289 research outputs found
Quantum cryptography using balanced homodyne detection
We report an experimental quantum key distribution that utilizes balanced
homodyne detection, instead of photon counting, to detect weak pulses of
coherent light. Although our scheme inherently has a finite error rate, it
allows high-efficiency detection and quantum state measurement of the
transmitted light using only conventional devices at room temperature. When the
average photon number was 0.1, an error rate of 0.08 and "effective" quantum
efficiency of 0.76 were obtained.Comment: Errors in the sentence citing ref.[20] are correcte
On quantum teleportation with beam-splitter-generated entanglement
Following the lead of Cochrane, Milburn, and Munro [Phys. Rev. A {\bf 62},
062307 (2000)], we investigate theoretically quantum teleportation by means of
the number-sum and phase-difference variables. We study Fock-state entanglement
generated by a beam splitter and show that two-mode Fock-state inputs can be
entangled by a beam splitter into close approximations of maximally entangled
eigenstates of the phase difference and the photon-number sum
(Einstein-Podolsky-Rosen -- EPR -- states). Such states could be experimentally
feasible with on-demand single-photon sources. We show that the teleportation
fidelity can reach near unity when such ``quasi-EPR'' states are used as the
quantum channel.Comment: 7 pages (two-column), 7 figures, submitted to Phys. Rev. A. Text
unmodified, postscript error correcte
Resonances in the three-neutron system
A study of 3-body resonances has been performed in the framework of
configuration space Faddeev equations. The importance of keeping a sufficient
number of terms in the asymptotic expansion of the resonance wave function is
pointed out. We investigated three neutrons interacting in selected force
components taken from realistic nn forces.Comment: 38 pages, 11 tables, 4 figure
Nonclassical statistics of intracavity coupled waveguides: the quantum optical dimer
A model is proposed where two nonlinear waveguides are contained
in a cavity suited for second-harmonic generation. The evanescent wave coupling
between the waveguides is considered as weak, and the interplay between this
coupling and the nonlinear interaction within the waveguides gives rise to
quantum violations of the classical limit. These violations are particularly
strong when two instabilities are competing, where twin-beam behavior is found
as almost complete noise suppression in the difference of the fundamental
intensities. Moreover, close to bistable transitions perfect twin-beam
correlations are seen in the sum of the fundamental intensities, and also the
self-pulsing instability as well as the transition from symmetric to asymmetric
states display nonclassical twin-beam correlations of both fundamental and
second-harmonic intensities. The results are based on the full quantum Langevin
equations derived from the Hamiltonian and including cavity damping effects.
The intensity correlations of the output fields are calculated
semi-analytically using a linearized version of the Langevin equations derived
through the positive-P representation. Confirmation of the analytical results
are obtained by numerical simulations of the nonlinear Langevin equations
derived using the truncated Wigner representation.Comment: 15 pages, 8 figures, submitted to Phys. Rev.
Complete solutions to the metric of spherically collapsing dust in an expanding spacetime with a cosmological constant
We present semi-analytical solutions to the background equations describing
the Lema\^itre-Tolman-Bondi (LTB) metric as well as the homogeneous Friedmann
equations, in the presence of dust, curvature and a cosmological constant
Lambda. For none of the presented solutions any numerical integration has to be
performed. All presented solutions are given for expanding and collapsing
phases, preserving continuity in time and radius. Hence, these solutions
describe the complete space time of a collapsing spherical object in an
expanding universe. In the appendix we present for completeness a solution of
the Friedmann equations in the additional presence of radiation, only valid for
the Robertson-Walker metric.Comment: 23 pages, one figure. Numerical module for evaluation of the
solutions released at
http://web.physik.rwth-aachen.de/download/valkenburg/ColLambda/ Matches
published version, published under Open Access. Note change of titl
The Two-Nucleon Potential from Chiral Lagrangians
Chiral symmetry is consistently implemented in the two-nucleon problem at
low-energy through the general effective chiral lagrangian. The potential is
obtained up to a certain order in chiral perturbation theory both in momentum
and coordinate space. Results of a fit to scattering phase shifts and bound
state data are presented, where satisfactory agreement is found for laboratory
energies up to about 100 Mev.Comment: Postscript file; figures available by reques
Continuous variable entanglement and quantum state teleportation between optical and macroscopic vibrational modes through radiation pressure
We study an isolated, perfectly reflecting, mirror illuminated by an intense
laser pulse. We show that the resulting radiation pressure efficiently
entangles a mirror vibrational mode with the two reflected optical sideband
modes of the incident carrier beam. The entanglement of the resulting
three-mode state is studied in detail and it is shown to be robust against the
mirror mode temperature. We then show how this continuous variable entanglement
can be profitably used to teleport an unknown quantum state of an optical mode
onto the vibrational mode of the mirror.Comment: 18 pages, 10 figure
Magnetoluminescence
Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain
regions where the electromagnetic energy density greatly exceeds the plasma
energy density. These sources exhibit dramatic flaring activity where the
electromagnetic energy distributed over large volumes, appears to be converted
efficiently into high energy particles and gamma-rays. We call this general
process magnetoluminescence. Global requirements on the underlying, extreme
particle acceleration processes are described and the likely importance of
relativistic beaming in enhancing the observed radiation from a flare is
emphasized. Recent research on fluid descriptions of unstable electromagnetic
configurations are summarized and progress on the associated kinetic
simulations that are needed to account for the acceleration and radiation is
discussed. Future observational, simulation and experimental opportunities are
briefly summarized.Comment: To appear in "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts
and Blazars: Physics of Extreme Energy Release" of the Space Science Reviews
serie
First observation of the decay and a measurement of the ratio of branching fractions
The first observation of the decay using
data collected by the LHCb detector at a centre-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 36 pb, is reported. A
signal of events is obtained and the absence of signal is
rejected with a statistical significance of more than nine standard deviations.
The branching fraction is measured relative to
that of : , where the first uncertainty is statistical, the second systematic and
the third is due to the uncertainty on the ratio of the and
hadronisation fractions.Comment: 10 pages, 3 figures, submitted to Phys. Lett. B; ISSN 0370-269
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