8,823 research outputs found
Clinical features of varicella-zoster virus infection
Varicella-zoster virus (VZV) is a pathogenic human herpes virus that causes varicella (chickenpox) as a primary infection, following which it becomes latent in peripheral ganglia. Decades later, the virus may reactivate either spontaneously or after a number of triggering factors to cause herpes zoster (shingles). Varicella and its complications are more severe in the immunosuppressed. The most frequent and important complication of VZV reactivation is postherpetic neuralgia, the cause of which is unknown and for which treatment is usually ineffective. Reactivation of VZV may also cause a wide variety of neurological syndromes, the most significant of which is a vasculitis, which is treated with corticosteroids and the antiviral drug acyclovir. Other VZV reactivation complications include an encephalitis, segmental motor weakness and myelopathy, cranial neuropathies, Guillain–Barré syndrome, enteric features, and zoster sine herpete, in which the viral reactivation occurs in the absence of the characteristic dermatomally distributed vesicular rash of herpes zoster. There has also been a recent association of VZV with giant cell arteritis and this interesting finding needs further corroboration. Vaccination is now available for the prevention of both varicella in children and herpes zoster in older individuals
Maximizing information on the environment by dynamically controlled qubit probes
We explore the ability of a qubit probe to characterize unknown parameters of
its environment. By resorting to quantum estimation theory, we analytically
find the ultimate bound on the precision of estimating key parameters of a
broad class of ubiquitous environmental noises ("baths") which the qubit may
probe. These include the probe-bath coupling strength, the correlation time of
generic bath spectra, the power laws governing these spectra, as well as their
dephasing times T2. Our central result is that by optimizing the dynamical
control on the probe under realistic constraints one may attain the maximal
accuracy bound on the estimation of these parameters by the least number of
measurements possible. Applications of this protocol that combines dynamical
control and estimation theory tools to quantum sensing are illustrated for a
nitrogen-vacancy center in diamond used as a probe.Comment: 8 pages + 6 pages (appendix), 3 Figure
Criticality of environmental information obtainable by dynamically controlled quantum probes
A universal approach to decoherence control combined with quantum estimation
theory reveals a critical behavior, akin to a phase transition, of the
information obtainable by a qubit probe concerning the memory time of
environmental fluctuations. This criticality emerges only when the probe is
subject to dynamical control. It gives rise to a sharp transition between two
dynamical phases characterized by either a short or long memory time compared
to the probing time. This phase-transition of the environmental information is
a fundamental feature that facilitates the attainment of the highest estimation
precision of the environment memory-time and the characterization of probe
dynamics.Comment: 3 pages, 4 figure
Physics at SuperB
Flavour will play a crucial role in understanding physics beyond the Standard
Model. Progress in developing a future programme to investigate this central
area of particle physics has recently passed a milestone, with the completion
of the conceptual design report for SuperB, a very high luminosity, asymmetric
e+e- collider. This article summarizes the important role of SuperB in
understanding new physics in the LHC era.Comment: 4 pages, 2 figures. To appear in the proceedings of the International
Europhysics Conference on High Energy Physics (EPS-HEP2007), Manchester,
England, 19-25 July 200
Optimal Dynamical Decoherence Control of a Qubit
A theory of dynamical control by modulation for optimal decoherence reduction
is developed. It is based on the non-Markovian Euler-Lagrange equation for the
energy-constrained field that minimizes the average dephasing rate of a qubit
for any given dephasing spectrum.Comment: 6 pages, including 2 figures and an appendi
Zeno and anti-Zeno polarization control of spin-ensembles by induced dephasing
We experimentally and theoretically demonstrate the purity (polarization)
control of qubits entangled with multiple spins, using induced dephasing in
nuclear magnetic resonance (NMR) setups to simulate repeated quantum
measurements. We show that one may steer the qubit ensemble towards a
quasi-equilibrium state of certain purity, by choosing suitable time intervals
between dephasing operations. These results demonstrate that repeated dephasing
at intervals associated with the anti-Zeno regime lead to ensemble
purification, whereas those associated with the Zeno regime lead to ensemble
mixing.Comment: Main Text: 5 pages, 2 figures. Sup. Inf.: 5pages, 1 figur
Optimizing inhomogeneous spin ensembles for quantum memory
We propose a general method to maximize the fidelity of writing, storage and
reading of quantum information (QI) in a spectrally inhomogeneous spin ensemble
used as quantum memory. The method is based on preselecting the optimal
spectral portion of the ensemble by a judiciously designed pulse. It allows
drastic improvement of quantum memory realized by spin ensembles that store QI
from a resonator or an optical beam.Comment: Corrected m
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