177 research outputs found
Mitogen-induced oscillations of membrane potential and Ca2+ in human fibroblasts
AbstractUsing the whole-cell technique, we have measured recurring hyperpolarizations induced by fetal calf serum and bradykinin in human fibroblasts. By coupling fura-2 microfluorimetry to electrophysiology, we have also measured directly cytosolic Ca2+ and found that Ca2+ oscillations occur in synchrony with membrane currents. Mitogen stimulation of cells in which intracellular K+ had been replaced with Cs+ resulted in the abolishment of the outward current. We conclude then that the mitogen-induced recurring hyperpolarizations in human fibroblasts are due to the opening of Ca2+-activated K+ channels
Effect of noise and enhancement of nonlocality in on/off photodetection
Nonlocality of two-mode states of light is addressed by means of CHSH
inequality based on displaced on/off photodetection. Effects due to non-unit
quantum efficiency and nonzero dark counts are taken into account. Nonlocality
of both balanced and unbalanced superpositions of few photon-number states, as
well as that of multiphoton twin beams, is investigated. We find that
unbalanced superpositions show larger nonlocality than balanced one when noise
affects the photodetection process. De-Gaussification by means of
(inconclusive) photon subtraction is shown to enhance nonlocality of twin beams
in the low energy regime. We also show that when the measurement is described
by a POVM, rather than a set of projectors, the maximum achievable value of the
Bell parameter in the CHSH inequality is decreased, and is no longer given by
the Cirel'son bound.Comment: 21 Figure
The Quantum Separability Problem for Gaussian States
Determining whether a quantum state is separable or entangled is a problem of
fundamental importance in quantum information science. This is a brief review
in which we consider the problem for states in infinite dimensional Hilbert
spaces. We show how the problem becomes tractable for a class of Gaussian
states.Comment: 8 page
Optimized teleportation in Gaussian noisy channels
We address continuous variable quantum teleportation in Gaussian quantum
noisy channels, either thermal or squeezed-thermal. We first study the
propagation of twin-beam and evaluate a threshold for its separability. We find
that the threshold for purely thermal channels is always larger than for
squeezed-thermal ones. On the other hand, we show that squeezing the channel
improves teleportation of squeezed states and, in particular, we find the class
of squeezed states that are better teleported in a given noisy channel.
Finally, we find regimes where optimized teleportation of squeezed states
improves amplitude-modulated communication in comparison with direct
transmission
Characterizing the entanglement of bipartite quantum systems
We derive a separability criterion for bipartite quantum systems which
generalizes the already known criteria. It is based on observables having
generic commutation relations. We then discuss in detail the relation among
these criteria.Comment: 5 pages, 2 figures. Revised versio
On Relativistic Quantum Information Properties of Entangled Wave Vectors of Massive Fermions
We study special relativistic effects on the entanglement between either
spins or momenta of composite quantum systems of two spin-1/2 massive
particles, either indistinguishable or distinguishable, in inertial reference
frames in relative motion. For the case of indistinguishable particles, we
consider a balanced scenario where the momenta of the pair are well-defined but
not maximally entangled in the rest frame while the spins of the pair are
described by a one-parameter () family of entangled bipartite states. For
the case of distinguishable particles, we consider an unbalanced scenario where
the momenta of the pair are well-defined and maximally entangled in the rest
frame while the spins of the pair are described by a one-parameter ()
family of non-maximally entangled bipartite states. In both cases, we show that
neither the spin-spin () nor the momentum-momentum () entanglements
quantified by means of Wootters' concurrence are Lorentz invariant quantities:
the total amount of entanglement regarded as the sum of these entanglements is
not the same in different inertial moving frames. In particular, for any value
of the entangling parameters, both and -entanglements are attenuated
by Lorentz transformations and their parametric rates of change with respect to
the entanglements observed in a rest frame have the same monotonic behavior.
However, for indistinguishable (distinguishable) particles, the change in
entanglement for the momenta is (is not) the same as the change in entanglement
for spins. As a consequence, in both cases, no entanglement compensation
between spin and momentum degrees of freedom occurs.Comment: 21 pages, 8 figure
Quaternionic potentials in non-relativistic quantum mechanics
We discuss the Schrodinger equation in presence of quaternionic potentials.
The study is performed analytically as long as it proves possible, when not, we
resort to numerical calculations. The results obtained could be useful to
investigate an underlying quaternionic quantum dynamics in particle physics.
Experimental tests and proposals to observe quaternionic quantum effects by
neutron interferometry are briefly reviewed.Comment: 21 pages, 16 figures (ps), AMS-Te
Quantum Characterization of a Werner-like Mixture
We introduce a Werner-like mixture [R. F. Werner, Phys. Rev. A {\bf 40}, 4277
(1989)] by considering two correlated but different degrees of freedom, one
with discrete variables and the other with continuous variables. We evaluate
the mixedness of this state, and its degree of entanglement establishing its
usefulness for quantum information processing like quantum teleportation. Then,
we provide its tomographic characterization. Finally, we show how such a
mixture can be generated and measured in a trapped system like one electron in
a Penning trap.Comment: 8 pages ReVTeX, 8 eps figure
Entangling macroscopic oscillators exploiting radiation pressure
It is shown that radiation pressure can be profitably used to entangle {\it
macroscopic} oscillators like movable mirrors, using present technology. We
prove a new sufficient criterion for entanglement and show that the achievable
entanglement is robust against thermal noise. Its signature can be revealed
using common optomechanical readout apparatus.Comment: 4 pages, 2 eps figures, new separability criterion added, new figure
2, authors list change
XIPE: the X-ray Imaging Polarimetry Explorer
X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and
temporal variability measurements and to imaging, allows a wealth of physical
phenomena in astrophysics to be studied. X-ray polarimetry investigates the
acceleration process, for example, including those typical of magnetic
reconnection in solar flares, but also emission in the strong magnetic fields
of neutron stars and white dwarfs. It detects scattering in asymmetric
structures such as accretion disks and columns, and in the so-called molecular
torus and ionization cones. In addition, it allows fundamental physics in
regimes of gravity and of magnetic field intensity not accessible to
experiments on the Earth to be probed. Finally, models that describe
fundamental interactions (e.g. quantum gravity and the extension of the
Standard Model) can be tested. We describe in this paper the X-ray Imaging
Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a
small mission with a launch in 2017 but not selected. XIPE is composed of two
out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD)
filled with a He-DME mixture at their focus and two additional GPDs filled with
pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 %
at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half
Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X
optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with
Malindi as down-link station and of a Mission Operation Center (MOC) at INPE
(Brazil).Comment: 49 pages, 14 figures, 6 tables. Paper published in Experimental
Astronomy http://link.springer.com/journal/1068
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