26,772 research outputs found
Nonlocal memory assisted entanglement distribution in optical fibers
Successful implementation of several quantum information and communication
protocols require distributing entangled pairs of quantum bits in reliable
manner. While there exists a substantial amount of recent theoretical and
experimental activities dealing with non-Markovian quantum dynamics,
experimental application and verification of the usefulness of memory-effects
for quantum information tasks is still missing. We combine these two aspects
and show experimentally that a recently introduced concept of nonlocal memory
effects allows to protect and distribute polarization entangled pairs of
photons in efficient manner within polarization-maintaining (PM) optical
fibers. The introduced scheme is based on correlating the environments, i.e.
frequencies of the polarization entangled photons, before their physical
distribution. When comparing to the case without nonlocal memory effects, we
demonstrate at least 12-fold improvement in the channel, or fiber length, for
preserving the highly-entangled initial polarization states of photons against
dephasing
Photon temporal modes: a complete framework for quantum information science
Field-orthogonal temporal modes of photonic quantum states provide a new
framework for quantum information science (QIS). They intrinsically span a
high-dimensional Hilbert space and lend themselves to integration into existing
single-mode fiber communication networks. We show that the three main
requirements to construct a valid framework for QIS -- the controlled
generation of resource states, the targeted and highly efficient manipulation
of temporal modes and their efficient detection -- can be fulfilled with
current technology. We suggest implementations of diverse QIS applications
based on this complete set of building blocks.Comment: 17 pages, 13 figure
The effect of realistic geometries on the susceptibility-weighted MR signal in white matter
Purpose: To investigate the effect of realistic microstructural geometry on
the susceptibility-weighted magnetic resonance (MR) signal in white matter
(WM), with application to demyelination.
Methods: Previous work has modeled susceptibility-weighted signals under the
assumption that axons are cylindrical. In this work, we explore the
implications of this assumption by considering the effect of more realistic
geometries. A three-compartment WM model incorporating relevant properties
based on literature was used to predict the MR signal. Myelinated axons were
modeled with several cross-sectional geometries of increasing realism: nested
circles, warped/elliptical circles and measured axonal geometries from electron
micrographs. Signal simulations from the different microstructural geometries
were compared to measured signals from a Cuprizone mouse model with varying
degrees of demyelination.
Results: Results from simulation suggest that axonal geometry affects the MR
signal. Predictions with realistic models were significantly different compared
to circular models under the same microstructural tissue properties, for
simulations with and without diffusion.
Conclusion: The geometry of axons affects the MR signal significantly.
Literature estimates of myelin susceptibility, which are based on fitting
biophysical models to the MR signal, are likely to be biased by the assumed
geometry, as will any derived microstructural properties.Comment: Accepted March 4 2017, in publication at Magnetic Resonance in
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