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The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) is a network of geographically separated, time-synchronized, optically pumped atomic magnetometers that is being used to search for correlated transient signals heralding exotic physics. The GNOME is sensitive to nuclear- and electron-spin couplings to exotic fields from astrophysical sources such as compact dark-matter objects (for example, axion stars and domain walls). Properties of the GNOME sensors such as sensitivity, bandwidth, and noise characteristics are studied in the present work, and features of the network's operation (e.g., data acquisition, format, storage, and diagnostics) are described. Characterization of the GNOME is a key prerequisite to searches for and identification of exotic physics signatures., Comment: 45 pages, 16 figures, 2 tables

Results are reported from the first full-scale search for transient signals from exotic fields of astrophysical origin using data from a newly constructed Earth-scale detector: the Global Network of Optical Magnetometers for Exotic physics searches (GNOME). Data collected by the GNOME consist of correlated measurements from optical atomic magnetometers located in laboratories all over the world. GNOME data are searched for patterns of signals propagating through the network consistent with exotic fields composed of ultralight bosons such as axion-like particles (ALPs). Analysis of data from a continuous month-long operation of the GNOME finds no statistically significant signals consistent with those expected due to encounters with topological defects (axion domain walls), placing new experimental constraints on such dark matter scenarios.

We report on measurements of atomic parity violation, made on a chain of ytterbium isotopes with mass numbers A=170, 172, 174, and 176. In the experiment, we optically excite the 6s2 1S0 -> 5d6s 3D1 transition in a region of crossed electric and magnetic fields, and observe the interference between the Stark- and weak-interaction-induced transition amplitudes, by making field reversals that change the handedness of the coordinate system. This allows us to determine the ratio of the weak-interaction-induced electric-dipole (E1) transition moment and the Stark-induced E1 moment. Our measurements, which are at the 0.5% level of accuracy for three of the four isotopes measured, allow a definitive observation of the isotopic variation of the weak-interaction effects in an atom, which is found to be consistent with the prediction of the Standard Model. In addition, our measurements provide information about an additional Z' boson., 19 pages, 4 figures, 2 tables

We present a detailed description of experimental studies of the parity violation effect in an isotopic chain of atomic ytterbium (Yb), whose results were reported in a recent paper [Antypas et al., Nat. Phys. 15, 120 (2019)]. We discuss the principle of these measurements, made on the Yb $6{s}^{2} {}^{1}{S}_{0}\ensuremath{\rightarrow}5d6s ^{3}D_{1}$ optical transition at 408 nm, describe the experimental apparatus, and give a detailed account of our studies of systematic effects in the experiment. Our results offer a direct observation of the isotopic variation in the atomic parity violation effect, a variation which is in agreement with the prediction of the standard model. These measurements are used to constrain electron-proton and electron-neutron interactions, mediated by a light ${Z}^{\ensuremath{'}}$ boson.

The Global Network of Optical Magnetometers for Exotic physics searches (GNOME) is a network of time-synchronized, geographically separated, optically pumped atomic magnetometers that is being used to search for correlated transient signals heralding exotic physics. GNOME is sensitive to exotic couplings of atomic spins to certain classes of dark matter candidates, such as axions. This work presents a data analysis procedure to search for axion dark matter in the form of topological defects: specifically, walls separating domains of discrete degenerate vacua in the axion field. An axion domain wall crossing the Earth creates a distinctive signal pattern in the network that can be distinguished from random noise. The reliability of the analysis procedure and the sensitivity of the GNOME to domain-wall crossings are studied using simulated data.

We present an experimental determination of the $4{S}_{1/2}\ensuremath{\rightarrow}6{S}_{1/2}$ transition frequency in atomic potassium $^{39}\mathrm{K}$, using direct frequency-comb spectroscopy. The output of a stabilized optical frequency comb was used to excite a thermal atomic vapor. The repetition rate of the frequency comb was scanned and the transitions were excited using stepwise two-photon excitation. The center-of-gravity frequency for the transition was found to be ${\ensuremath{\nu}}_{\mathrm{cog}}=822\phantom{\rule{0.16em}{0ex}}951\phantom{\rule{0.16em}{0ex}}698.09(13)$ MHz and the measured hyperfine $A$ coefficient of the $6{S}_{1/2}$ state was $21.93(11)$ MHz. The measurements are in agreement with previous values and represent an improvement by a factor of 700 in the uncertainty of the center-of-gravity measurement.

The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements of the absolute frequency of the Hg+ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine structure constant α to less than 2 · 10−6yr−1 and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency ratio of the Al+ and Hg+ optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10−17. The record of such measurements over the last year sensitively tests for a temporal variation of α and constrains $\dot{\alpha}/\alpha = (-1.6 \pm 2.3)\ .\ 10^{-17} {\rm yr}^{-1}$ , consistent with zero.

Time has always had a special status in physics because of its fundamental role in specifying the regularities of nature and because of the extraordinary precision with which it can be measured. This precision enables tests of fundamental physics and cosmology, as well as practical applications such as satellite navigation. Recently, a regime of operation for atomic clocks based on optical transitions has become possible, promising even higher performance. We report the frequency ratio of two optical atomic clocks with a fractional uncertainty of 5.2 × 10 –17 . The ratio of aluminum and mercury single-ion optical clock frequencies ν Al + /ν Hg + is 1.052871833148990438(55), where the uncertainty comprises a statistical measurement uncertainty of 4.3 × 10 –17 , and systematic uncertainties of 1.9 × 10 –17 and 2.3 × 10 –17 in the mercury and aluminum frequency standards, respectively. Repeated measurements during the past year yield a preliminary constraint on the temporal variation of the fine-structure constant α of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{{\alpha}}}{/}{\alpha}=(-1.6{\pm}2.3){\times}10^{-17}{/}\mathrm{year}\) \end{document} .

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over km-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1x10-16 fractional level, surpassing the best current evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts., To be published in Science, 2008

We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional uncertainty of less than 7×10-16, making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg+)=1 064 721 609 899 145.30(69) Hz.

Results of an investigation of collisional deexcitation of the metastable $6s6p{}^{3}{P}_{0}$ state in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching cross sections to be ${\ensuremath{\sigma}}_{\mathrm{He}}l13\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}{\mathrm{cm}}^{2}$ and ${\ensuremath{\sigma}}_{\mathrm{Ne}}l8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}{\mathrm{cm}}^{2}.$ The small cross sections may allow an ytterbium parity nonconservation experiment to be performed in a vapor cell. We have also measured the pressure broadening and shift of the $6s6p{}^{3}{P}_{0}\ensuremath{\rightarrow}6s7s{}^{3}{\mathrm{S}}_{1}$ and ${6s}^{2}{}^{1}{S}_{0}\ensuremath{\rightarrow}6s6p{}^{3}{P}_{1}$ transitions by helium and neon.

We have observed the Stark-induced ${6s}^{2}{}^{1}{S}_{0}\ensuremath{\rightarrow}5d6s{}^{3}{D}_{1}$ transition in Yb, and measured properties relevant to the study of atomic parity nonconservation in this transition. An atomic beam of Yb is excited by 408-nm light in the presence of an external dc electric field, resulting in cascade fluorescence at 556 nm as the excitation decays through the $6s6p{}^{3}{P}_{1}$ state. The density of the atomic beam and the fluorescence detection efficiency are calibrated by directly exciting the $6s6p{}^{3}{P}_{1}$ state with 556-nm light. Using an estimate of the ${}^{3}{D}_{1}{\ensuremath{-}}^{3}{P}_{1}$ branching fraction, we obtain a measurement of the vector transition polarizability, $|\ensuremath{\beta}|=2.18(33)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8} {\mathrm{ea}}_{0}/(\mathrm{V}/\mathrm{cm}).$ In addition, we have observed the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{\rightarrow}5d6s{}^{3}{D}_{2}$ transition at 404 nm. The electric quadrupole transition amplitude and tensor transition polarizability have been measured. We have also measured the dc Stark shifts, hyperfine structure, and isotope shifts for both transitions.

We report measurements of absolute transition frequencies and hyperfine coupling constants for the 8S_{1/2}, 9S_{1/2}, 7D_{3/2}, and 7D_{5/2} states in ^{133}Cs vapor. The stepwise excitation through either the 6P_{1/2} or 6P_{3/2} intermediate state is performed directly with broadband laser light from a stabilized femtosecond laser optical-frequency comb. The laser beam is split, counter-propagated and focused into a room-temperature Cs vapor cell. The repetition rate of the frequency comb is scanned and we detect the fluorescence on the 7P_{1/2,3/2} -> 6S_{1/2} branches of the decay of the excited states. The excitations to the different states are isolated by the introduction of narrow-bandwidth interference filters in the laser beam paths. Using a nonlinear least-squares method we find measurements of transition frequencies and hyperfine coupling constants that are in agreement with other recent measurements for the 8S state and provide improvement by two orders of magnitude over previously published results for the 9S and 7D states., 14 pages, 14 figures

We present a detailed description of the observation of parity violation in the 1S0-3D1 408-nm forbidden transition of ytterbium, a brief report of which appeared earlier. Linearly polarized 408-nm light interacts with Yb atoms in crossed E- and B-fields. The probability of the 408-nm transition contains a parity violating term, proportional to (Elight . B)[(E x Elight) . B], arising from interference between the parity violating amplitude and the Stark amplitude due to the E-field (Elight is the electric field of the light). The transition probability is detected by measuring the population of the 3P0 state, to which 65% of the atoms excited to the 3D1 state spontaneously decay. The population of the 3P0 state is determined by resonantly exciting the atoms with 649-nm light to the 6s7s 3S1 state and collecting the fluorescence resulting from its decay. Systematic corrections due to E-field and B-field imperfections are determined in auxiliary experiments. The statistical uncertainty is dominated by parasitic frequency excursions of the 408-nm excitation light due to imperfect stabilization of the optical reference with respect to the atomic resonance. The present uncertainties are 9% statistical and 8% systematic. Methods of improving the accuracy for the future experiments are discussed., Comment: 14 pages, 10 figures, submitted to PRA

Atomic parity violation has been observed in the $6{s}^{2}\text{ }^{1}S_{0}\ensuremath{\rightarrow}5d6s\text{ }^{3}D_{1}$ 408-nm forbidden transition of ytterbium. The parity-violating amplitude is found to be 2 orders of magnitude larger than in cesium, where the most precise experiments to date have been performed. This is in accordance with theoretical predictions and constitutes the largest atomic parity-violating amplitude yet observed. This also opens the way to future measurements of neutron distributions and anapole moments by comparing parity-violating amplitudes for various isotopes and hyperfine components of the transition.

Repeated measurements of the frequency ratio of 199Hg + and 27A1+ singleatom optical clocks over the course of a year yield a constraint on the possible present-era temporal variation of the fine-structure constant a. The time variation of the measured ratio corresponds to a time variation in the fine structure constant of ά/α = (-1.6 ± 2.3) × 10-17/year, consistent with no change. The frequency ratio of these clocks was measured with a fractional uncertainty of 5.2 × 10-17. Stability simulations for optical clocks whose probe period is limited by 1/f-noise in the laser local oscillator provide an estimate of the optimal probe period, as well as a modified expression for the theoretical clock stability.

We report an uncertainty evaluation of an optical lattice clock based on the $^{1}{S}_{0}\ensuremath{\leftrightarrow}^{3}{P}_{0}$ transition in the bosonic isotope $^{174}\mathrm{Yb}$ by use of magnetically induced spectroscopy. The absolute frequency of the $^{1}{S}_{0}\ensuremath{\leftrightarrow}^{3}{P}_{0}$ transition has been determined through comparisons with optical and microwave standards at NIST. The weighted mean of the evaluations is $\ensuremath{\nu}(^{174}\mathrm{Yb})=518\phantom{\rule{0.2em}{0ex}}294\phantom{\rule{0.2em}{0ex}}025\phantom{\rule{0.2em}{0ex}}309\phantom{\rule{0.2em}{0ex}}217.8(0.9)\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$. The uncertainty due to systematic effects has been reduced to less than $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$, which represents $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ in fractional frequency.

We report on the improved characterization and operation of an optical frequency standard based on nuclear-spin-polarized, ultracold neutral strontium confined in a one dimensional optical lattice. We implement a remote optical carrier phase link between JILA and NIST Boulder campus, permitting high precision evaluation of the Sr system with other optical standards. Frequency measurement against a free-space Ca standard enables determination of systematic shifts of the Sr standard at or below 1 x 10-16 fractional uncertainty. We observe a density-dependent shift of the clock transition and its dependence on excited state fraction, with a zero crossing of the shift. We perform a 50-hour-long absolute frequency measurement of the strontium transition referenced to the NIST-F1 Cs fountain standard. This yields a value for the Sr clock transition frequency with a fractional uncertainty of 8.6 x 10-16, limited by the H-maser and Cs standards used. This represents our fifth, and the most accurate, measurement of the 87Sr clock frequency.

We compare the frequencies of two single ion frequency standards: Al and Hg . Systematic fractional frequency uncertainties of both standards are below 10, and the statistical measurement uncertainty is below 5× 10. Recent ratio measurements show a reproducibility that is better than 10. Although single-ion optical frequency standards promise a potential accuracy of 10 or better, this long-standing goal has not yet been realized due to various technical difficulties. Here we report progress for the NIST Hg and Al single-ion standards, as their systematic fractional frequency uncertainty approaches 10. In these measurements, the fourth harmonics of two clock lasers are locked to the mercury and aluminum clock transitions at 282 and 267 nm respectively. An octave-spanning self-referenced Ti:Sapphire femtosecond laser frequency comb (FLFC) is phase-locked to one clock laser, and the heterodyne beat-note of the other clock laser with the nearest comb-tooth is measured. The various beat-note and offset frequencies can be combined to yield a frequency ratio, which is independent of the Cs-based definition of the second, allowing this ratio to be measured even more accurately than the fundamental unit of time can be realized. In more recent comparisons of the frequencies of the two clock lasers, an octave-spanning self-referenced fiber comb laser has provided a second independent measure of the frequency ratio.

We summarize recent developments in direct frequency-comb spectroscopy that allowed high-resolution, broad-bandwidth measurements of multiple atomic and molecular resonances using only a phase-stabilized femtosecond laser, opening the way for merging precision spectroscopy with coherent control.

We report on our recent evaluations of stability and accuracy of the JILA Sr optical lattice clock. We discuss precision tools for the lattice clock, including a stabilized clock laser with sub-Hz linewidth, fs-comb based technology allowing accurate clock comparison in both the microwave and optical domains, and clock transfer over optical fiber in an urban environment. High resolution spectroscopy (Q > 2 × 10) of lattice-confined, spin-polarized strontium atoms is used for both a high-performance optical clock and atomic structure measurement. Using a Ca optical standard for comparison, the overall systematic uncertainty of the Sr clock is reduced to < 2 × 10.

The phase coherence of an ultrastable optical frequency reference is fully maintained over actively stabilized fiber networks of lengths exceeding 30 km. For a 7-km link installed in an urban environment, the transfer instability is $6 \times 10^{-18}$ at 1-s. The excess phase noise of 0.15 rad, integrated from 8 mHz to 25 MHz, yields a total timing jitter of 0.085 fs. A 32-km link achieves similar performance. Using frequency combs at each end of the coherent-transfer fiber link, a heterodyne beat between two independent ultrastable lasers, separated by 3.5 km and 163 THz, achieves a 1-Hz linewidth., Comment: 4 pages, 4 figures

We present an experimental study of the lattice induced light shifts on the 1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The ``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394 799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz on the 518 THz clock transition. Also investigated were the hyperpolarizability shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2 two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By tuning the lattice frequency over the two-photon resonances and measuring the corresponding clock transition shifts, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the magic wavelength. In addition, we have confirmed that a circularly polarized lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10^-17., Accepted to PRL

Single-trapped-ion frequency standards based on a 282 nm transition in 199 Hg + and on a 267 nm transition in 27 Al + have been developed at NIST over the past several years. Their frequencies are measured relative to each other and to the NIST primary frequency standard, the NIST-F1 cesium fountain, by means of a self-referenced femtosecond laser frequency comb. Both ion standards have demonstrated instabilities and inaccuracies of less than 1 × 10 −16 .

This talk presents two different types of neutral atom optical clocks and emphasizes the systems' differences in potential performance and complexity. Approaches in attaining high stability, high accuracy, and transportable optical atomic clocks are discussed in detail.

We measure the optical transition frequencies of the 6s 2S1/2 rarr 8s 2S1/2, 9s 2S1/2, and 7d 2D3/2,5/2 transitions in a 133Cs vapor cell, with an uncertainty < 100 kHz using a femtosecond laser frequency comb.

We report, for the first time, laser spectroscopy of the {sup 1}S{sub 0}{yields}{sup 3}P{sub 0} clock transition in {sup 27}Al{sup +}. A single aluminum ion and a single beryllium ion are simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb repulsion. This coupling allows the beryllium ion to sympathetically cool the aluminum ion and also enables transfer of the aluminum's electronic state to the beryllium's hyperfine state, which can be measured with high fidelity. These techniques are applied to measure the clock transition frequency {nu}=1 121 015 393 207 851(6) Hz. They are also used to measure the lifetime of the metastable clock state {tau}=20.6{+-}1.4 s, the ground state {sup 1}S{sub 0} g factor g{sub S}=-0.000 792 48(14), and the excited state {sup 3}P{sub 0} g factor g{sub P}=-0.001 976 86(21), in units of the Bohr magneton.

We report tests of local position invariance (LPI) and constancy of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground-state hyperfine splitting in 133Cs. Analysis of the frequency ratio, extending over six years at NIST, is used to place a limit on the fractional variation of the two clocks of less than 5.8times10-6 per change in normalized solar gravitational potential, and a limit on fractional variation of the fine structure constant at alpha dot/alpha < 1.3x10-16 yr-1, assuming invariance of other fundamental constants. Comparison of our results with those previously reported for the absolute optical frequency measurements of coupled 171Yb+ versus other constraint 133Cs standard yields a coupled constraint of -0.04times10-15 < alpha dot/alpha < 0.46times10-15 yr-1 and -2.39times10-15 < d/dt In muCs/muB < 0.47times10-15 yr-1.

We describe a new laser system we have developed to probe the ultra-narrow 1S0 harr 3P0 clock transition at 578 nm in neutral ytterbium. The yellow light is produced by sum frequency generation in a periodically poled waveguide. With approximately 100 mW each from a fiber laser and Nd:YAG laser, we produce 10 mW of visible light. Stabilization of the laser to a resonance of a high finesse, environmentally isolated cavity has enabled resolution of spectroscopic features as narrow as 5 Hz.

A stabilized femtosecond frequency comb has ~106 stable optical modes spanning hundreds of terahertz, making it an ideal tool for high-resolution spectroscopy. The frequency comb used in these experiments was generated with an octave-spanning, femtosecond, mode-locked laser based on Ti:sapphire with a repetition rate of ~1 GHz. We demonstrate some features of frequency-comb spectroscopy using experiments involving calcium and cesium.

We apply direct frequency-comb spectroscopy, in combination with precision cw spectroscopy, to measure the ${\rm 4s4p} ^3P_1 \to {\rm 4s5s} ^3S_1$ transition frequency in cold calcium atoms. A 657 nm ultrastable cw laser was used to excite atoms on the narrow ($\gamma \sim 400$ Hz) ${\rm 4s^2} ^1S_0 \to {\rm 4s4p} ^3P_1$ clock transition, and the direct output of the frequency comb was used to excite those atoms from the ${\rm 4s4p} ^3P_1$ state to the ${\rm 4s5s} ^3S_1$ state. The resonance of this second stage was detected by observing a decrease in population of the ground state as a result of atoms being optically pumped to the metastable ${\rm 4s4p} ^3P_{0,2}$ states. The ${\rm 4s4p} ^3P_1 \to {\rm 4s5s} ^3S_1$ transition frequency is measured to be $\nu = 489 544 285 713(56)$ kHz; which is an improvement by almost four orders of magnitude over the previously measured value. In addition, we demonstrate spectroscopy on magnetically trapped atoms in the ${\rm 4s4p} ^3P_2$ state., Comment: 4 pages 5 figures

Revolutionary advances in the performance of atomic clocks results from some new ideas, precision spectroscopy of ultra-cold atoms, and maturing technologies of stable lasers. Frequency stabilized solid-state lasers are playing an increasingly important roles.

We report on two optical clocks: one uses freely expanding calcium atoms, while the other is based on lattice-confined ytterbium. We measure a fractional instability between the clocks of 4 x 10-16@ 100 s.

We have performed sub-Doppler spectroscopy on the narrow intercombination line of cold calcium atoms using the amplified output of a femtosecond laser frequency comb. Injection locking of a 657-nm diode laser with a femtosecond comb allows for two regimes of amplification, one in which many lines of the comb are amplified, and one where a single line is predominantly amplified. The output of the laser in both regimes was used to perform kilohertz-level spectroscopy. This experiment demonstrates the potential for high-resolution absolute-frequency spectroscopy over the entire spectrum of the frequency comb output using a single high-finesse optical reference cavity., 4 pages, 4 Figures

We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of

We report the technical details specific to our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. In these measurements the total fractional uncertainty is ap 10-15, limited by the statistical measurement uncertainty. In this paper we will address the techniques employed for the optical-to-microwave comparison itself, which had an estimated fractional uncertainty of ap 3 times 10-16, limited by the stability of the electronics used for the comparison

The paper describes two types of optical atomic clocks. The first is based on freely expanding calcium atoms and is optimized for experimental simplicity and high stability. The second is based on Yb atoms confined to an optical lattice that is designed to yield minimal shifts for the clock transition at 578 nm. Measurements of the effective beatnote between the clocks via a femtosecond-laser frequency comb show a fractional frequency instability of

We report on an experimental and theoretical study of the dynamic (ac) Stark effect on a forbidden transition. A general framework for parameterizing and describing off-resonant ac-Stark shifts is presented. A model is developed to calculate spectral line shapes resulting from resonant excitation of atoms in an intense standing light-wave in the presence of off-resonant ac-Stark shifts. The model is used in the analysis and interpretation of a measurement of the ac-Stark shifts of the static-electric-field-induced \mbox{${\rm 6s^2}~ ^1{\rm S}_0~\to ~{\rm 5d6s}~ ^3{\rm D}_1\:$} transition at 408 nm in atomic Yb. The results are in agreement with estimates of the ac-Stark shift of the transition under the assumption that the shift is dominated by that of the ${\rm 6s^2 \:} ^1{\rm S}_0\:$ ground state. A detailed description of the experiment and analysis is presented. A bi-product of this work is an independent determination (from the saturation behavior of the 408-nm transition) of the Stark transition polarizability, which is found to be in agreement with our earlier measurement. This work is part of the ongoing effort aimed at a precision measurement of atomic parity-violation effects in Yb., 15 pages, 11 figs

Nonlinear magneto-optical Faraday rotation (NMOR) on the potassium D1 and D2 lines was used to study Zeeman relaxation rates in an antirelaxation paraffin-coated 3-cm diameter potassium vapor cell. Intrinsic Zeeman relaxation rates of $\gamma^{NMOR}/2\pi=2.0(6) {\rm Hz}$ were observed. The relatively small hyperfine intervals in potassium lead to significant differences in NMOR in potassium compared to rubidium and cesium. Using laser optical pumping, widths and frequency shifts were also determined for transitions between ground-state hyperfine sublevels of $^{39}$K atoms contained in the same paraffin-coated cell. The intrinsic hyperfine relaxation rate of $\gamma^{hf}_{expt}/2\pi = 10.6(7) $Hz and a shift of $-9.1(2) $Hz were observed. These results show that adiabatic relaxation gives only a small contribution to the overall hyperfine relaxation in the case of potassium, and the relaxation is dominated by other mechanisms similar to those observed in previous studies with rubidium., Comment: 8pages, 10 figures

Dynamic nonlinear magneto-optical-rotation signals with frequency- and amplitude-modulated laser light have been observed and investigated with a spherical glass cell of 3-mm diameter containing Cs metal with inner walls coated with paraffin. Intrinsic Zeeman relaxation rates of $\gamma/(2\pi)\approx 20 $Hz and lower have been observed. Favorable prospects of using millimeter-scale coated cells in portable magnetometers and secondary frequency references are discussed., Comment: 7 pages, 9 figures

Noise properties of an idealized atomic magnetometer that utilizes spin squeezing induced by a continuous quantum nondemolition measurement are considered. Such a magnetometer measures spin precession of $N$ atomic spins by detecting optical rotation of far-detuned light. Fundamental noise sources include the quantum projection noise and the photon shot-noise. For measurement times much shorter than the spin-relaxation time observed in the absence of light ($\tau_{\rm rel}$) divided by $\sqrt{N}$, the optimal sensitivity of the magnetometer scales as $N^{-3/4}$, so an advantage over the usual sensitivity scaling as $N^{-1/2}$ can be achieved. However, at longer measurement times, the optimized sensitivity scales as $N^{-1/2}$, as for a usual shot-noise limited magnetometer. If strongly squeezed probe light is used, the Heisenberg uncertainty limit may, in principle, be reached for very short measurement times. However, if the measurement time exceeds $\tau_{\rm rel}/N$, the $N^{-1/2}$ scaling is again restored., Comment: Some details of calculations can be found in a companion note: physics/0407125

We report on a measurement of the highly forbidden $6s^2 ^1S_0 \to 5d6s ^3 D_1$ magnetic-dipole transition in atomic ytterbium using the Stark-interference technique. This amplitude is important in interpreting a future parity nonconservation experiment that exploits the same transition. We find $| | ~ = ~ 1.33(6)_{Stat}(20)_{\beta} \times 10^{-4} \mu_0$, where the larger uncertainty comes from the previously measured vector transition polarizability $\beta$. The $M1$ amplitude is small and should not limit the precision of the parity nonconservation experiment.

Recent and ongoing experiments testing various fundamental discrete symmetries are discussed, including search for parity nonconservation in dysprosium and ytterbium, investigation of possibilities of searches for parity and time-reversal invariance violation in samarium, and a test of permutation properties of photons in a two-photon transition in barium.

We demonstrate coherent transfer of optical signals with radian level noise (in a 3.5 MHz bandwidth) through a series of laser systemsspanning from 657 nm to 1535 nm and several hundred meter distances.

The authors suggest that atomic experiments measuring the interference between magnetic-dipole and electric-field-induced electric-dipole transition amplitudes provide a valuable system to study magnetoelectric Jones effects., Comment: 3 pages, 2 figures

At the previous Symposium on Frequency Standards and Metrology, H. Katori proposed using IS0 ---->3pO transitions in alkaline earth like atoms to make high performance optical clocks based on large numbers of neutral atoms tightly confined in an optical lattice. 1 This proposal was based on the use of Sr atoms, as were the initial experiments.24 In 2004 Porsev et al. proposed the use of the analogous transition in Yb at 578 nm,5 and we have been developing lattice clocks based on Yb over the past four years. While there are considerable similarities between the Sr and Yb atomic systems, there are also some important differences. Most significantly, Yb has an