115,105 research outputs found
Multipartite entanglement in three-mode Gaussian states of continuous variable systems: Quantification, sharing structure and decoherence
We present a complete analysis of multipartite entanglement of three-mode
Gaussian states of continuous variable systems. We derive standard forms which
characterize the covariance matrix of pure and mixed three-mode Gaussian states
up to local unitary operations, showing that the local entropies of pure
Gaussian states are bound to fulfill a relationship which is stricter than the
general Araki-Lieb inequality. Quantum correlations will be quantified by a
proper convex roof extension of the squared logarithmic negativity (the
contangle), satisfying a monogamy relation for multimode Gaussian states, whose
proof will be reviewed and elucidated. The residual contangle, emerging from
the monogamy inequality, is an entanglement monotone under Gaussian local
operations and classical communication and defines a measure of genuine
tripartite entanglement. We analytically determine the residual contangle for
arbitrary pure three-mode Gaussian states and study the distribution of quantum
correlations for such states. This will lead us to show that pure, symmetric
states allow for a promiscuous entanglement sharing, having both maximum
tripartite residual entanglement and maximum couplewise entanglement between
any pair of modes. We thus name these states GHZ/ states of continuous
variable systems because they are simultaneous continuous-variable counterparts
of both the GHZ and the states of three qubits. We finally consider the
action of decoherence on tripartite entangled Gaussian states, studying the
decay of the residual contangle. The GHZ/ states are shown to be maximally
robust under both losses and thermal noise.Comment: 20 pages, 5 figures. (v2) References updated, published versio
Determination of continuous variable entanglement by purity measurements
We classify the entanglement of two--mode Gaussian states according to their
degree of total and partial mixedness. We derive exact bounds that determine
maximally and minimally entangled states for fixed global and marginal
purities. This characterization allows for an experimentally reliable estimate
of continuous variable entanglement based on measurements of purity.Comment: 4 pages, 3 EPS figures. Final versio
Observing gravitational lensing effects by Sgr A* with GRAVITY
The massive black hole at the Galactic center Sgr A* is surrounded by a
cluster of stars orbiting around it. Light from these stars is bent by the
gravitational field of the black hole, giving rise to several phenomena:
astrometric displacement of the primary image, the creation of a secondary
image that may shift the centroid of Sgr A*, magnification effects on both
images. The near-to-come second generation VLTI instrument GRAVITY will perform
observations in the Near Infrared of the Galactic Center at unprecedented
resolution, opening the possibility of observing such effects. Here we
investigate the observability limits for GRAVITY of gravitational lensing
effects on the S-stars in the parameter space [DLS,gamma,K], where DLS is the
distance between the lens and the source, gamma is the alignment angle of the
source, and K is the source apparent magnitude in the K-band. The easiest
effect to be observed in the next years is the astrometric displacement of
primary images. In particular the shift of the star S17 from its Keplerian
orbit will be detected as soon as GRAVITY becomes operative. For exceptional
configurations it will be possible to detect effects related to the spin of the
black hole or Post-Newtonian orders in the deflection.Comment: 29 pages, 9 figures, in press on Ap
Phosphido pincer complexes of platinum: synthesis, structure and reactivity
A series of platinum(II) complexes supported by the tridentate bis(phosphine)phosphido ligand bis(2-diisopropylphosphinophenyl)phosphide) [iPr–PPP] have been synthesized and characterized (1–4). X-Ray structural studies of [iPr–PPP]PtCl (1) and [iPr–PPP]PtCH3 (3) complexes show meridional [iPr–PPP] ligands around approximately square-planar platinum centers. Structural data and NMR analysis highlight a strong trans influence for the phosphido phosphorous donor, comparable to that of the anionic aryl carbon of the classic PCP pincer complexes. A series of thermally stable [PPP]Pt(IV) compounds, including [PPP]Pt(CH_3)_2X [X = I (5) and SbF_6 (6)], were also synthesized. The study of the binding affinity of SO_2 and NO to complex 1 has also been addressed
Shock waves in one-dimensional Heisenberg ferromagnets
We use SU(2) coherent state path integral formulation with the stationary
phase approximation to investigate, both analytically and numerically, the
existence of shock waves in the one- dimensional Heisenberg ferromagnets with
anisotropic exchange interaction. As a result we show the existence of shock
waves of two types,"bright" and "dark", which can be interpreted as moving
magnetic domains.Comment: 10 pages, with 3 ps figure
Understanding flavor mixing in Quantum Field Theory
We report on recent results showing that a rich non-perturbative vacuum
structure is associated with flavor mixing in Quantum Field Theory.
We treat explicitly the case of mixing among three generations of Dirac
fermions.
Exact oscillation formulas are presented exhibiting new features with respect
to the usual ones. CP and T violation are also discussed.Comment: 9 pages. Presented at the "International Conference on Flavor
Physics", Zhang-Jia-Jie, China, May 31 - June 6 200
Adiabatic Compression of Soliton Matter Waves
The evolution of atomic solitary waves in Bose-Einstein condensate (BEC)
under adiabatic changes of the atomic scattering length is investigated. The
variations of amplitude, width, and velocity of soliton are found for both
spatial and time adiabatic variations. The possibility to use these variations
to compress solitons up to very high local matter densities is shown both in
absence and in presence of a parabolic confining potential.Comment: to appear in J.Phys.
Phase rigidity breaking in open Aharonov-Bohm ring coupled to a cantilever
The conductance and the transmittance phase shifts of a two-terminal
Aharonov-Bohm (AB) ring are analyzed in the presence of mechanical
displacements due to coupling to an external can- tilever. We show that phase
rigidity is broken, even in the linear response regime, by means of inelastic
scattering due to phonons. Our device provides a way of observing continuous
variation of the transmission phase through a two-terminal
nano-electro-mechanical system (NEMS). We also propose measurements of phase
shifts as a way to determine the strength of the electron-phonon coupling in
NEMS.Comment: 7 pages, 8 figure
Matter-wave 2D solitons in crossed linear and nonlinear optical lattices
It is demonstrated the existence of multidimensional matter-wave solitons in
a crossed optical lattice (OL) with linear OL in the direction and
nonlinear OL (NOL) in the direction, where the NOL can be generated by a
periodic spatial modulation of the scattering length using an optically induced
Feshbach resonance. In particular, we show that such crossed linear and
nonlinear OL allows to stabilize two-dimensional (2D) solitons against decay or
collapse for both attractive and repulsive interactions. The solutions for the
soliton stability are investigated analytically, by using a multi-Gaussian
variational approach (VA), with the Vakhitov-Kolokolov (VK) necessary criterion
for stability; and numerically, by using the relaxation method and direct
numerical time integrations of the Gross-Pitaevskii equation (GPE). Very good
agreement of the results corresponding to both treatments is observed.Comment: 8 pages (two-column format), with 16 eps-files of 4 figure
How to deal with the arrow of time in quantum field theory
The formalism of Quantum Mechanics is based by definition on conserving
probabilities and thus there is no room for the description of dissipative
systems in Quantum Mechanics. The treatment of time-irreversible evolution (the
arrow of time) is therefore ruled out by definition in Quantum Mechanics. In
Quantum Field Theory it is, however, possible to describe time-irreversible
evolution by resorting to the existence of infinitely many unitarily
inequivalent representations of the canonical commutation relations (ccr). In
this paper I review such a result by discussing the canonical quantization of
the damped harmonic oscillator (dho), a prototype of dissipative systems. The
irreversibility of time evolution is expressed as tunneling among the unitarily
inequivalent representations. The exact action for the dho is derived in the
path integral formalism of the quantum Brownian motion developed by Schwinger
and by Feynman and Vernon. The doubling of the phase-space degrees of freedom
for dissipative systems is related to quantum noise effects. Finally, the role
of dissipation in the quantum model of the brain and the occurrence that the
cosmological arrow of time, the thermodynamical one and the biological one
point into the same direction are shortly mentioned.Comment: 16 pages, Latex, Talk delivered at the XXIV International Workshop on
Fundamental Problems of High Energy Physics and Field Theory, Protvino, June
2001 Proceeding available at http://dbserv.ihep.su/~pub
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