2,096 research outputs found
The extremely collimated bipolar H_2O jet from the NGC 1333-IRAS 4B protostar
We have performed observations of water maser emission towards a sample of
low-mass protostars, in order to investigate the properties of jets associated
with the earliest stages of star formation and their interaction with the
surrounding medium. The main aim is to measure the absolute positions and
proper motions of the H_2O spots in order to investigate the kinematics of the
region from where the jet is launched. We imaged the protostars in the nearby
region NGC 1333-IRAS 4 in the water maser line at 22.2 GHz by using the VLBA in
phase-reference mode at the milliarcsecond scale over four epochs, spaced by
one month to measure proper motions. Two protostars (A2 and B) were detected in
a highly variable H_2O maser emission, with an active phase shorter than four
weeks. The H_2O maps allow us to trace the fast jet driven by the B protostar:
we observed both the red- and blue-shifted lobes very close to the protostar,
=< 35 AU, moving away with projected velocities of ~10-50 km/s. The comparison
with the molecular outflow observed at larger scale suggests a jet precession
with a 18'/yr rate. By measuring the positional spread of the H_2O spots we
estimate a jet width of ~2 AU at a distance of ~12 AU from the driving
protostar.Comment: 9 pages, 8 figures, A&A accepte
Single-ion anisotropy in Haldane chains and form factor of the O(3) nonlinear sigma model
We consider spin-1 Haldane chains with single-ion anisotropy, which exists in
known Haldane chain materials. We develop a perturbation theory in terms of
anisotropy, where magnon-magnon interaction is important even in the low
temperature limit. The exact two-particle form factor in the O(3) nonlinear
sigma model leads to quantitative predictions on several dynamical properties
including dynamical structure factor and electron spin resonance frequency
shift. These agree very well with numerical results, and with experimental data
on the Haldane chain material Ni(CHN)N(PF)
Is Karenia a synonym of Asterodinium-Brachidinium (Gymnodiniales, Dinophyceae)?
From material collected in open waters of the NW and Equatorial Pacific Ocean the detailed morphology of brachidiniaceans based on two specimens of Asterodinium gracile is reported for the first time. SEM observations showed that the straight apical groove, the
morphological characters and orientation of the cell body were similar to those described for species of Karenia. Brachidinium and Asterodinium showed high morphological variability in the length of the extensions and intermediate specimens with Karenia. Karenia-like cells that strongly resemble Brachidinium and Asterodinium but lacking the extensions co-occurred with the typical specimens. The life cycle and morphology of Karenia papilionacea should be investigated under natural conditions because of the strong similarity
with the brachidiniaceans
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
Kerr nonlinearities and nonclassical states with superconducting qubits and nanomechanical resonators
We propose the use of a superconducting charge qubit capacitively coupled to
two resonant nanomechanical resonators to generate Yurke-Stoler states, i.e.
quantum superpositions of pairs of distinguishable coherent states 180
out of phase with each other. This is achieved by effectively implementing Kerr
nonlinearities induced through application of a strong external driving field
in one of the resonators. A simple study of the effect of dissipation on our
scheme is also presented, and lower bounds of fidelity and purity of the
generated state are calculated. Our procedure to implement a Kerr nonlinearity
in this system may be used for high precision measurements in nanomechanical
resonators.Comment: 5 pages, 2 figures, fixed typo
Global entangling properties of the coupled kicked tops
We study global entangling properties of the system of coupled kicked tops
testing various hypotheses and predictions concerning entanglement in quantum
chaotic systems. In order to analyze the averaged initial entanglement
production rate and the averaged asymptotic entanglement different ensembles of
initial product states are evolved. Two different ensembles with natural
probability distribution are considered: product states of independent
spin-coherent states and product states of arbitrary states. It appears that
the choice of either of these ensembles results in significantly different
averaged entanglement behavior. We investigate also a relation between the
averaged asymptotic entanglement and the mean entanglement of the eigenvectors
of an evolution operator. Lower bound on the averaged asymptotic entanglement
is derived, expressed in terms of the eigenvector entanglement.Comment: 11 pages, 7 figures, RevTe
Entanglement in the dispersive interaction of trapped ions with a quantized field
The mode-mode entanglement between trapped ions and cavity fields is
investigated in the dispersive regime. We show how a simple initial preparation
of Gaussian coherent states and a postselection may be used to generate
motional non-local mesoscopic states (NLMS) involving ions in different traps.
We also present a study of the entanglement induced by dynamical Stark-shifts
considering a cluster of N-trapped ions. In this case, all entanglement is due
to the dependence of the Stark-shifts on the ions' state of motion manifested
as a cross-Kerr interaction between each ion and the field.Comment: 10 pages, 5 figures, corrected typo
Unconditional Bell-type state generation for spatially separate trapped ions
We propose a scheme for generation of maximally entangled states involving
internal electronic degrees of freedom of two distant trapped ions, each of
them located in a cavity. This is achieved by using a single flying atom to
distribute entanglement. For certain specific interaction times, the proposed
scheme leads to the non-probabilistic generation of a perfect Bell-type state.
At the end of the protocol, the flying atom completely disentangles from the
rest of the system, leaving both ions in a Bell-type state. Moreover, the
scheme is insensitive to the cavity field state and cavity losses. We also
address the situation in which dephasing and dissipation must be taken into
account for the flying atom on its way from one cavity to the other, and
discuss the applicability of the resulting noisy channel for performing quantum
teleportation.Comment: 5 pages, 1 figure, detailed comments on the practical implementation
of the scheme is added to replaced version, minor typos fixed, added
references with comment
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