3,867 research outputs found
Entanglement versus mixedness for coupled qubits under a phase damping channel
Quantification of entanglement against mixing is given for a system of
coupled qubits under a phase damping channel. A family of pure initial joint
states is defined, ranging from pure separable states to maximally entangled
state. An ordering of entanglement measures is given for well defined initial
state amount of entanglement.Comment: 9 pages, 2 figures. Replaced with final published versio
Proper Motion of H2O Masers in IRAS 20050+2720 MMS1: An AU Scale Jet Associated with An Intermediate-Mass Class 0 Source
We conducted a 4 epoch 3 month VLBA proper motion study of HO masers
toward an intermediate-mass class 0 source IRAS 20050+2720 MMS1 (d=700 pc).
From milli-arcsecond (mas) resolution VLBA images, we found two groups of H2O
maser spots at the center of the submillimeter core of MMS1. One group consists
of more than intense maser spots; the other group consisting of
several weaker maser spots is located at 18 AU south-west of the intense group.
Distribution of the maser spots in the intense group shows an arc-shaped
structure which includes the maser spots that showed a clear velocity gradient.
The spatial and velocity structures of the maser spots in the arc-shape did not
significantly change through the 4 epochs. Furthermore, we found a relative
proper motion between the two groups. Their projected separation increased by
1.13+/-0.11 mas over the 4 epochs along a line connecting them. The spatial and
velocity structures of the intense group and the relative proper motions
strongly suggest that the maser emission is associated with a protostellar jet.
Comparing the observed LSR velocities with calculated radial velocities from a
simple biconical jet model, we conclude that the most of the maser emission are
likely to be associated with an accelerating biconical jet which has large
opening angle. The large opening angle of the jet traced by the masers would
support the hypothesis that poor jet collimation is an inherent property of
luminous (proto)stars.Comment: 14 pages, 10 figures, Fig.3 was downsized significantly. accepted for
publication in A&
183 GHz HO maser emission around the low-mass protostar Serpens SMM1
We report the first interferomteric detection of 183 GHz water emission in
the low-mass protostar Serpens SMM1 using the Submillimeter Array with a
resolution of 3 and rms of 7 Jy in a 3 km s bin. Due to the
small size and high brightnessof more than 240 Jy/beam, it appears to be maser
emission. In total three maser spots were detected out to 700 AU from
the central protostar, lying along the red-shifted outflow axis, outside the
circumstellar disk but within the envelope region as evidenced by the continuum
measurements. Two of the maser spots appear to be blue-shifted by about 1 to 2
km s. No extended or compact thermal emission from a passively heated
protostellar envelope was detected with a limit of 7 Jy (16 K), in agreement
with recent modelling efforts. We propose that the maser spots originate within
the cavity walls due to the interaction of the outflow jet with the surrounding
protostellar envelope. Hydrodynamical models predict that such regions can be
dense and warm enough to invert the 183 GHz water transition.Comment: Accepted for ApJ letters, 2 figure
First results from a VLBA proper motion survey of H2O masers in low-mass YSOs: the Serpens core and RNO15-FIR
This article reports first results of a long-term observational program aimed
to study the earliest evolution of jet/disk systems in low-mass YSOs by means
of VLBI observations of the 22.2 GHz water masers. We report here data for the
cluster of low-mass YSOs in the Serpens molecular core and for the single
object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the
Serpens cluster, the water maser emission comes from two small (< 5 AU in size)
clusters of features separated by ~25 AU, having line of sight velocities
strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of
the molecular cloud. The two maser clusters are oriented on the sky along a
direction that is approximately perpendicular to the axis of the radio
continuum jet observed with the VLA towards SMM1. The spatial and velocity
distribution of the maser features lead us to favor the interpretation that the
maser emission is excited by interaction of the receding lobe of the jet with
dense gas in the accretion disk surrounding the YSO in SMM1. Towards
RNO~15-FIR, the few detected maser features have both positions and (absolute)
velocities aligned along a direction that is parallel to the axis of the
molecular outflow observed on much larger angular scales. In this case the
maser emission likely emerges from dense, shocked molecular clumps displaced
along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1
is more massive than the one in RNO~15-FIR. We discuss the case where a high
mass ejection rate can generate jets sufficiently powerful to sweep away from
their course the densest portions of circumstellar gas. In this case, the
excitation conditions for water masers might preferably occur at the interface
between the jet and the accretion disk, rather than along the jet axis.Comment: 18 pages (postscript format); 9 figures; to be published into
Astronomy & Astrophysics, Main Journa
Semiclassical limit of the entanglement in closed pure systems
We discuss the semiclassical limit of the entanglement for the class of
closed pure systems. By means of analytical and numerical calculations we
obtain two main results: (i) the short-time entanglement does not depend on
Planck's constant and (ii) the long-time entanglement increases as more
semiclassical regimes are attained. On one hand, this result is in contrast
with the idea that the entanglement should be destroyed when the macroscopic
limit is reached. On the other hand, it emphasizes the role played by
decoherence in the process of emergence of the classical world. We also found
that, for Gaussian initial states, the entanglement dynamics may be described
by an entirely classical entropy in the semiclassical limit.Comment: 8 pages, 2 figures (accepted for publication in Phys. Rev. A
Non-Gaussian two-mode squeezing and continuous variable entanglement of linearly and circularly polarized light beams interacting with cold atoms
We investigate how entangled coherent states and superpositions of low
intensity coherent states of non-Gaussian nature can be generated via
non-resonant interaction between either two linearly or circularly polarized
field modes and an ensemble of X-like four-level atoms placed in an optical
cavity. We compare our results to recent experimental observations and argue
that the non-Gaussian structure of the field states may be present in those
systems.Comment: 10 pages, 7 figures, replaced with final published versio
Lymphocyte traffic and graft-versus-host disease after fully allogeneic small bowel transplantation
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
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