4,850 research outputs found
Decoherence induced by a phase-damping reservoir
A phase damping reservoir composed by -bosons coupled to a system of
interest through a cross-Kerr interaction is proposed and its effects on
quantum superpo sitions are investigated. By means of analytical calculations
we show that: i-) the reservoir induces a Gaussian decay of quantum coherences,
and ii-) the inher ent incommensurate character of the spectral distribution
yields irreversibility . A state-independent decoherence time and a master
equation are both derived an alytically. These results, which have been
extended for the thermodynamic limit, show that nondissipative decoherence can
be suitably contemplated within the EI D approach. Finally, it is shown that
the same mechanism yielding decoherence ar e also responsible for inducing
dynamical disentanglement.Comment: 8 pages, 3 figure
Enlightening the dynamical evolution of Galactic open clusters: an approach using Gaia DR3 and analytical descriptions
Most stars in our Galaxy form in stellar aggregates, which can become
long-lived structures called open clusters (OCs). Along their dynamical
evolution, their gradual depletion leave some imprints on their structure. In
this work, we employed astrometric, photometric and spectroscopic data from the
\textit{Gaia} DR3 catalogue to uniformly characterize a sample of 60 OCs.
Structural parameters (tidal, core and half-light radii, respectively, ,
and ), age, mass (), distance, reddening, besides
Jacobi radius () and half-light relaxation time (), are derived
from radial density profiles and astrometrically decontaminated
colour-magnitude diagrams. Ages and Galactocentric distances () range from
7.2log(yr)9.8 and
6(kpc)12. Analytical expressions derived from
-body simulations, taken from the literature, are also employed to estimate
the OC initial mass () and mass loss due to exclusively
dynamical effects. Both and the tidal filling ratio, , tend to
decrease with the dynamical age (=), indicating the shrinking of the
OCs' internal structure as consequence of internal dynamical relaxation. This
dependence seems differentially affected by the external tidal field, since OCs
at smaller tend to be dynamically older and have smaller
ratios. In this sense, for
kpc, the ratio presents a slight positive correlation
with . Beyond this limit, there is a dichotomy in which more massive OCs
tend to be more compact and therefore less subject to tidal stripping in
comparison to those less massive and looser OCs at similar . Besides, the
ratio also tends to correlate positively with .Comment: 21 pages, 15 figures. Accepted for publication in MNRA
Investigating dynamical properties of evolved Galactic open clusters
The stellar content of Galactic open clusters is gradually depleted during
their evolution as a result of internal relaxation and external interactions.
The final residues of the evolution of open clusters are called open cluster
remnants, barely distinguishable from the field. We aimed to characterise and
compare the dynamical states of a set of 16 such objects. The sample also
includes 7 objects that are catalogued as dynamically evolved open clusters. We
used photometric data from the 2MASS, astrometric data from the GAIA DR2 and a
decontamination algorithm that was applied to the three-dimensional astrometric
space of proper motions and parallaxes for stars in the objects' areas. The
luminosity and mass functions and total masses for most open cluster remnants
are derived here for the first time. Our analysis used predictions of N-body
simulations to estimate the initial number of stars of the remnants from their
dissolution timescales. The investigated open cluster remnants present masses
and velocity dispersions within well-defined ranges: M between ~10-40M_Sun and
sigma_v between ~1-7km/s. Some objects in the remnant sample have a limiting
radius R_lim<~2pc, which means that they are more compact than the investigated
open clusters; other remnants have R_lim between ~2-7pc, which is comparable to
the open clusters. We suggest that the open cluster NGC2180 is entering a
remnant evolutionary stage. In general, our clusters show signals of depletion
of low-mass stars. This confirms their dynamically evolved states. We conclude
that the open cluster remnants we studied are in fact remnants of initially
very populous open clusters (No~10^3-10^4 stars). The outcome of the long-term
evolution is to bring the final residues of the open clusters to dynamical
states that are similar to each other, thus masking out the memory of the
initial formation conditions of star clusters.Comment: Accepted for publication in A&
The quantum theory of measurement within dynamical reduction models
We analyze in mathematical detail, within the framework of the QMUPL model of
spontaneous wave function collapse, the von Neumann measurement scheme for the
measurement of a 1/2 spin particle. We prove that, according to the equation of
the model: i) throughout the whole measurement process, the pointer of the
measuring device is always perfectly well localized in space; ii) the
probabilities for the possible outcomes are distributed in agreement with the
Born probability rule; iii) at the end of the measurement the state of the
microscopic system has collapsed to the eigenstate corresponding to the
measured eigenvalue. This analysis shows rigorously how dynamical reduction
models provide a consistent solution to the measurement problem of quantum
mechanics.Comment: 24 pages, RevTeX. Minor changes mad
On the Electromagnetic Properties of Matter in Collapse Models
We discuss the electromagnetic properties of both a charged free particle,
and a charged particle bounded by an harmonic potential, within collapse
models. By choosing a particularly simple, yet physically relevant, collapse
model, and under only the dipole approximation, we are able to solve the
equation of motion exactly. In this way, both the finite time and large time
behavior can be analyzed accurately. We discovered new features, which did not
appear in previous works on the same subject. Since, so far, the spontaneous
photon emission process places the strongest upper bounds on the collapse
parameters, our results call for a further analysis of this process for those
atomic systems which can be employed in experimental tests of collapse models,
as well as of quantum mechanics.Comment: 17 pages, LaTeX, updated version with minor change
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