570 research outputs found
Perturbations of critical values in nonsmooth critical point theory
* Supported by Ministero dell’Università e della Ricerca Scientifica e Tecnologica (40% – 1993).
** Supported by Ministero dell’Università e della Ricerca Scientifica e Tecnologica (40% – 1993).The perturbation of critical values for continuous functionals is studied.
An application to eigenvalue problems for variational inequalities is provided
Dephasing due to nonstationary 1/f noise
Motivated by recent experiments with Josephson qubits we propose a new
phenomenological model for 1/f noise due to collective excitations of
interacting defects in the qubit's environment. At very low temperatures the
effective dynamics of these collective modes are very slow leading to
pronounced non-Gaussian features and nonstationarity of the noise. We analyze
the influence of this noise on the dynamics of a qubit in various regimes and
at different operation points. Remarkable predictions are absolute time
dependences of a critical coupling and of dephasing in the strong coupling
regime.Comment: 4 pages, 2 figures, to be published in the proceedings of the Vth
Rencontres de Moriond in Mesoscopic Physic
Quantum Correlation Bounds for Quantum Information Experiments Optimization: the Wigner Inequality Case
Violation of modified Wigner inequality by means binary bipartite quantum
system allows the discrimination between the quantum world and the classical
local-realistic one, and also ensures the security of Ekert-like quantum key
distribution protocol. In this paper we study both theoretically and
experimentally the bounds of quantum correlation associated to the modified
Wigner's inequality finding the optimal experimental configuration for its
maximal violation. We also extend this analysis to the implementation of
Ekert's protocol
Diffeomorphism-invariant properties for quasi-linear elliptic operators
For quasi-linear elliptic equations we detect relevant properties which
remain invariant under the action of a suitable class of diffeomorphisms. This
yields a connection between existence theories for equations with degenerate
and non-degenerate coerciveness.Comment: 16 page
Toward third order ghost imaging with thermal light
Recently it has been suggested that an enhancement in the visibility of ghost
images obtained with thermal light can be achieved exploiting higher order
correlations [3]. This paper reports on the status of an higher order ghost
imaging experiment carried on at INRIM labs exploiting a pseudo-thermal source
and a CCD camera.Comment: To be published in Proceedings of Recent advances in Foundations of
Quantum Mechanics and Quantum Informatio
Revealing interference by continuous variable discordant states
In general, a pair of uncorrelated Gaussian states mixed in a beam splitter
produces a correlated state at the output. However, when the inputs are
identical Gaussian states the output state is equal to the input, and no
correlations appear, as the interference had not taken place. On the other
hand, since physical phenomena do have observable effects, and the beam
splitter is there, a question arises on how to reveal the interference between
the two beams. We prove theoretically and demonstrate experimentally that this
is possible if at least one of the two beams is prepared in a discordant, i.e.
Gaussian correlated, state with a third beam. We also apply the same technique
to reveal the erasure of polarization information. Our experiments involves
thermal states and the results show that Gaussian discordant states, even when
they show a positive Glauber P-function, may be useful to achieve specific
tasks.Comment: published versio
Two-mode squeezed vacuum and squeezed light in correlated interferometry
We study in detail a system of two interferometers aimed to the detection of
extremely faint phase-fluctuations. This system can represent a breakthrough
for detecting a faint correlated signal that would remain otherwise
undetectable even using the most sensitive individual interferometric devices,
that are limited by the shot noise. If the two interferometers experience
identical phase-fluctuations, like the ones introduced by the so called
"holographic noise", this signal should emerge if their output signals are
correlated, while the fluctuations due to shot noise and other independent
contributions will vanish. We show how the injecting quantum light in the free
ports of the interferometers can reduce the photon noise of the system beyond
the shot-noise, enhancing the resolution in the phase-correlation estimation.
We analyze both the use of two-mode squeezed vacuum or twin-beam state (TWB)
and of two independent squeezing states. Our results basically confirms the
benefit of using squeezed beams together with strong coherent beams in
interferometry, even in this correlated case. However, mainly we concentrate on
the possible use of TWB, discovering interesting and probably unexplored areas
of application of bipartite entanglement and in particular the possibility of
reaching in principle surprising uncertainty reduction
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