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Thad Walker - One of the best experts on this subject based on the ideXlab platform.
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Spin-Exchange Pumped NMR Gyros
arXiv: Atomic Physics, 2016Co-Authors: Thad Walker, M. S. LarsenAbstract:We present the basic theory governing Spin-Exchange pumped NMR gyros. We review the basic physics of Spin-Exchange collisions and relaxation as they pertain to precision NMR. We present a simple model of operation as an NMR oscillator and use it to analyze the dynamic response and noise properties of the oscillator. We discuss the primary systematic errors (differential alkali fields, quadrupole shifts, and offset drifts) that limit the bias stability, and discuss methods to minimize them. We give with a brief overview of a practical implementation and performance of an NMR gyro built by Northrop-Grumman Corporation, and conclude with some comments about future prospects.
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Synchronous Spin-Exchange Optical Pumping.
Physical review letters, 2015Co-Authors: Anna Korver, Daniel Thrasher, Michael D. Bulatowicz, Thad WalkerAbstract:We demonstrate a new approach to precision NMR with hyperpolarized gases designed to mitigate NMR shifts due to the alkali Spin-Exchange field. The NMR bias field is implemented as a sequence of alkali (Rb) 2π pulses, allowing the Rb polarization to be optically pumped transverse to the bias field. When the Rb polarization is modulated at the noble-gas (Xe) NMR resonance, Spin-Exchange collisions buildup a precessing transverse Xe polarization. We study and mitigate novel NMR broadening effects due to the oscillating Spin-Exchange field. Spin-Exchange frequency shifts are suppressed 2500×, and Rb magnetometer gain measurements project photon shot-noise limited NMR frequency uncertainties below 10 nHz/sqrt[Hz].
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Suppression of Spin-Exchange relaxation using pulsed parametric resonance.
Physical review letters, 2013Co-Authors: Anna Korver, R. Wyllie, B. Lancor, Thad WalkerAbstract:We demonstrate that Spin-Exchange dephasing of Larmor precession at near-Earth-scale fields is effectively eliminated by dressing the alkali-metal atom Spins in a sequence of ac-coupled $2\ensuremath{\pi}$ pulses, repeated at the Larmor precession frequency. The contribution of Spin-Exchange collisions to the spectroscopic linewidth is reduced by a factor of the duty cycle of the pulses. We experimentally demonstrate resonant transverse pumping in magnetic fields as high as 0.1 G, present experimental measurements of the suppressed Spin-Exchange relaxation, and show enhanced magnetometer response relative to a light-narrowed scalar magnetometer.
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Method for deducing anisotropic Spin-Exchange rates
Physical Review A, 2010Co-Authors: Thad Walker, I. A. Nelson, S. KadlecekAbstract:Using measured Spin-transfer rates from alkali-metal atoms to $^{3}\mathrm{He}$, combined with Spin-relaxation rates of the alkali-metal atoms due to $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$, it should be possible to differentiate between isotropic and anisotropic Spin Exchange. This would give a fundamental limit on the $^{3}\mathrm{He}$ polarization attainable in Spin-Exchange optical pumping. For K-He, we find the limit to be $0.90\ifmmode\pm\else\textpm\fi{}0.11$.
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Hybrid Spin-Exchange optical pumping of 3He.
Physical review letters, 2003Co-Authors: Earl Babcock, L. W. Anderson, Ian A. Nelson, Steve Kadlecek, Bastiaan Driehuys, F. W. Hersman, Thad WalkerAbstract:We demonstrate Spin-Exchange optical pumping of 3 He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-Exchange collisions of K and 3 He atoms then transfer the angular momentum to the 3 He with much greater efficiency than Rb- 3 He. For a K-rich vapor, the efficiency of the hybrid Spin-Exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.
M V Romalis - One of the best experts on this subject based on the ideXlab platform.
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Cesium Spin-Exchange-relaxation-free magnetometer
2008Co-Authors: Igor Savukov, Dmitry Budker, Victor M Acosta, Micah P. Ledbetter, M V RomalisAbstract:We have built and tested a Cs atomic magnetometer operating in the Spin-Exchange-relaxation-free (SERF) regime at much lower temperature than a more conventional potassium SERF magnetometer developed at Princeton University.
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Spin Exchange relaxation free magnetometry with cs vapor
Physical Review A, 2008Co-Authors: M P Ledbetter, Dmitry Budker, Igor Savukov, Victor M Acosta, M V RomalisAbstract:We describe a Cs atomic magnetometer operating in the Spin-Exchange-relaxation-free (SERF) regime. With a vapor cell temperature of $103\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ we achieve intrinsic magnetic resonance widths $\ensuremath{\Delta}B=17\text{ }\ensuremath{\mu}\text{G}$ corresponding to an electron Spin-relaxation rate of $300\text{ }{\text{s}}^{\ensuremath{-}1}$ when the Spin-Exchange rate is ${\ensuremath{\Gamma}}_{\text{SE}}=14\text{ }000\text{ }{\text{s}}^{\ensuremath{-}1}$. We also observe an interesting narrowing effect due to diffusion. Signal-to-noise measurements yield a sensitivity of about $400\text{ }\text{pG}/\sqrt{\text{Hz}}$. Based on photon shot noise, we project a sensitivity of $40\text{ }\text{pG}/\sqrt{\text{Hz}}$. A theoretical optimization of the magnetometer indicates sensitivities on the order of $2\text{ }\text{pG}/\sqrt{\text{Hz}}$ should be achievable in a $1\text{ }{\text{cm}}^{3}$ volume. Because Cs has a higher saturated vapor pressure than other alkali metals, SERF magnetometers using Cs atoms are particularly attractive in applications requiring lower temperatures.
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Dynamics of two overlapping Spin ensembles interacting by Spin Exchange.
Physical review letters, 2002Co-Authors: T W Kornack, M V RomalisAbstract:We describe linear and nonlinear dynamics of Spin-polarized K and 3 He ensembles interacting by Spin Exchange. The interactions are dominated by the imaginary part of the Spin-Exchange cross section and each Spin species is primarily affected by the average magnetization of the other. Operating in a very low magnetic field we demonstrate novel dynamics when the electron and nuclear Spin precession frequencies are nearly matched. We observe transverse damping as well as a dynamic instability of the 3 He Spins interacting with polarized K vapor. We also demonstrate operation as a self-compensating comagnetometer, useful for tests of CPT violation and other precision measurements.
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high sensitivity atomic magnetometer unaffected by Spin Exchange relaxation
Physical Review Letters, 2002Co-Authors: Joel C Allred, R N Lyman, T W Kornack, M V RomalisAbstract:Alkali-metal magnetometers compete with SQUID detectors as the most sensitive magnetic field sensors. Their sensitivity is limited by relaxation due to Spin-Exchange collisions. We demonstrate a K magnetometer in which Spin-Exchange relaxation is completely eliminated by operating at high K density and low magnetic field. Direct measurements of the signal-to-noise ratio give a magnetometer sensitivity of $10\text{ }\mathrm{f}\mathrm{T}\text{ }\mathrm{H}{\mathrm{z}}^{\mathrm{\ensuremath{-}}\mathrm{1}\mathrm{/}\mathrm{2}}$, limited by magnetic noise produced by Johnson currents in the magnetic shields. We extend a previous theoretical analysis of Spin Exchange in low magnetic fields to arbitrary Spin polarizations and estimate the shot-noise limit of the magnetometer to be $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\text{ }\mathrm{T}\text{ }\mathrm{H}{\mathrm{z}}^{\mathrm{\ensuremath{-}}\mathrm{1}\mathrm{/}\mathrm{2}}$.
Andreas Voigt - One of the best experts on this subject based on the ideXlab platform.
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Quantum phase transition in the Plaquette lattice with anisotropic Spin Exchange
Journal of Magnetism and Magnetic Materials, 2004Co-Authors: Andreas VoigtAbstract:Abstract I study the influence of anisotropic Spin Exchange on a quantum phase transition in the Plaquette lattice driven by the purely quantum effect of singlet formation. I study the influence of (i) a Dzyaloshinskii–Moriya Exchange and (ii) four-Spin Exchange on the transition point by evaluating Spin–Spin correlations and the Spin gap with exact diagonalization. The results point to a stabilization of the Neel-like long range order when the Dzyaloshinskii–Moriya Exchange is added, whereas the four-Spin Exchange might stabilize the singlet order as well as the Neel-like order depending on its strength.
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Quantum phase transition in the Plaquette lattice with anisotropic Spin Exchange
Journal of Magnetism and Magnetic Materials, 2004Co-Authors: Andreas VoigtAbstract:I study the influence of anisotropic Spin Exchange on a quantum phase transition in the Plaquette lattice driven by the purely quantum effect of singlet formation. I study the influence of i) a Dzyaloshinskii-Moriya Exchange and ii) four Spin Exchange on the transition point by evaluating Spin--Spin correlations and the Spin gap with exact diagonalization. The results point to a stabilization of the Neel-like long range order when the Dzyaloshinskii-Moriya Exchange is added, whereas the four-Spin Exchange might stabilize the singlet order as well as the Neel-like order depending on its strength.Comment: LaTeX article with 4 pages and 3 figures, prepared with material for the ICM 200
William Happer - One of the best experts on this subject based on the ideXlab platform.
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Spin-Exchange broadening of atomic clock resonances
Laser Physics, 2002Co-Authors: Daniel Walter, William HapperAbstract:Spin-Exchange collisions between alkali-metal atoms broaden the resonances used for conventional gas-cell atomic clocks and severely limit the possibilities for miniaturization. Because Spin-Exchange collisions conserve angular momentum, there are two novel clock resonances, the left and right end resonances, with frequencies ω ± that can be much less broadened by Spin-Exchange collisions than the conventional 0-0 resonance. The mean frequency ω = (ω + + ω―)/2 of the end resonances can be substantially less dependent on the magnetic field, and the signal-to-noise ratio can be much larger, than is the case for the conventional 0-0 resonance.
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Energy transport in high-density Spin-Exchange optical pumping cells.
Physical review letters, 2001Co-Authors: Daniel Walter, W. M. Griffith, William HapperAbstract:We present in situ measurements of temperatures inside multi-atmosphere Spin-Exchange optical pumping cells using Raman scattering from the N2 quenching gas. Under conditions usually prevailing in Spin-Exchange optical pumping experiments, we find that gas temperatures can be elevated hundreds of degrees above ambient, and that convection plays a very important role in the heat transport of the system.
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Spin-Exchange optical pumping of noble-gas nuclei
Reviews of Modern Physics, 1997Co-Authors: Thad Walker, William HapperAbstract:Spin-Exchange optical pumping of mixtures of alkali-metal vapors and noble gases can be used to efficiently polarize the nuclei of the noble-gas atoms. Liters of noble gases at standard temperature and pressure and with nuclear Spin polarizations of several tens of percent are now used in many applications. The authors describe the basic phenomena that govern the Spin-Exchange process and review the physics of angular momentum transfer and loss in optical pumping and Spin-Exchange collisions. {copyright} {ital 1997} {ital The American Physical Society}
M. S. Larsen - One of the best experts on this subject based on the ideXlab platform.
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Spin-Exchange Pumped NMR Gyros
arXiv: Atomic Physics, 2016Co-Authors: Thad Walker, M. S. LarsenAbstract:We present the basic theory governing Spin-Exchange pumped NMR gyros. We review the basic physics of Spin-Exchange collisions and relaxation as they pertain to precision NMR. We present a simple model of operation as an NMR oscillator and use it to analyze the dynamic response and noise properties of the oscillator. We discuss the primary systematic errors (differential alkali fields, quadrupole shifts, and offset drifts) that limit the bias stability, and discuss methods to minimize them. We give with a brief overview of a practical implementation and performance of an NMR gyro built by Northrop-Grumman Corporation, and conclude with some comments about future prospects.
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Spin-Exchange-Pumped NMR Gyros
Advances in Atomic Molecular and Optical Physics, 2016Co-Authors: T G Walker, M. S. LarsenAbstract:We present the basic theory governing Spin-Exchange-pumped nuclear magnetic resonance (NMR) gyros. We review the physics of Spin-Exchange collisions and relaxation as they pertain to precision NMR. We present a simple model of operation as an NMR oscillator and use it to analyze the dynamic response and noise properties of the oscillator. We discuss the primary systematic errors (differential alkali fields, quadrupole shifts, and offset drifts) that limit the bias stability, and discuss methods to minimize them. We give with a brief overview of a practical implementation and performance of an NMR gyro built by Northrop Grumman Corporation and conclude with some comments about future prospects.