Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session W1: Advances in Applications of Optically-Pumped Alkalis |
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Chair: Tim Gay, University of Nebraska Room: Imperial East |
Saturday, May 29, 2010 8:00AM - 8:30AM |
W1.00001: Optically Pumped Atoms with Velocity- and Spin-Changing Collisions at Low Gas Pressures Invited Speaker: We discuss optical pumping when: (a) the collision rates of optically pumped atoms with atoms or molecules of the background gas are small enough that individual velocity groups can be preferentially excited by a monochromatic light beam, (b) the collision rates are still fast enough to partially transfer the spin polarization to other velocity groups, and (c) there are non-negligible losses of polarization due to collisional spin relaxation and Larmor precession. These conditions lead to a strong correlation between the velocity and the spin polarization of the atoms--that is, to ``spin-tagging'' of the different velocity groups. This regime is similar to that of optically pumped 23Na atoms of the earth's upper atmosphere, but it is seldom encountered in laboratory experiments. For cooling and trapping experiments, the collision rates with background gas are negligible. For gas-cell experiments the velocity-changing rates are normally so fast compared to spin relaxation or Larmor precession rates, that the atoms have a Maxwellian velocity distribution with negligible correlation between the spin-polarization and the velocity. We analyze the limiting cases of strong and weak collisions, which change the velocity by a large or small fraction, respectively, of the mean thermal velocity. The Keilson-Storer model (J. Keilson and A. E. Storer, Q. Appl. Math. 10, 243 (1952)) is used to discuss strong collisions, with memory parameter \_ = 0, and weak collisions with \_ $\rightarrow$ 1. For weak collisions, the physics can be modelled by coupled Fokker-Planck equations, identical to those for forced diffusion in a harmonic-oscillator potential well. In this limit there are solutions analogous to the quantum-mechanical coherent states of a harmonic oscillator. [Preview Abstract] |
Saturday, May 29, 2010 8:30AM - 9:00AM |
W1.00002: Rydberg-mediated quantum manipulation of atoms Invited Speaker: Rydberg-Rydberg interactions are strong enough to allow a single atom to control the evolution of a second atom several microns away [1]. Laser trapping techniques allow the atoms to be stably positioned at such distances, and optical pumping can be used to selectively prepare and/or read out the internal quantum states of the atoms. When subject to resonant Rydberg excitation, the evolution of each atom becomes conditioned on the quantum state of the other. I will describe experiments at the University of Wisconsin and elsewhere that demonstrate these and other capabilities of Rydberg-mediated quantum manipulation of atoms.\\[4pt] [1] M. Saffman, T. G. Walker, and K. Molmer, ``Quantum information with Rydberg atoms,'' arXiv:0909.4777v2 [Preview Abstract] |
Saturday, May 29, 2010 9:00AM - 9:30AM |
W1.00003: Chip-Scale Atomic Magnetometers Invited Speaker: Atomic magnetometers have reached sensitivities rivaling those of superconducting quantum interference devices (SQUIDs) in some frequency ranges [1]. A major advancement in atomic magnetometry was made possible by implementing interrogation schemes that suppress spin-exchange collisions between the alkali atoms [2]. Good signal-to-noise can be achieved by operation at very high alkali densities. At the same time, it introduces the challenge to create uniform spin-polarization and monitor the atomic precession about the magnetic field in atomic vapors with large optical densities. Off-resonant detection of the polarization rotation rather than the absorption is essential to operate in this regime. By use of microfabrication methods, we are miniaturizing such atomic magnetometers. They consist of miniature vapor cells with volumes of a few cubic millimeters integrated with micro-optical components. We present the advancement in sensitivities of such devices over nearly four orders of magnitude [3]. This allows for small low-power room-temperature devices with sensitivities that get close to those of SQUIDs in the frequency range around 100 Hz. We outline the current performance of chip-scale atomic magnetometers and the major challenges. Apart from efficient pumping and probing at high optical densities, these include magnetic noise caused by several sensor components and environmental factors, noise on the light fields, as well as magnetic fields from current-carrying parts, such as heaters, lasers, and photodetectors.\\[4pt] [1] Allred et al., Phys. Rev. Lett. 89, 130801 (2002) \\[0pt] [2] Happer and Tam, Phys. Rev. A 16, 1877 (1977) \\[0pt] [3] Griffith et al., Appl. Phys. Lett 94, 023502 (2009) [Preview Abstract] |
Saturday, May 29, 2010 9:30AM - 10:00AM |
W1.00004: Laser-polarized noble gases: a powerful probe for biology, medicine, and subatomic physics Invited Speaker: For over a decade, laser-polarized noble gases such as $^{3}$He and $^{129}$Xe have proven useful for a wide range of scientific inquiries. These include investigations of pulmonary disease using the polarized gas as a signal source for magnetic resonance imaging (MRI), measurements of various aspects of nucleon structure, and tests of fundamental symmetries. Early efforts were often limited by expensive and bulky laser systems, but ongoing advancements in solid-state lasers have enabled increasingly large volumes of polarized gas to be produced with steadily improved polarization. Equally important have been advances in the fundamental understanding of spin exchange. This has led, for example, to the introduction of hybrid mixtures of alkali metals that can increase the efficiency of spin exchange by an order of magnitude. As a consequence of these advances, the figure of merit for polarized nuclear targets has increased by roughly three orders of magnitude in comparison to early accelerator-based experiments. And in MRI applications, it has become possible to pursue increasingly sophisticated imaging protocols that provide a wide range of diagnostic information. Even the earliest noble-gas MR images of the gas space of the human lung provided unprecedented resolution. More recent work includes the use of diffusion-sensitizing pulse sequences to study lung microstructure, and tagging techniques that enable the visualization (in real-time MRI movies) of gas flow during breathing. The range of applications of laser-polarized noble gases is continuing to grow, and it is notable that with an improved understanding of the underlying physics, it is quite likely that the capabilities of this useful technology will expand for some time to come. [Preview Abstract] |
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