10,151 research outputs found
IGR J19294+1816: a new Be-X ray binary revealed through infrared spectroscopy
The aim of this work is to characterize the counterpart to the INTEGRAL High
Mass X-ray Binary candidate IGR J19294+1816 so as to establish its true nature.
We obtained H band spectra of the selected counterpart acquired with the NICS
instrument mounted on the Telescopio Nazionale Galileo (TNG) 3.5-m telescope
which represents the first infrared spectrum ever taken of this source. We
complement the spectral analysis with infrared photometry from UKIDSS, 2MASS,
WISE and NEOWISE databases. We classify the mass donor as a Be star.
Subsequently, we compute its distance by properly taking into account the
contamination produced by the circumstellar envelope. The findings indicate
that IGR J19294+1816 is a transient source with a B1Ve donor at a distance of
kpc, and luminosities of the order of erg s,
displaying the typical behaviour of a Be X-ray binary.Comment: 8 pages, 6 figures, accepted to be published in MNRA
Fluctons
From the perspective of topological field theory we explore the physics
beyond instantons. We propose the fluctons as nonperturbative topological
fluctuations of vacuum, from which the self-dual domain of instantons is
attained as a particular case. Invoking the Atiyah-Singer index theorem, we
determine the dimension of the corresponding flucton moduli space, which gives
the number of degrees of freedom of the fluctons. An important consequence of
these results is that the topological phases of vacuum in non-Abelian gauge
theories are not necessarily associated with self-dual fields, but only with
smooth fields. Fluctons in different scenarios are considered, the basic
aspects of the quantum mechanical amplitude for fluctons are discussed, and the
case of gravity is discussed briefly
Singular Lagrangian Systems on Jet Bundles
The jet bundle description of time-dependent mechanics is revisited. The
constraint algorithm for singular Lagrangians is discussed and an exhaustive
description of the constraint functions is given. By means of auxiliary
connections we give a basis of constraint functions in the Lagrangian and
Hamiltonian sides. An additional description of constraints is also given
considering at the same time compatibility, stability and second-order
condition problems. Finally, a classification of the constraints in first and
second class is obtained using a cosymplectic geometry setting. Using the
second class constraints, a Dirac bracket is introduced, extending the
well-known construction by Dirac.Comment: 65 pages. LaTeX fil
Inductive Entanglement Classification of Four Qubits under SLOCC
Using an inductive approach to classify multipartite entangled states under
stochastic local operations and classical communication introduced recently by
the authors [Phys. Rev. A 74, 052336 (2006)], we give the complete
classification of four-qubit entangled pure states. Apart from the expected
degenerate classes, we show that there exist eight inequivalent ways to
entangle four qubits. In this respect, permutation symmetry is taken into
account and states with a structure differing only by parameters inside a
continuous set are considered to belong to the same class.Comment: 11 pages and no figures. Accepted in PR
Quantum Estimation Methods for Quantum Illumination
Quantum illumination consists in shining quantum light on a target region
immersed in a bright thermal bath, with the aim of detecting the presence of a
possible low-reflective object. If the signal is entangled with the receiver,
then a suitable choice of the measurement offers a gain with respect to the
optimal classical protocol employing coherent states. Here, we tackle this
detection problem by using quantum estimation techniques to measure the
reflectivity parameter of the object, showing an enhancement in the
signal-to-noise ratio up to 3 dB with respect to the classical case when
implementing only local measurements. Our approach employs the quantum Fisher
information to provide an upper bound for the error probability, supplies the
concrete estimator saturating the bound, and extends the quantum illumination
protocol to non-Gaussian states. As an example, we show how Schrodinger's cat
states may be used for quantum illumination.Comment: Published versio
Reaching the boundary between stellar kinematic groups and very wide binaries. III. Sixteen new stars and eight new wide systems in the beta Pictoris moving group
Aims. We look for common proper motion companions to stars of the nearby
young beta Pictoris moving group. Methods. First, we compiled a list of 185
beta Pictoris members and candidate members from 35 representative works. Next,
we used the Aladin and STILTS virtual observatory tools, and the PPMXL proper
motion and Washington Double Star catalogues to look for companion candidates.
The resulting potential companions were subjects of a dedicated
astro-photometric follow-up using public data from all-sky surveys. After
discarding 67 sources by proper motion and 31 by colour-magnitude diagrams, we
obtained a final list of 36 common proper motion systems. The binding energy of
two of them is perhaps too small to be considered physically bound. Results. Of
the 36 pairs and multiple systems, eight are new, 16 have only one stellar
component previously classified as a beta Pictoris member, and three have
secondaries at or below the hydrogen-burning limit. Sixteen stars are reported
here for the first time as moving group members. The unexpected large number of
high-order multiple systems, 12 triples and two quadruples among 36 systems,
may suggest a biased list of members towards close binaries or an increment of
the high-order-multiple fraction for very wide systems.Comment: A&A in pres
Algorithmic quantum simulation of memory effects
We propose a method for the algorithmic quantum simulation of memory effects
described by integrodifferential evolution equations. It consists in the
systematic use of perturbation theory techniques and a Markovian quantum
simulator. Our method aims to efficiently simulate both completely positive and
nonpositive dynamics without the requirement of engineering non-Markovian
environments. Finally, we find that small error bounds can be reached with
polynomially scaling resources, evaluated as the time required for the
simulation
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