11,546 research outputs found
A single atom-based generation of Bell states of two cavities
A new conditional scheme for generating Bell states of two spatially
separated high-Q cavities is reported. Our method is based on the passage of
one atom only through the two cavities. A distinctive feature of our treatment
is that it incorporates from the very beginning the unavoidable presence of
fluctuations in the atom-cavity interaction times. The possibility of
successfully implementing our proposal against cavity losses and atomic
spontaneous decay is carefully discussed
Genuine Tripartite Entanglement in a Spin-Star Network at Thermal Equilibrium
In a recent paper [M. Huber {\it et al}, Phys. Rev. Lett. {\bf 104}, 210501
(2010)] new criteria to find out the presence of multipartite entanglement have
been given. We exploit these tools in order to study thermal entanglement in a
spin-star network made of three peripheral spins interacting with a central
one. Genuine tripartite entanglement is found in a wide range of the relevant
parameters. A comparison between predictions based on the new criteria and on
the tripartite negativity is also given.Comment: 8 pages, 13 figure
Reconstruction of Hamiltonians from given time evolutions
In this paper we propose a systematic method to solve the inverse dynamical
problem for a quantum system governed by the von Neumann equation: to find a
class of Hamiltonians reproducing a prescribed time evolution of a pure or
mixed state of the system. Our approach exploits the equivalence between an
action of the group of evolution operators over the state space and an adjoint
action of the unitary group over Hermitian matrices. The method is illustrated
by two examples involving a pure and a mixed state.Comment: 14 page
Determination of rotation periods in solar-like stars with irregular sampling: the Gaia case
We present a study on the determination of rotation periods (P) of solar-like
stars from the photometric irregular time-sampling of the ESA Gaia mission,
currently scheduled for launch in 2013, taking into account its dependence on
ecliptic coordinates. We examine the case of solar-twins as well as thousands
of synthetic time-series of solar-like stars rotating faster than the Sun. In
the case of solar twins we assume that the Gaia unfiltered photometric passband
G will mimic the variability of the total solar irradiance (TSI) as measured by
the VIRGO experiment. For stars rotating faster than the Sun, light-curves are
simulated using synthetic spectra for the quiet atmosphere, the spots, and the
faculae combined by applying semi-empirical relationships relating the level of
photospheric magnetic activity to the stellar rotation and the Gaia
instrumental response. The capabilities of the Deeming, Lomb-Scargle, and Phase
Dispersion Minimisation methods in recovering the correct rotation periods are
tested and compared. The false alarm probability (FAP) is computed using Monte
Carlo simulations and compared with analytical formulae. The Gaia scanning law
makes the rate of correct detection of rotation periods strongly dependent on
the ecliptic latitude (beta). We find that for P ~ 1 d, the rate of correct
detection increases with ecliptic latitude from 20-30 per cent at beta ~
0{\deg} to a peak of 70 per cent at beta=45{\deg}, then it abruptly falls below
10 per cent at beta > 45{\deg}. For P > 5 d, the rate of correct detection is
quite low and for solar twins is only 5 per cent on average.Comment: 12 pages, 18 figures, accepted by MNRA
Preparation of macroscopically distinguishable superpositions of circular or linear oscillatory states of a bidimensionally trapped ion
Interaction of bimodal fields with few-level atoms in cavities and traps
The spectacular experimental results of the last few years in cavity quantum
electrodynamics and trapped ions research has led to very high level laboratory
performances. Such a stimulating situation essentially stems from two decisive
advancements. The first is the invention of reliable protocols for the
manipulation of single atoms. The second is the ability to produce desired
bosonic environments on demand. These progresses have led to the possibility of
controlling the form of the coupling between individual atoms and an arbitrary
number of bosonic modes. As a consequence, fundamental matter-radiation
interaction models like, for instance, the JC model and most of its numerous
nonlinear multiphoton generalizations, have been realized or simulated in
laboratory and their dynamical features have been tested more or less in
detail. This topical paper reviews the state of the art of the theoretical
investigations and of the experimental observations concerning the dynamical
features of the coupling between single few-level atoms and two bosonic modes.
In the course of the paper we show that such a configuration provides an
excellent platform for investigating various quantum intermode correlation
effects tested or testable in the cavity quantum electrodynamics and trapped
ion experimental realms. In particular we discuss a mode-mode correlation
effect appearing in the dynamics of a two-level atom quadratically coupled to
two bosonic modes. This effect, named parity effect, consists in a high
sensitivity to the evenness or oddness of the total number of bosonic
excitations.Comment: Topical Review. To appear on J. Mod. Op
A criterion for entanglement in two two-level systems
We prove a necessary and sufficient condition for the occurrence of
entanglement in two two-level systems, simple enough to be of experimental
interest. Our results are illustrated in the context of a spin star system
analyzing the exact entanglement evolution of the central couple of spins.Comment: 4 pages, Submitted to Physical Review Letter
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