00008: Progress towards atomic magnetometry below room temperature. Alexander Sushkov, Dmitry Budker We are working towards obtaining ultra-narrow magneto-optical resonance lines with a vapor of paramagnetic atoms in a high-density buffer gas. Such ultra-narrow lines are used in a number of precision experiments and devices, such as an atomic magnetometer. Laser ablation of sub-millimeter diameter wires, as well as bulk targets, has been used to produce atomic vapor of a number of paramagnetic atoms: silver, gold, lithium, and rubidium. Vapor densities of 10$^{11}$ cm$^{-3}$ are achieved in helium buffer gas (helium density on the order of 10$^{18}$ cm$^{-3})$ at temperatures between 30 K and 295 K. Vapor lifetimes in excess of 100 ms are observed. The techniques of optical pumping and non-linear magneto-optical rotation can now be applied to these paramagnetic atoms at temperatures far lower than those needed to maintain an appreciable saturated vapor pressure necessary for vapor cell-based experiments. [Preview Abstract] |
Thursday, June 7, 2007 9:36AM - 9:48AM |
G5.00009: Progress toward improved symmetry tests with a dual noble gas maser Alex Glenday, Matthew Rosen, David Phillips, Ronald Walsworth Measurements of spin transitions in atomic systems can be sensitive to violations of Lorentz and CPT symmetry through Zeeman frequency variations as the direction or velocity of the system changes with respect to an inertial frame. We report improved performance of the ${}^{129}$Xe/${}^3$He Zeeman maser as a device for improved tests of such fundamental symmetries. Improved temperature and mechanical stability of the maser as well as signal optimization have led to an order of magnitude improvement in frequency noise and stability. Comagnetometry of the two noble gases also enables precision measurement of new forces that couple to the spin of the neutron. [Preview Abstract] |
Thursday, June 7, 2007 9:48AM - 10:00AM |
G5.00010: Rotating Co-Magnetometer for Tests of Fundamental Symmetries S.J. Smullin, T.W. Kornack, G. Vasilakis, M.V. Romalis Recent interest in tests of Lorentz and CPT symmetries have resulted in several new limits on spin coupling to a preferred direction in space. We are developing a rotating K-$^3$He co-magnetometer to improve such limits. The co-magnetometer is based on a high sensitivity K magnetometer operating in spin-exchange relaxation free regime; in this case, the K is interacting with nuclear spin-polarized $^3$He buffer gas. When properly tuned, the coupling between the two atomic species makes the system insensitive to magnetic fields and sensitive to anomalous fields that indicate the presence of new physics. The compact co-magnetometer incorporates a number of novel features, such as a ferrite magnetic shield with much lower magnetic noise level than mu-metal and in-vacuum operation of all optical elements to reduce air convection noise and improve thermal stability. Periodic rotation of the apparatus allows much faster modulation of the expected signal. In this talk, I will discuss the performance of the apparatus and present initial results. [Preview Abstract] |
Thursday, June 7, 2007 10:00AM - 10:12AM |
G5.00011: ABSTRACT HAS BEEN MOVED TO P6.00010 |
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