Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session Q3: Magnetometry |
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Chair: David Phillips, Harvard-Smithsonian Center for Astrophysics Room: Gilmer Hall 190 |
Friday, May 22, 2009 8:00AM - 8:12AM |
Q3.00001: New Method for Light Shift Elimination in Optical Pumping Systems Bart McGuyer, Yuan-Yu Jau, William Happer We present a new method to eliminate the light shift in atomic frequency standards and other optical pumping systems. This method uses only frequency modulation of a radio frequency or microwave source in order to simultaneously lock the source frequency to an atomic resonance and lock the pumping light to eliminate the light shift. In contrast, conventional stabilization of both sources requires two individual modulation schemes and feedback loops, adding complexity. Our method kills two birds with one stone. The method uses fewer additional components and offers improved performance, reduced cost, and easier miniaturization than previous methods. In particular, few modifications are required for implementation in conventional vapor-cell atomic clocks. We believe this technique will be useful for atomic frequency standards and other optical pumping systems that experience the light shift. We will present experimental results validating this method in a vapor-cell clock, and will also present numerical results verifying this method. [Preview Abstract] |
Friday, May 22, 2009 8:12AM - 8:24AM |
Q3.00002: Dressed Spin of Helium-3 in the Cell at Room Temperature Ping-Han Chu, Andrea Esler, Jen-Chieh Peng, Douglas Beck, Steven Clayton, Steven E. Williamson, Jacob Yoder The dressed spin effect refers to the modification of effective magnetic moment of a particle when an oscillatory magnetic field is applied perpendicular to a constant magnetic field. A new neutron electric dipole moment (EDM) experiment plans to utilize this effect to modify the precession frequencies of polarized $^3$He and polarized ultracold neutrons stored in a superfluid helium cell. This dressed spin technique, proposed by Golub and Lamoreaux, is expected to reduce the systematic uncertainty of the EDM experiment. We have performed measurements using polarized $^3$He stored in a cell at room temperature to study the dressed spin effect. The $^3$He is polarized using the metastability spin exchange method, and the precession frequency of $^3$He was measured using pickup coils. The dressed spin effect was clearly observed for a variety of dressing field configurations. Results from this measurement will be presented and compared with theoretical calculations. Implications of this study on the neutron EDM experiment will also be discussed. [Preview Abstract] |
Friday, May 22, 2009 8:24AM - 8:36AM |
Q3.00003: Atomic Magnetometry in the AttoTesla Regime Hoan Bui Dang, Michael Romalis An atomic magnetometer operated in the spin-exchange relaxation-free (SERF) regime can have atom-shot-noise-limited fundamental sensitivity below 10 aT/$\surd $Hz. Not only does it surpass the sensitivity of superconducting quantum interference devices (SQUID's), it also proves advantageous by not requiring cryogenic refrigeration. We have designed and built a SERF magnetometer to push the current sensitivity limit. Johnson noise from mu-metal shields is avoided by using ferrite for the innermost shielding layer. The loss factor of different ferrites was measured in the selection for one with the lowest magnetization noise. With gradient measurement technique, a sensitivity level of 200 aT/$\surd $Hz was achieved at a low frequency (below 20Hz), which according to our model may be further improved by optimizing the system for a better signal-to-noise. Such a sensitive magnetometer is useful in many applications, for example thermal demagnetization measurements in rock magnetism. A particularly weakly-magnetized geological sample was measured with a very clean signal, demonstrating the practicality of the magnetometer. [Preview Abstract] |
Friday, May 22, 2009 8:36AM - 8:48AM |
Q3.00004: Spin-Damping in an RF atomic magnetometer Orang Alem, Michael V. Romalis, Karen L. Sauer Optically pumped atomic magnetometers have demonstrated an improved sensitivity over standard tuned coils for frequencies less than 50 MHz, making these radio-frequency (RF) magnetometers attractive for low-field NMR (for example, Budker and Romalis, Nature Physics 3, April 2007). Such magnetometers are often plagued by transient effects resulting in decreased sensitivity. The decay time of these transients, or ringing, can last for milliseconds, which is particularly detrimental for rapidly decaying NMR signals. We have found that actively damping the ringing of the atomic spins can significantly reduce such dead time. This spin-damping of the atomic transients is achieved through a negative feedback mechanism in which part of the optical signal during ringing is used to apply an RF field forcing the realignment of the atomic spins with the static magnetic field. We have successfully implemented spin-damping in 100 $\mu $s and recovered our femto-Tesla signal previously obscured by the ringing. [Preview Abstract] |
Friday, May 22, 2009 8:48AM - 9:00AM |
Q3.00005: Earth-Field Self Oscillating Magnetometer Eric Corsini, Brian Patton, Dmitry Budker Atomic magnetometers using ultra-narrow resonances based on coherences between Zeeman sublevels in alkali atoms, have been under development since the 1960s . Their high sensitivity makes them a possible alternative to SQUIDS without requiring the use of cryogenic equipment. While recent efforts have been dedicated to working in a magnetically shielded environment where the magnetic field can be tightly controlled, renewed interest in magnetometry in an unshielded environment leads to other challenges because of the fluctuations in the Earth magnetic field \footnote{D. Budker, M.V. Romalis, Nature Physics, \textbf{Vol. 3}, p.227-334, April 2007}. We will present experimental results on the performance of an all-optical self-oscillating atomic magnetometer/gradiometer based on alignment coherences operating at Earth magnetic field in an unshielded environment\footnote{J.M. Higbie, E Corsini and D Budker, Rev. Sci. Instrum. \textbf{77}, 113106 (2006)}. Our magnetometer combines amplitude modulated non-linear optical rotation (AM NMOR) and separate pump and probe beams. Its features are high projected sensitivity and wide bandwidth. Potential future applications range from geophysics to biomagnetic measurements in the field, and may serve as the basis of devices used in air- and space-borne platforms. [Preview Abstract] |
Friday, May 22, 2009 9:00AM - 9:12AM |
Q3.00006: Detection of scalar coupling at zero magnetic field with an atomic magnetometer Micah Ledbetter, Charles Crawford, Alex Pines, Dave Wemmer, John Kitching, Svenja Knappe, Dmitry Budker Nuclear magnetic resonance (NMR) is one of the most powerful analytical tools for elucidating molecular structure and function. Conventionally, NMR is detected using inductive pickup coils in high field environments, requiring expensive and immobile superconducting magnets. The signatures for chemical identification are chemical shift and scalar couplings between nuclei of the form $J$\textbf{I}$_{1}$\textbf{{\textbullet}I}$_{2}$, which typically lie between 1 Hz and 200 Hz. Here we demonstrate detection of both homonuclear and heteronuclear scalar couplings in a zero field environment (where the Zeeman interaction is entirely absent) using a millimeter scale microfabricated atomic magnetometer. We show that characteristic functional groups produce distinct spectra in a zero field environment and can be used for chemical identification. We obtain NMR linewidths of 0.1 Hz without using spin-echoes and measure scalar coupling parameters with a statistical uncertainty of 4 mHz. We also show that the zero field spectra of certain functional groups is remarkably simple compared to spectra obtained in low (earth) field environments. Progress towards multidimensional spectroscopy will be presented. [Preview Abstract] |
Friday, May 22, 2009 9:12AM - 9:24AM |
Q3.00007: Microfabricated spin exchange relaxation free atomic magnetometer W. Clark Griffith, Ricardo Jimenez-Martinez, Jan Preusser, Svenja Knappe, John Kitching Methods first developed at NIST for MEMS-based atomic clocks have been applied to magnetic field sensors. The sensors are built around microfabricated alkali-atom vapor cells integrated with micro-optics and a VCSEL light source. Exceptional magnetic field sensitivities can be achieved in a small volume vapor cell, especially when operated in the spin-exchange relaxation free (SERF) regime. In this technique, magnetic resonance broadening due to spin-exchange collisions is suppressed under conditions of high alkali density and low magnetic fields. We have demonstrated sensitivities better than 100 fT/Hz$^{1/2}$ with a millimeter scale SERF sensor.\footnote{V. Shah, S. Knappe, P.D.D. Schwindt, and J. Kitching, Nature Photonics, {\bf 1}, 649 (2007).} Adding flux concentrators\footnote{W.C. Griffith, R. Jimenez-Martinez, V. Shah, S. Knappe, and J. Kitching, Appl. Phys. Lett., {\bf 94}, 023502 (2009).} around the vapor cell further improves the sensitivity to 10 fT/Hz$^{1/2}$, potentially providing a low power, noncryogenic alternative to SQUID sensors. [Preview Abstract] |
Friday, May 22, 2009 9:24AM - 9:36AM |
Q3.00008: Nuclear quadrupole resonances and their effect on NMR sensors Elizabeth Donley, Tara Cubel-Liebisch, Jonathan Long, Eleanor Hodby, Ted Fisher, John Kitching Nuclear quadrupole resonances (NQR) have persistent relevance in the field of precision measurements and are generating renewed interest for applications of remote sensing -- particularly in the case of explosives detection. NQR resonances are also relevant to the application of building better rotation sensors based on nuclear magnetic resonance (NMR), since NQR interactions cause frequency shifts that complicate the realization of such sensors. In this talk, the basic concepts of NMR rotation sensing will be introduced, and an analysis of the NQR shift for $^{131}$Xe atoms (I = 3/2) will be presented in detail. In particular, a recent study of the transformation of nuclear quadrupole resonances from the pure nuclear quadrupole regime to the quadrupole-perturbed Zeeman regime will be presented [1]. This transformation presents an interesting quantum-mechanical problem, since the quantization axis changes from being aligned along the axis of the electric-field gradient tensor to being aligned along the magnetic field. \\[4pt] [1] E.A. Donley, J.L. Long, T.C. Liebisch, E.R. Hodby, T.A. Fisher, and J. Kitching, Phys. Rev. A 79, 013420 (2009). [Preview Abstract] |
Friday, May 22, 2009 9:36AM - 9:48AM |
Q3.00009: Magnetometry With High Spatial Resolution Using Cold Atoms in Dark Optical Tweezers Fredrik Fatemi, Mark Bashkansky We use Faraday spectroscopy of atoms confined to a movable crossed hollow beam trap to measure the magnetic field in a 200-micron-diameter spot over 5 mm in a single trap loading cycle. We have used blue-detuned, high-charge number hollow beams to create a box-like potential for cold Rb87 atoms. The trap and probe laser beams are scanned dynamically using acousto-optic deflection, and the magneto-optic polarization rotation of the probe is monitored by a polarimeter. The dark trap allows deep optical potentials with low photon scattering rate using near resonant ($\Delta $ = +100 GHz) light so that multiple magnetic field measurements can be made in a single loading cycle. We demonstrate the technique by mapping quadrupole magnetic fields with 10 $\mu $G field sensitivity. [Preview Abstract] |
Friday, May 22, 2009 9:48AM - 10:00AM |
Q3.00010: Magnetometric sensitivity optimization for nonlinear optical rotation with frequency-modulated light Louis Rene Jacome, Srikanth Guttikonda, Lok Fai Chan, Eric J. Bahr, Derek F. Jackson Kimball Coherence between ground-state Zeeman sublevels of alkali atoms can survive thousands of collisions with paraffin-coated cell walls. The resulting long coherence times achieved in evacuated, paraffin-coated cells enable precise measurement of energy shifts of ground-state Zeeman sublevels. In the present work, nonlinear magneto-optical rotation with frequency-modulated light (FM NMOR) is used to measure ground-state Zeeman shifts for rubidium atoms contained in a paraffin-coated cell. A systematic optimization of the magnetometric sensitivity of FM NMOR as a function of light power, detuning, frequency-modulation amplitude, and rubidium vapor density is carried out for the rubidium D1 and D2 lines. For a 5-cm diameter cell at temperature T = 25$^{o}$C, the optimal potential shot-noise-limited magnetometric sensitivity is found to be 80 pG/Hz$^{1/2}$ (corresponding to a sensitivity to Zeeman shifts of 40 $\mu $Hz/Hz$^{1/2}$ or 10$^{-19}$ eV/Hz$^{1/2})$. Application of these techniques to a new search for a long-range spin-mass coupling will be discussed. [Preview Abstract] |
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