Southwest Quantum Information and Technology

Thirteenth Annual Meeting, February 17-20, 2011
Boulder, Colorado

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SESSION 7: Atoms in Cavities and Confined Modes
Session Chair:
8:30am-9:15am	Arno Rauschenbeutel, Institute of Atomic and Subatomic Physics, Vienna University of Technology
	Trapping and Interfacing Cold Neutral Atoms Using Optical Nanofibers
	Abstract. We recently demonstrated that laser-cooled cesium atoms can be simultaneously trapped and optically interfaced with a multi-color evanescent field surrounding an optical nanofiber. The atoms are localized in a one-dimensional optical lattice about 200 nm above the nanofiber surface and can be efficiently interrogated with a resonant light field sent through the nanofiber. This technique opens the route towards the direct integration of laser-cooled atomic ensembles within fiber networks, an important prerequisite for large scale quantum communication schemes. Moreover, it is ideally suited to the realization of hybrid quantum systems that combine atoms with, e.g., solid state quantum devices. Finally, the use of nanofibers for atom trapping allows one to straightforwardly realize interesting trapping geometries which are not easily accessible w! ith freely propagating laser beams.
9:15am-9:45am	Luis Orozco, Joint Quantum Institute, Dept. Physics and National Institute of Standards and Technology, University of Maryland
	Light shifts of ground-state quantum beats: A consequence of quantum jumps.
	Abstract. Spontaneous emission in resonance fluorescence is a fundamental process in which an atom loses energy and the dipole emission of radiation is interrupted, with the consequence of damping. This process has been studied under different conditions, and the analysis with two-level atoms has given many insights into the behavior of more complicated atomic structure. The multi-level atom often has ground-state hyperfine and Zeeman structure. This structure allows the manipulation of ultra-cold atoms in areas as different as atomic clocks and quantum information processing. We present a study of ground-state light shifts with weak coherent excitation when the light is quasi-resonant with an electronic excited state of⁸⁵Rb (within a linewidth). This mechanism is only discernible through the polarization mode selection (drive V, measure H) available in cavity QED and the powerful signals coming from ground-state quantum beats, and correlation measurements on the H mode. The shift requires the presence of spontaneous emission, which generally preserves the ground-state coherence but induces a significant frequency shift with the presence of even a single photon. Quantum trajectories show that quantum jumps on the driven V mode (pi transitions) that happen in between H detections cause phase shifts on the Larmor precesion. Quantum jumps interrupt the atomic dipole and transfer the differential phase accumulated by the excited state to the ground state. The stochastic process of the quantum jumps produces both a frequency shift, if the phase jumps are small compared to p, and a broadening of the spectral linewidth from the phase diffusion process. Work performed by David G. Morris, Adres D. Cimmarusti, Luis A. Orozco, Pablo Barberis-Blostein and H. J Carmichael with support from NSF, USA; CONACYT, Mexico; and The Marsden Fund of the Royal Society of New Zealand.
9:45am-10:15am	Clement Lacroute, California Institute of Technology
	Atom trapping in the evanescent field of a tapered optical fiber: towards cQED with micro-toroids and trapped atoms.
	Abstract. Authors: C. Lacroute, D. J. Alton, K. S. Choi, A. Goban, N. P. Stern, H. J. Kimble *Norman Bridge Laboratory of Physics MC 12-33, California Institute of Technology, Pasadena, California 91125, USA It has recently been shown that a two-color Far Off-Resonance optical Trap (FORT) could be generated in the evanescent field of a sub-wavelength diameter optical fiber [1]. About 2000 Cs atoms were trapped 200nm away from the fiber surface, with a 50ms lifetime. This is an important result in the context of cavity Quantum Electrodynamics (cQED) with micro-resonators, where a single atom needs to be located a few hundred nanometers away from a dielectric surface to be strongly coupled to the evanescent field of a lithographically patterned waveguide [2]. The two-color FORT consists of the combination of a red-detuned attractive potential and a blue-detuned repulsive potential [1]. The two trapping beams propagate in a sub-wavelength optical fiber, and the resulting evanescent-field potential confines the atoms radially at a distance of a few hundred nanometers from the fiber surface. Azimuthal confinement can be obtained by a right choice of relative polarizations of the trapping beams. Adding a counter-propagating red-detuned beam provides longitudinal confinement by generating a standing wave. We investigate the evanescent electric field and its polarization in the vicinity of the fiber surface, which is found to be spatially varying in all directions on the optical wavelength scale, and is not everywhere linear because of the out-of-phase, non-vanishing longitudinal component of the electric field. Elliptically polarized light can result in a splitting of the atomic Zeeman sub-levels by a so-called fictitious magnetic field [3]. We quantify this splitting for the use of a pair of "magic wavelength" trapping beams that minimize the spread in the atomic polarizabilities for both red and blue detuned light fields [4, 5], and the subsequent spread of the total trapping potential. We will discuss experimental consequences in terms of lifetime and coherence times of the trapped atoms, and the implementation of such a fiber trap in a cQED experiment using micro-toroids. This work is supported by NSF, NSSEFF, DARPA, and the Northrop Grumman Corporation. [1] Vetsch et al., PRL 104(20), pp. 203603 (2010). [2] Aoki et al., Nature 443(12), pp. 671-674 (2006). [3] I. Deutsch and P.S. Jensen, PRA 57(3), pp. 1972-1986 (1998). [4] McKeever et al., PRL 90(13), pp. 133602 (2003). [5] Kien et al., J. Phys. Soc. Jpn. 74, pp. 910-917 (2005).