Bulletin of the American Physical Society
2005 36th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 17–21, 2005; Lincoln, Nebraska
Session L1: Quantum Control of AMO Processes |
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Chair: Carlton Caves, University of New Mexico Room: Burnham Yates Conference Center Ballroom II |
Friday, May 20, 2005 1:30PM - 2:06PM |
L1.00001: Quantum Networking of Trapped Ions Invited Speaker: Entangling large numbers of trapped ions for quantum computing applications will require networks of cold ions trapped in multi-zone microfabricated traps, coupled either through a mutual interaction with their Coulomb-coupled motion or through a common interaction with individual photons. Progress on these fronts at Michigan will be reviewed, including the deterministic entanglement of pairs of Cd ions in a single trap, the shuttling of ions through a 49-electrode 10-zone trap, the fabrication of micron-scale ion traps, and progress in the probabilistic (but scalable) entanglement of two remotely-located ions. [Preview Abstract] |
Friday, May 20, 2005 2:06PM - 2:42PM |
L1.00002: The Preferred Ensemble Fact with Applications to Quantum Feedback Control Invited Speaker: It is well known that there are infinitely many different ensembles of pure states that are equivalent to any given mixed quantum state. The preferred ensemble \textit{fallacy} [1] is that any particular ensemble should be used in the interpretation of an experiment involving a quantum system in a mixed state. Notwithstanding this, for open quantum systems obeying a master equation that has a mixed steady state, there is a preferred ensemble \textit{fact}: only some ensembles are physically realizable. By this we mean that it is only some ensembles for which \begin{enumerate} \item an observer can know at all times which pure state member of the ensemble the system is in; and \item the weight of that state in the ensemble is the proportion of time the system spends in that state. \end{enumerate} The preferred ensemble fact has applications in quantum feedback control in LQG (linear quadratic gaussian) systems [3], which has recently been implemented experimentally in a number of systems such as spin-squeezing and nanomechanical devices. Specifically, the existence of preferred ensembles determines the quantum limit to how well certain control goals can be achieved. I will illustrate these ideas with an example from quantum optics. \newline \newline [1] P. Kok and S.L. Braunstein, Phys. Rev. A \textbf{61}, 042304 (2000). \newline [2] H.M. Wiseman and J.A. Vaccaro, Phys. Rev. Lett. \textbf{87}, 240402 (2001). \newline [3] H. M. Wiseman, and A. C. Doherty, Phys. Rev. Lett. To appear (quant-ph/0408099) [Preview Abstract] |
Friday, May 20, 2005 2:42PM - 3:18PM |
L1.00003: Weak Optical Measurements and Control of Atomic Spin Ensembles Invited Speaker: Optical polarization spectroscopy is uniquely suited as a continuous, non-destructive probe of the quantum state of an atomic spin ensemble, and provides an attractive starting point for studies of quantum measurement and control. I will broadly consider what information about the spins can be accessed, and also what kinds of spin dynamics can be driven by the atom-probe interaction. I will then discuss our recent work on optical measurement/control of the spin degrees of freedom of laser cooled Cs atoms. One experiment studies the use of Faraday rotation to probe the spin-angular momentum, and in particular the significance of tensor terms in the probe light shift Hamiltonian. The tensor terms are non-linear in the spin variables, and lead to easily observable collapse and revivals of a Larmor precessing spin-coherent state. We are now exploring the use of this non-linear term in the spin Hamiltonian to drive a more complex evolution that continually maps new information about the initial state onto the measured observable. In principle the measurement record can then be used to perform quantum state tomography non-destructively and in real time. In a second experiment we use a variation of the basic polarization spectroscopy setup to implement a continuous weak measurement of the pseudospin associated with the atomic clock transition in Cs. The measurement performance is comparable to Faraday rotation measurements of spin angular momenta, and the technique can therefore in principle be used to achieve measurement-induced squeezing of the collective pseudospin along the limes explored in [J. Geremia et al., Science 304, 270 (2004)]. Squeezing of the clock pseudospin is particularly interesting because it can be applied directly to the improvement of atom interferometers and atomic clocks. [Preview Abstract] |
Friday, May 20, 2005 3:18PM - 3:54PM |
L1.00004: Quantum Control and Transport of a Bose-Einstein Condensate Invited Speaker: I will discuss recent work in my group on many-body quantum control and transport. In our rubidium experiment, a single Bose-Einstein condensate is optically trapped in crossed TEM01 modes, and we achieve confinement in two dimensions that is comparable to an optical lattice, but with single-atom addressability and detection. These conditions should enable the experimental realization of a ``quantum tweezer'' for atoms, preparation of atomic number states, and controlled atomic entanglement. In our sodium experiment we focus on the study of many-body quantum transport. Our system consists of a BEC confined to a hybrid magnetic/optical trap.~ Transverse confinement is provided by a 2-D axially symmetric magnetic trap and the BEC is confined axially by two focused spots that are separated by a controlled distance, creating an optical box.~ The atoms are then released into an optical potential along the axial direction that is created by an array of far detuned laser spots.~ Each spot~ can be independently controlled both in position and power, with a spatial resolution of six microns.~ This potential can be combined with a standing wave that is aligned along the trap axis, enabling transport measurements in potentials that can range from periodic to disordered. Finally, I will discuss recent ideas on constructing an optical ``one-way'' barrier for atoms.~ I will show how this idea can be used for phase space compression and cooling, as an optical realization of Maxwell's demon. [Preview Abstract] |
Friday, May 20, 2005 3:54PM - 4:30PM |
L1.00005: Demonstration of small quantum algorithms in an ion trap array Invited Speaker: Atomic ions confined in an array of traps represent a potentially scalable approach to quantum information processing. All of the basic requirements have been demonstrated in one and two qubit experiments. The remaining task is to scale the system to hundreds and later thousands of qubits while minimizing and correcting errors in the system. While this requires extremely challenging technological improvements, no fundamental roadblocks are currently foreseen. I will give a survey of recent progress in implementing simple two and three-qubit quantum algorithms with ions in trap arrays. In particular, implementations of quantum teleportation,~quantum error correction and the quantum Fourier transform will be discussed. I will also summarize the prospects and challenges of scaling this particular approach towards a large scale computing device. [Preview Abstract] |
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