Coherent State Quantum Key Distribution with Entanglement Witnessing

An entanglement witness approach to quantum coherent state key distribution and a system for its practical implementation are described. In this approach, eavesdropping can be detected by a change in sign of either of two witness functions, an entanglement witness S or an eavesdropping witness W. The effects of loss and eavesdropping on system operation are evaluated as a function of distance. Although the eavesdropping witness W does not directly witness entanglement for the system, its behavior remains related to that of the true entanglement witness S. Furthermore, W is easier to implement experimentally than S. W crosses the axis at a finite distance, in a manner reminiscent of entanglement sudden death. The distance at which this occurs changes measurably when an eavesdropper is present. The distance dependance of the two witnesses due to amplitude reduction and due to increased variance resulting from both ordinary propagation losses and possible eavesdropping activity is provided. Finally, the information content and secure key rate of a continuous variable protocol using this witness approach are given

The Antecedents of Community Commitment in Online Communities of Practice

Online Communities of Practice offer their members the ability to communicate about a topic of interest in a way that transcends the limitations of geography. However, many communities of practice fail due to a lack of community commitment. This research examines the types of commitments that group members make to a community and what factors influence members to make a commitment to the community. A community commitment survey was distributed to online communities of practice. The results suggest that members make continuance (need-based), affective (emotion-based) and normative (obligation-based) commitments to the online communities of practice. Usefulness and system reliability lead members to make a continuance commitment. Social interaction and identification encourage members to make an affective commitment. Positive social influence and altruism influence members to make a normative commitment. The implications of this research for practitioners are discussed

Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring

Spontaneous excitation of the dominant mode in a spin-wave active ring -- a self-exciting positive-feedback system incorporating a spin-wave transmission structure -- occurs at a certain threshold value of external gain. In general, the wavenumber of the dominant mode is extremely sensitive to the properties and environment of the spin-wave transmission medium, and is almost impossible to predict. In this letter, we report on a backward volume magnetostatic spin-wave active ring system incorporating a magnonic crystal. When mode enhancement conditions -- readily predicted by a theoretical model -- are satisfied, the ring geometry permits highly robust and consistent forced dominant wavenumber selection.Comment: 4 pages, 3 figure

Kolmogorov Similarity Hypotheses for Scalar Fields: Sampling Intermittent Turbulent Mixing in the Ocean and Galaxy

Kolmogorov's three universal similarity hypotheses are extrapolated to describe scalar fields like temperature mixed by turbulence. By the analogous Kolmogorov third hypothesis for scalars, temperature dissipation rates chi averaged over lengths r > L_K should be lognormally distributed with intermittency factors I that increase with increasing turbulence energy length scales L_O as I_chi-r = m_T ln(L_O/r). Tests of Kolmogorovian velocity and scalar universal similarity hypotheses for very large ranges of turbulence length and time scales are provided by data from the ocean and the Galactic interstellar medium. The universal constant for turbulent mixing intermittency m_T is estimated from oceanic data to be 0.44+-0.01, which is remarkably close to estimates for Kolmogorov's turbulence intermittency constant m_u of 0.45+-0.05 from Galactic as well as atmospheric data. Extreme intermittency complicates the oceanic sampling problem, and may lead to quantitative and qualitative undersampling errors in estimates of mean oceanic dissipation rates and fluxes. Intermittency of turbulence and mixing in the interstellar medium may be a factor in the formation of stars.Comment: 23 pages original of Proc. Roy. Soc. article, 8 figures; in "Turbulence and Stochastic Processes: Kolmogorov's ideas 50 years on", London The Royal Society, 1991, J.C.R. Hunt, O.M. Phillips, D. Williams Eds., pages 1-240, vol. 434 (no. 1890) Proc. Roy. Soc. Lond. A, PDF fil

Exploring the origin of neutron star magnetic field: magnetic properties of the progenitor OB stars

Ferrario & Wickramasinghe (2006) explored the hypothesis that the magnetic fields of neutron stars are of fossil origin. In this context, they predicted the field distribution of the progenitor OB stars, finding that 5 per cent of main sequence massive stars should have fields in excess of 1kG. We have carried out sensitive ESPaDOnS spectropolarimetric observations to search for direct evidence of such fields in all massive B- and O-type stars in the Orion Nebula Cluster star-forming region. We have detected unambiguous Stokes V Zeeman signatures in spectra of three out of the eight stars observed (38%). Using a new state-of-the-art Bayesian analysis, we infer the presence of strong (kG), organised magnetic fields in their photospheres. For the remaining five stars, we constrain any dipolar fields in the photosphere to be weaker than about 200G. Statistically, the chance of finding three ~kG fields in a sample of eight OB stars is quite low (less than 1%) if the predictions of Ferrario & Wickramasinghe are correct. This implies that either the magnetic fields of neutron stars are not of fossil origin, that the flux-evolution model of Ferrario & Wickramasinghe is incomplete, or that the ONC has unusual magnetic properties. We are undertaking a study of other young star clusters, in order to better explore these possibilities.Comment: 40 Years of Pulsars conference: Millisecond Pulsars, Magnetars and More. McGill University, Montreal, Canada, August 12-17, 2007. 5 pages, 4 figure

Bohm's quantum potential and quantum force in superconductor

The Bohm's quantum potential, introduced in 1952, and the quantum force in superconductor, introduced in 2001, allow to describe non-local force-free momentum transfer observed in the Ahronov-Bohm effects. Comparison of the Ahronov-Bohm effects in the two-slit interference experiment and in superconductor ring reveals fundamental difference between the Schrodinger wave function and the wave function describing macroscopic quantum phenomena. The Ginzburg-Landau wave function describing the superconductivity phenomenon can not collapse and an additional postulate, which was implied first by L.D. Landau, must be used for the description of macroscopic quantum phenomena. It is note that quantum principles and postulates should not be universal till the quantum formalism is only phenomenological theory but no description of an unique reality. A simple Gedankenexperiment is considered which challenges the universality of the Heisenberg uncertainty relation and the Bohr's complementarity principle.Comment: 9 pages, 1 figure, the Invited talk was presented at the conference "Foundations of Probability and Physics-5" Vaxjo University, Sweden, August 24-27, 200

Observation of Interaction of Spin and Intrinsic Orbital Angular Momentum of Light

Interaction of spin and intrinsic orbital angular momentum of light is observed, as evidenced by length-dependent rotations of both spatial patterns and optical polarization in a cylindrically-symmetric isotropic optical fiber. Such rotations occur in straight few-mode fiber when superpositions of two modes with parallel and anti-parallel orientation of spin and intrinsic orbital angular momentum (IOAM=$2\hslash$) are excited, resulting from a degeneracy splitting of the propagation constants of the modes.Comment: 6 pages, 5 figures, and a detailed supplement. Version 3 corrects a typo and adds the journal referenc

Silica in a Mars analog environment: Ka'u Desert, Kilauea Volcano, Hawaii

Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS) data acquired over the Ka'u Desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials, including 250–700 and 200–400 year old lava flows, 1971 and 1974 flows, ash deposits, and solfatara incrustations. To provide context, a geologic surface units map is constructed, verified with field observations, and supported by laboratory analyses. AVIRIS spectral end-members are identified in the visible (0.4 to 1.2 μm) and short wave infrared (2.0 to 2.5 μm) wavelength ranges. Nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene, olivine, hematite, goethite, and poorly crystalline iron oxides or glass. A broad, nearly ubiquitous absorption feature centered at 2.25 μm is attributed to opaline (amorphous, hydrated) silica and is found to correlate spatially with mapped geologic surface units. Laboratory analyses show the silica to be consistently present as a deposited phase, including incrustations downwind from solfatara vents, cementing agent for ash duricrusts, and thin coatings on the youngest lava flow surfaces. A second, Ti-rich upper coating on young flows also influences spectral behavior. This study demonstrates that secondary silica is mobile in the Ka'u Desert on a variety of time scales and spatial domains. The investigation from remote, field, and laboratory perspectives also mimics exploration of Mars using orbital and landed missions, with important implications for spectral characterization of coated basalts and formation of opaline silica in arid, acidic alteration environments

Oscillatory Energy Exchange Between Waves Coupled by a Dynamic Artificial Crystal

We describe a general mechanism of controllable energy exchange between waves propagating in a dynamic artificial crystal. We show that if a spatial periodicity is temporarily imposed on the transmission properties of a wave-carrying medium whilst a wave is inside, this wave is coupled to a secondary counter-propagating wave and energy oscillates between the two. The oscillation frequency is determined by the width of the spectral band gap created by the periodicity and the frequency difference between the coupled waves. The effect is demonstrated with spin waves in a dynamic magnonic crystal.Comment: 5 pages, 4 figure