Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session J6: Atomic Clocks and Magnetometers |
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Chair: Chris Oates, NIST Room: Garden 4 |
Wednesday, June 6, 2012 2:00PM - 2:12PM |
J6.00001: $^{87}$Sr Clock Comparisons at JILA Jason Williams, Travis Nicholson, Benjamin Bloom, Sara Campbell, Michael Martin, Matthew Swallows, Michael Bishof, Jun Ye Great advances are being realized with optical lattice clocks, where spectroscopy at optical frequencies and large ensembles of neutral atoms combine to offer extremely high frequency precision and stability. Recent results from the Strontium 87 optical atomic clock at JILA have demonstrated that strong interactions among fermions confined in a two-dimensional (2D) optical lattice suppress the collisional frequency shift and its uncertainty to the level of 10$^{-17}$ [1]. We report on the progress of a second optical lattice clock at JILA, in which fermionic $^{87}$Sr atoms are confined in a lattice potential derived from optical buildup cavities to provide strong confinement over a very large volume in one, two, and three dimensional lattices. Intercomparisons of the two clocks at JILA will be used to explore in greater detail the physics governing the transition shifts and uncertainties in our two $^{87}$Sr optical lattice systems and will provide a significant improvement of our systematic errors.\\[4pt] [1] M~D.~Swallows \textit{et al.} Science, \textbf{331}, 1043 (2011) [Preview Abstract] |
Wednesday, June 6, 2012 2:12PM - 2:24PM |
J6.00002: S-Wave Clock Shift for Fermions E.L. Hazlett, Y. Zhang, R.W. Stites, K. Gibble, K.M. O'Hara Optical lattice clocks use ultracold fermionic atoms to minimize density-dependent frequency shifts since s-wave scattering of identical fermions is forbidden. Indeed, frequency shifts are absent in a Fermi gas if a spatially homogeneous clock field interrogates the atoms. However, any spatial inhomogeneity in the clock field produces distinguishable fermions and density-dependent frequency shifts. This is directly pertinent for optical lattice clocks since inhomogeneities are naturally larger for optical frequency fields (in comparison to microwave or radio-frequency fields). We study collisional frequency shifts in a Fermi gas for which we control and characterize both the interactions and the spatial inhomogeneity of the clock field. The frequency shifts we observe exhibit novel density dependences that are different from the mean-field shifts of homogeneously excited bosons. Our description provides a physical picture of the origin of the frequency shift and indicates the experimental parameters that must be controlled to eliminate density-dependent clock shifts. [Preview Abstract] |
Wednesday, June 6, 2012 2:24PM - 2:36PM |
J6.00003: High accuracy measurement of optical atomic clock polarizability Jeff Sherman, Nathan Lemke, Nathan Hinkley, Marco Pizzocaro, Richard Fox, Andrew Ludlow, Chris Oates The differential static polarizability of ytterbium optical clock states $\alpha_{\rm clock} \equiv \alpha(^3\!P_0) - \alpha(^1\!S_0)$ is known theoretically to $\sim$10\%. We report an experimental value of this polarizability, $\alpha_{\rm clock} = 36.2612(7)$~kHz (kV/cm)$^{-2}$ at 20 parts-per-million (ppm) accuracy~[1]. Ultracold $^{171}$Yb atoms held in an optical lattice at the ac-Stark balancing ``magic'' wavelength (759~nm) are surrounded by rigidly spaced transparent conductive planar electrodes. An ultrastable laser (578~nm) is locked to the $^1\!S_0 \leftrightarrow {}^3\!P_0$ transition in an interleaved fashion for three electrode conditions: voltage applied, reversed, and grounded. These integrated error signals yield the quadratic Stark shift and a measure of stray fields. The electrode spacing is measured interferometrically \emph{in situ}. The applied electric field at the site of the atoms deviates at the few ppm level from an infinite-planar model. When last evaluated, the ytterbium optical clock frequency uncertainty was dominated by that of the blackbody Stark shift. We show how this measurement reduces this uncertainty contribution an order of magnitude to a fractional level of $3\times10^{-17}$.\\[4pt] [1] J.A.\ Sherman et al., arXiv:1112.2766 (2011). [Preview Abstract] |
Wednesday, June 6, 2012 2:36PM - 2:48PM |
J6.00004: Anomalously small BBR shift in Tl$^+$ frequency standard Z. Zuhrianda, Marianna Safronova, Mikhail Kozlov The operation of atomic clocks is generally carried out at room temperature, whereas the definition of the second refers to the clock transition in an atom at absolute zero. This implies that the clock transition frequency should be corrected in practice for the effect of finite temperature of which the leading contributor is the blackbody radiation (BBR) shift. In the present work, we have used configuration interaction + coupled-cluster method to evaluate polarizabilities of the $6s^2~^1S_0$ and $6s6p~^3P_0$ states of Tl$^+$; $\alpha_0(^1S_0)=19.5$~a.u. and $\alpha_0(^3P_0)=21.4$~a.u.. We find dynamic correction to the BBR shift to be negligible. The resulting BBR shift at $300~K$ is $\Delta \nu_{\rm BBR}=-0.0166(17)$~Hz. This result demonstrates that near cancelation of the $^1S_0$ and $^3P_0$ state polarizabilities in monovalent B$^+$, Al$^+$, In$^+$ ions of group 13 [Safronova \textit{et al.}, PRL 107, 143006 (2011)] continues for much heavier Tl$^+$, leading to anomalously small BBR shift for this system. The corresponding relative BBR shift at $300~K$ is $|\Delta \nu_{\rm BBR}/\nu_0|=1.1(1)\times10^{-17}$. This calculation demonstrates that the BBR contribution to the fractional frequency uncertainty of the Tl$^+$ frequency standard at $300~K$ is $1\times10^{-18}$. [Preview Abstract] |
Wednesday, June 6, 2012 2:48PM - 3:00PM |
J6.00005: Developing a Portable Optical Frequency Standard with Atomic Mercury Kaitlin Moore, Emily Alden, Aaron Leanhardt A two-photon excitation strategy is proposed to couple the $^{1}$S$_{0}$ and $^{3}$P$_{0}$ levels of mercury atoms with zero nuclear spin and in the presence of zero external magnetic field.~ This excitation strategy could allow for a portable optical frequency standard based on a thermal mercury vapor with a fractional frequency resolution at the $\sim $10$^{-15}$ level.~ The $^{1}$S$_{0}\to ^{3}$P$_{0}$ transition requires two photons at 531 nm, which are generated by a compact solid state laser system.~ Detection of population in the $^{3}$P$_{0}$ state can be accomplished via subsequent excitation to higher-lying excited states, e.g. $^{3}$P$_{0}\to ^{3}$S$_{1}$ can be driven with a diode laser at 405 nm.~ We also discuss a preliminary detection technique involving collisions between mercury atoms in the $^{3}$P$_{0}$ state with ground state ammonia molecules. [Preview Abstract] |
Wednesday, June 6, 2012 3:00PM - 3:12PM |
J6.00006: Referencing an Oscillator to the Rest Mass of an Atom Michael Hohensee, Shau-Yu Lan, Brian Estey, Pei-Chen Kuan, Damon English, Pauli Kehayias, Holger M\"uller Modern atomic frequency standards are referenced to transitions between two different internal electronic states of an atom, or trapped ion. The superior fractional stability demonstrated by trapped ion clocks over previous frequency standards stems from the fact that ion clocks are referenced to an optical ($\sim 10^{14}$ Hz), rather than a microwave ($\sim 10^{10}$ Hz) transition, while the underlying systematic shifts of the ion's energy levels are controlled at comparable levels in both systems. Still higher oscillation frequencies ($\sim 10^{25}$ Hz) are exhibited by the Compton-frequency ($\nu_C\equiv mc^2/h$) phase oscillations of a massive particle's wave function, but such frequencies are too fast to access directly. In this talk, we will describe the physics of how matter-wave interferometers can indirectly access these Compton-frequency oscillations, and be used to lock a real world RF oscillator to a specific subharmonic of $\nu_C$. [Preview Abstract] |
Wednesday, June 6, 2012 3:12PM - 3:24PM |
J6.00007: Progress toward a search for spin-mass couplings of the proton Julian Valdez, Jerlyn Swiatlowski, Cesar Rios, Caitlin Montcrieffe, Derek Jackson Kimball We report progress in our experiment to use a dual-isotope rubidium magnetometer to search for a long-range coupling between proton spins and the mass of the Earth. The valence electron dominates magnetic interactions and serves as a precise co-magnetometer for the nuclei in a simultaneous measurement of Rb-85 and Rb-87 spin precession frequencies, enabling accurate subtraction of magnetic perturbations. Both Rb nuclei have valence protons, but in Rb-87 the proton spin is parallel to the nuclear spin and magnetic moment while for Rb-85 the proton spin is anti-parallel to the nuclear spin and magnetic moment. Thus anomalous interactions of the proton spin produce a differential shift between the Rb spin-precession frequencies, whereas many sources of systematic error produce common-mode shifts of the spin-precession frequencies which can be controlled through auxiliary measurements. We discuss optimization of the magnetometer sensitivity, methods to control systematic effects due to light shifts, collisions, and the gyro-compass effect, and preliminary data. [Preview Abstract] |
Wednesday, June 6, 2012 3:24PM - 3:36PM |
J6.00008: Liquid-state nuclear spin comagnetometers Micah Ledbetter, Szymon Pustelny, Dmitry Budker, Michael Romalis, John Blanchard, Alexander Pines We discuss liquid-state nuclear spin comagnetometers based on mixtures of mutually miscible solvents, each rich in a different nuclear spin. In one version thereof, thermally polarized ${\rm ^1H}$ and ${\rm ^{19}F}$ nuclear spins in a mixture of pentane and hexafluorobenzene are monitored in 1 mG fields using alkali-vapor magnetometers. In a second version, ${\rm ^1H}$ and ${\rm ^{129}Xe}$ spins in a mixture of pentane and hyperpolarized liquid xenon are monitored with a superconducting quantum interference device. In the former case, we show that magnetic field fluctuations can be suppressed by a factor of about 3400 and that frequency resolution of about ${\rm 5\times 10^{-11}~Hz}$ may be realized in roughly one day of integration. We discuss the application of liquid-state nuclear spin comagnetometers to precision measurements such as a search for spin-gravity coupling or a permanent electric dipole moment, as well as to sensitive gyroscopes. [Preview Abstract] |
Wednesday, June 6, 2012 3:36PM - 3:48PM |
J6.00009: Precision Magnetometry with Spin-Polarized Xenon Skyler Degenkolb, Aaron Leanhardt, Tim Chupp Atomic magnetometer sensitivity is a limiting factor in precision measurements, medical imaging, and industrial applications. In particular, searches for permanent electric dipole moments (EDMs) require sensitive magnetometers which interact minimally with the primary samples. Techniques based on spin-polarized gases have been very successful in this capacity, but it remains difficult to perform correct spatial and temporal averages. Previous magnetometers (e.g. alkalis or $^{199}$Hg) also suffer from material problems at the high voltages and low temperatures common in EDM experiments. We propose as a remedy real-time optical magnetometry based on spectroscopy of two-photon transitions in spin-polarized $^{129}$Xe. Thermal, diffusive, and dielectric properties of xenon allow sensitive measurements in a wide range of electromagnetic field strengths and sample volumes, while long spin coherence times and a low neutron capture cross-section are favorable in neutron EDM experiments. We report on preliminary work validating the technique in $^{171}$Yb and a parallel effort measuring the $^{129}$Xe EDM, and discuss applications to contemporary neutron EDM measurements. [Preview Abstract] |
Wednesday, June 6, 2012 3:48PM - 4:00PM |
J6.00010: Precision magnetometry using NV centers in diamond David Le Sage, Linh My Pham, Nir Bar-Gill, Chinmay Belthangady, Keigo Arai, Ronald Walsworth The nitrogen-vacancy (NV) color center in diamond promises to be an extremely useful tool for precise optical magnetometry. Individual NV centers can function as atomic-scale magnetometers, for high spatial-resolution measurements, with close proximity between the field source and sensor. Improved sensitivities may be achieved by averaging the signal from many NV centers, with a resulting trade-off between sensitivity and spatial resolution. Here, we report the best magnetic field sensitivity that has thus far been achieved using a large ensemble of NV centers. These results take advantage of many recent developments, including a technique to dramatically improve the fluorescence photon collection efficiency, dynamical decoupling of the NV spins from their spin-bath environment, and improved diamond engineering to reduce magnetic impurities and increase the density of NV centers. These ongoing efforts suggest that, with additional improvements, NV magnetometers may achieve comparable sensitivities to the best magnetometers that presently exist, with the added practical benefits associated with being a robust, solid-state, room-temperature device. [Preview Abstract] |
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