880 research outputs found
5KW pulse width modulated static inverter
Design verification tests for logic and low level circuits, and preliminary single-phase breadboard of pulse width modulated static inverte
Intervertebral disc embolization resulting in spinal cord infarction
Journal ArticleA case of spinal cord infarction resulting from embolization of fibrocartilaginous intervertebral disc material is presented. Cases from the literature are reviewed and the theories of pathogenesis are discussed. In all reported cases the diagnosis was not made until postmortem examination
J Fluorescence
The scope of this paper is to illustrate the need for an improved quality assurance in fluorometry. For this purpose, instrumental sources of error and their influences on the reliability and comparability of fluorescence data are highlighted for frequently used photoluminescence techniques ranging from conventional macro- and microfluorometry over fluorescence microscopy and flow cytometry to microarray technology as well as in vivo fluorescence imaging. Particularly, the need for and requirements on fluorescence standards for the characterization and performance validation of fluorescence instruments, to enhance the comparability of fluorescence data, and to enable quantitative fluorescence analysis are discussed. Special emphasis is dedicated to spectral fluorescence standards and fluorescence intensity standards
Violation of Bell's Inequality with Photons from Independent Sources
We report a violation of Bell's inequality using one photon from a parametric
down-conversion source and a second photon from an attenuated laser beam. The
two photons were entangled at a beam splitter using the post-selection
technique of Shih and Alley [Phys. Rev. Lett. 61, 2921 (1988)]. A quantum
interference pattern with a visibility of 91% was obtained using the photons
from these independent sources, as compared with a visibility of 99.4% using
two photons from a central parametric down-conversion source.Comment: 4 pages, 5 figures; minor change
VLBI observations of the Crab nebula pulsar
Observations were made at meter wave-lengths using very long base-line interferometry techniques. At 196.5 MHz no resolution of the pulsar are observed; all the pulse shapes observed with the interferometers are similar to single dish profiles, and all the power pulsates. At 111.5 MHz besides the pulsing power there is always a steady component, presumably due to interstellar scattering. The pulsar is slightly resolved at 111.5 MHz with an apparent angular diameter of 0.07 sec ? 0.01 sec. A 50 percent linear polarization of the time-averaged power is noted at 196.5 MHz; at 111.5 MHz, 20 percent of the total time-averaged power is polarized, 35 percent of the pulsing power is polarized, and the steady component is unpolarized
A conditional-phase switch at the single-photon level
We present an experimental realization of a two-photon conditional-phase
switch, related to the ``-'' gate of quantum computation. This gate
relies on quantum interference between photon pairs, generating entanglement
between two optical modes through the process of spontaneous parametric
down-conversion (SPDC). The interference effect serves to enhance the effective
nonlinearity by many orders of magnitude, so it is significant at the quantum
(single-photon) level. By adjusting the relative optical phase between the
classical pump for SPDC and the pair of input modes, one can impress a large
phase shift on one beam which depends on the presence or absence of a single
photon in a control mode.Comment: 8 pages, 4 figure
Entanglement-secured single-qubit quantum secret-sharing
In single-qubit quantum secret sharing, a secret is shared between N parties
via manipulation and measurement of one qubit at a time. Each qubit is sent to
all N parties in sequence; the secret is encoded in the first participant's
preparation of the qubit state and the subsequent participants' choices of
state rotation or measurement basis. We present a protocol for single-qubit
quantum secret sharing using polarization entanglement of photon pairs produced
in type-I spontaneous parametric downconversion. We investigate the protocol's
security against eavesdropping attack under common experimental conditions: a
lossy channel for photon transmission, and imperfect preparation of the initial
qubit state. A protocol which exploits entanglement between photons, rather
than simply polarization correlation, is more robustly secure. We implement the
entanglement-based secret-sharing protocol with 87% secret-sharing fidelity,
limited by the purity of the entangled state produced by our present apparatus.
We demonstrate a photon-number splitting eavesdropping attack, which achieves
no success against the entanglement-based protocol while showing the predicted
rate of success against a correlation-based protocol.Comment: 10 pages, 8 figure
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