Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session Z5: Quantum Information and Cavity QED |
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Chair: Peter Maunz, University of Michigan Room: Knoxville Convention Center 301E |
Saturday, May 20, 2006 9:00AM - 9:12AM |
Z5.00001: Cavity QED with atom chips and micro-resonators Benjamin Lev, Paul Barclay, Joseph Kerckhoff, Oskar Painter, Hideo Mabuchi Cavity QED provides a rich experimental setting for quantum information processing, both in the implementation of quantum logic gates and in the development of quantum networks. Moreover, studies of cavity QED will help elucidate the dynamics of continuously observed open quantum systems with quantum- limited feedback. To achieve these goals in cavity QED, a neutral atom must be tightly confined inside a high-finesse cavity with small mode volume for long periods of time. Microfabricated wires on a substrate---known as an atom chip---can create sufficiently high-curvature magnetic potentials to trap atoms in the Lamb- Dicke regime. The integration of micro-resonators, such as microdisks and photonic bandgap cavities, with atom chips forms a robust and scalable system capable of probing the strong- coupling regime of cavity QED with magnetically trapped atoms. We have recently built an atom-cavity chip utilizing a fiber taper coupled microdisk resonator. This device combines laser cooling and trapping of neutral atoms with magnetic microtraps and waveguides to deliver cold atoms to the small mode volume of the high-Q cavity. We will relate our progress toward detecting single atoms with this device. [Preview Abstract] |
Saturday, May 20, 2006 9:12AM - 9:24AM |
Z5.00002: Optical beams with embedded vortices: building blocks for atom optics and quantum information N. Chattrapiban, I. Arakelyan, S. Mitra, W. T. Hill, III Laser beams with embedded vortices, Bessel or Laguerre-Gaussian modes, provide a unique opportunity for creating elements for atom optics, entangling photons and, potentially, mediating novel quantum interconnects between photons and matter. High-order Bessel modes, for example, contain intensity voids and propagate nearly diffraction-free for tens of meters. These vortices can be exploited to produce dark channels oriented longitudinally (hollow beams) or transversely to the laser propagation direction. Such channels are ideal for generating networks or circuits to guide and manipulate cold neutral atoms, an essential requirement for realizing future applications associated with atom interferometry, atom lithography and even some neutral atom-based quantum computing architectures. Recently, we divided a thermal cloud of neutral atoms moving within a blue-detuned beam into two clouds with two different momenta by crossing two hollow beams. In this presentation, we will describe these results and discuss the prospects for extending the process to coherent ensembles of matter. [Preview Abstract] |
Saturday, May 20, 2006 9:24AM - 9:36AM |
Z5.00003: Two-Dimensional Control of Trapped Ions in a T-junction Array of Ion Traps D. Hucul*, W.K. Hensinger**, S. Olmschenk*, D. Stick*, M. Yeo*, M. Acton*, L. Deslauriers*, J. Rabchuk***, C. Monroe* One proposal for a scalable quantum computer involves shuttling trapped atomic ions between interaction zones where ions can be entangled and storage zones where ions can be sent to store quantum information [1]. We have performed a proof of principle experiment where ions were shuttled throughout an array of linear traps arranged to make a T-junction with 11 trapping zones. These experiments were guided by simulations of the electric potential in the ion trap array, where time-varying potentials are efficiently modeled with electrode ``basis'' functions that exploit the potential of each individual electrode. In order to arbitrarily control trapped ions in two- dimensions, it may be necessary to implement four key shuttling protocols that have all been experimentally demonstrated in the T-junction array [2]: linearly shuttling ions along channels and through junctions, shuttling ions around corners, and separating and recombining two ions that are in the same trapping zone. By combining these protocols, we demonstrated the controllable swapping of the positions of two ions in the same trapping zone. [1]. D. Kielpinski et al, Nature 417, 709 (2002); M. Rowe et al., Quant. Inf. Comp. 2, 257 (2002). [2]. W. K. Hensinger et al. Appl. Phys. Lett. 88, 034101; *University of Michigan,**University of Sussex,***Western Illinois University; Work supported by the DTO and the NSF ITR program. [Preview Abstract] |
Saturday, May 20, 2006 9:36AM - 9:48AM |
Z5.00004: Using prior information for continuous measurement quantum state reconstruction. Andrew Silberfarb, Greg Smitho, Ivan Deutsch, Poul Jessen Density matrices representing quantum states must be positive.~ This restriction can provide crucial information for a quantum state-tomography procedure, allowing one to reconstruct states for which there is otherwise insufficient information.~ We explain the use of semidefinite programming techniques to enforce the positivity constraint and present an example of its use in the course of quantum state reconstruction by continuous weak measurement.~ Both simulated and experimental results for the reconstruction will be discussed for a variety of states~of a spin F=3 system in cesium, measured through polarization spectroscopy. [Preview Abstract] |
Saturday, May 20, 2006 9:48AM - 10:00AM |
Z5.00005: Unitary Integration and Fiber Bundle Geometry of N-level Quantum Systems. Dmitry Uskov, Ravi Rau Geometric properties of quantum systems, such as Berry's geometric phase and later generalizations, bring out important characteristics of quantum physics. They are now central to the field of quantum computation as a possible route to fault tolerant operation. We use fiber bundle technique to describe SU(N) quantum dynamics of N-level system as a fiber bundle over a 2(N-1)-dimensional projective space and (N-1)$^{2}$-dimensional SU(N-1)$\times $U(1) fiber. This provides a hierarchical route to a higher SU(N) groups in terms of lower dimensional ones. [Preview Abstract] |
Saturday, May 20, 2006 10:00AM - 10:12AM |
Z5.00006: Decoherence-free subspaces and spontaneous emission cancellation: necessity of Dicke limit K.-P. Marzlin, R. Karasik, B.C. Sanders, K.B. Whaley Decoherence-free subspaces (DFS) of an open quantum system are states for which the coupling to the environment is canceled by destructive interference. DFS are usually studied for states involving two or more particles and are considered a prominent candidate for quantum memory and quantum information processing. Experiments with ions indicate that partial cancellation is possible, but a demonstration of significant cancellation is challenging. \\ We prove that a perfect physical DFS requires co-located particles, i.e., the Dicke limit. The assumptions made are very general and invoke a homogeneous environment with energy-conserving coupling to the particles. We indicate when a DFS outside the Dicke limit may be possible; this includes molecular and confined systems. Furthermore, we establish a connection between DFS and spontaneous emission cancelation and refine the conditions for one of the important theorems on DFS to hold. [Preview Abstract] |
Saturday, May 20, 2006 10:12AM - 10:24AM |
Z5.00007: Detectability of dissipative motion in quantum vacuum via superradiance James Hayden Brownell, Woo-Joong Kim, Michael Brown-Hayes, Roberto Onofrio We report on a feasibility study for the detection of vacuum-induced dissipative motion, also known as the dynamical Casimir effect. Casimir photons are generated using high frequency mechanical resonators currently available through FBAR technology. The corresponding weak radio-frequency signal will stimulate population-inverted alkali atoms to generate an intense superradiant pulse detectable with conventional electronics. [Preview Abstract] |
Saturday, May 20, 2006 10:24AM - 10:36AM |
Z5.00008: Analysis of photon-atom entanglement generated by AC Stark shifts in a cavity S.K.Y. Lee, C.K. Law AC Stark shifts provide a mechanism to entangle polarization states of photons and atoms. We examine a situation in which an off-resonant light with two polarizations interacts with a collection of 4-levels atoms in a cavity. As the frequency shift in each polarization is conditioned by the number of atoms at the corresponding sub-levels, any imbalance of atom numbers would lead to a rotation of Stokes parameters of light. The quantum entanglement generated in this process is analyzed by the Schmidt decomposition method. We derive the time-dependence of entanglement entropy and the effective Schmidt number for Gaussian amplitudes. In addition, we indicate how the rate of change of entanglement is controlled by the initial fluctuations of atoms and photons. [Preview Abstract] |
Saturday, May 20, 2006 10:36AM - 10:48AM |
Z5.00009: Toward Cavity QED on an atom chip Thomas Purdy, Dan Stamper-Kurn We describe the construction and operation of microfabricated atom chips containing optical cavities suitable for cavity QED. The silicon or sapphire chips support microfabricated magnetic traps and guides for ultracold atoms, as well as Fabry- Perot optical cavities with axes perpendicular to the chips' surface. In the case of the sapphire chip, the cavities are half planar with the flat mirrors deposited directly on the surface of the chip, and curved macroscopic mirrors mounted above the chip. The silicon chip has micromachined holes through which the modes of externally mounted Fabry-Perot cavities pass. The cavities have small enough mode volume and high enough finesse to be useful as atom number detectors in a variety of on-chip experiments. Also this technology may be used in a number of cavity QED based quantum optics schemes, which would benefit from controllable magnetic loading of cold atoms into optical cavities. [Preview Abstract] |
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