Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session L4: DCMP / GQI Prize Session |
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Sponsoring Units: DCMP GQI Chair: Allen Goldman, University of Minnesota Room: Colorado Convention Center Korbel 2B-3B |
Tuesday, March 6, 2007 2:30PM - 3:06PM |
L4.00001: Quantum Measurement with the Josephson Bifurcation Amplifier Invited Speaker: The Josephson tunnel junction is a unique dipolar circuit element which can be both non-linear and non-dissipative. This combination makes it well suited to measuring quantum systems since non-linearity enables fast, sensitive detection while the absence of dissipation reduces loss of coherence. When the junction is driven close to a bifurcation point with a sufficiently intense microwave drive, then two metastable states exist which differ in oscillation amplitude and phase. The junction remains confined to a single well of its sinusoidal potential in both of these states and no DC voltage is generated. The oscillation state of the junction can be determined by measuring either the reflected or transmitted AC microwave drive signal. The transition between these dynamical states is a sensitive function of the junction critical current. Therefore, the critical current serves as the input variable of the amplifier and can be modulated by the application of a magnetic flux, electric charge, or a superconducting phase. The bifurcation amplifier has been successfully used for the state readout of superconducting qubits, and has many potential applications including the coherent detection of magnetic nanostructures such as single molecule magnets. [Preview Abstract] |
Tuesday, March 6, 2007 3:06PM - 3:42PM |
L4.00002: Prize for Research at an Undergraduate Institution Talk: A Discrete Wigner Function Invited Speaker: For a quantum particle moving in one dimension, the Wigner function represents the particle's quantum state as a real function on the two-dimensional phase space. Though the Wigner function typically takes negative values and can therefore not be interpreted as a probability distribution, its integral along any axis in phase space---even a skew axis---is in fact the probability distribution of an observable associated with that axis. A number of authors have developed generalizations of the Wigner function that apply to discrete quantum systems, but such generalizations are often problematic when the state-space dimension is even. Here we present a discrete Wigner function that shares with the continuous Wigner function the ``tomographic'' property described above, and is well suited to describe a system of binary quantum objects. We discuss potential applications to quantum computation and quantum cryptography. [Preview Abstract] |
Tuesday, March 6, 2007 3:42PM - 4:18PM |
L4.00003: Atoms in a Cavity: A Source of Narrowband Photon Pairs Invited Speaker: Coupling atoms to an optical cavity can significantly enhance the directionality of photon emission from atoms. Using such an atoms-cavity system, we have created a high-brightness source of narrowband, identical-photon pairs. The source was applied to two experiments: interferometry and entanglement. Biphoton interferometry holds promise to demonstrate precision beyond the shot noise limit, although the measured interference fringe visibility of 0.84 $\pm$ 0.04 only translated to a shot noise limited phase uncertainty. Polarization-time entangled photon pairs were also directly generated via an adjusted optical pumping scheme for the atoms. [Preview Abstract] |
Tuesday, March 6, 2007 4:18PM - 4:54PM |
L4.00004: Low-temperature infrared spectroscopy of H$_2$ in solid C$_{60}$ Invited Speaker: Diffuse reflectance infrared spectroscopy was used to probe the quantum dynamics of H$_2$ trapped in a C$_{60}$ lattice. Because free H$_2$ is infrared inactive, features of the infrared spectra are induced solely through interactions with the host material and as such provide detailed information about the potential at the binding site. The design and construction of a cryogenic apparatus allowed the extension of previous room temperature measurements to temperatures as low as 10 K at pressures as high as 100 atm. The low temperature spectra contained much sharper peaks and a rich fine structure, enabling more precise determination of the details of the C$_{60}$-H$_{2}$ interaction potential. These studies of H$_2$ in C$_{60}$ inform hydrogen storage materials research in a broader context, as illustrated by the diffuse reflectance spectra of H$_2$ in MOF-5. [Preview Abstract] |
Tuesday, March 6, 2007 4:54PM - 5:30PM |
L4.00005: Maximum entropy-principle approach to quantum storage in strongly correlated systems Invited Speaker: We shall investigate whether it is possible to generate QUBITS and/or QUTRITS starting with a modified version of Hubbard-Anderson Hamiltonian pertinent to describe magnetic properties of strongly correlated systems, particularly manganites. For this purpose, we shall derive the expressions for expectation values of a set of relevant operators starting with the Shanon entropy and using maximum entropy principle. It also allows us to derive Weiss relation that relates the spin-projection at a site to the interaction of that site with the rest of the medium. In the presence of an internal or applied magnetic field, or both, the absolute minima of free energy for spin projection in z-direction is +1, 0 and -1 for a triplet pair of fermion at three different temperatures, which are identified as QUBITS (in case one does not distinguish between $\pm 1$ projections) or QUTRITS. [Preview Abstract] |
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