1,120 research outputs found
Detecting Gaussian entanglement via extractable work
We show how the presence of entanglement in a bipartite Gaussian state can be
detected by the amount of work extracted by a continuos variable Szilard-like
device, where the bipartite state serves as the working medium of the engine.
We provide an expression for the work extracted in such a process and
specialize it to the case of Gaussian states. The extractable work provides a
sufficient condition to witness entanglement in generic two-mode states,
becoming also necessary for squeezed thermal states. We extend the protocol to
tripartite Gaussian states, and show that the full structure of inseparability
classes cannot be discriminated based on the extractable work. This suggests
that bipartite entanglement is the fundamental resource underpinning work
extraction.Comment: 12 pages, 8 figure
Non-equilibrium readiness and accuracy of Gaussian Quantum Thermometers
The dimensionality of a thermometer is key in the design of quantum
thermometry schemes. In general, the phenomenology that is typical of
finite-dimensional quantum thermometry does not apply to infinite dimensional
ones. We analyse the dynamical and metrological features of non-equilibrium
Gaussian Quantum Thermometers: on one hand, we highlight how quantum
entanglement can enhance the readiness of composite Gaussian thermometers; on
the other hand, we show that non-equilibrium conditions do not guarantee the
best sensitivities in temperature estimation, thus suggesting the reassessment
of the working principles of quantum thermometry
Diffeological Symplectic Frobenius Reciprocity
In this note we prove that the symplectic Frobenius Reciprocity established
in the paper "Symplectic Induction, Prequantum Induction and Prequantum
Multiplicities" as a set bijection is indeed a diffeological diffeomorphism, as
conjectured by its authors Ratiu and Ziegler. The same holds in the prequantum
space context.Comment: 14 page
The Earth transiting the Sun as seen from Jupiter's moons: detection of an inverse Rossiter-McLaughlin effect produced by the Opposition Surge of the icy Europa
We report on a multi-wavelength observational campaign which followed the
Earth's transit on the Sun as seen from Jupiter on 5 Jan the 2014. Simultaneous
observations of Jupiter's moons Europa and Ganymede obtained with HARPS from La
Silla, Chile, and HARPS-N from La Palma, Canary Islands, were performed to
measure the Rossiter-McLaughlin effect due to the Earth's passage using the
same technique successfully adopted for the 2012 Venus Transit (Molaro et al
2013). The expected modulation in radial velocities was of about 20 cm/s but an
anomalous drift as large as 38 m/s, i.e. more than two orders of magnitude
higher and opposite in sign, was detected instead. The consistent behaviour of
the two spectrographs rules out instrumental origin of the radial velocity
drift and BiSON observations rule out the possible dependence on the Sun's
magnetic activity. We suggest that this anomaly is produced by the Opposition
Surge on Europa's icy surface, which amplifies the intensity of the solar
radiation from a portion of the solar surface centered around the crossing
Earth which can then be observed as a a sort of inverse Rossiter-McLaughling
effect. in fact, a simplified model of this effect can explain in detail most
features of the observed radial velocity anomalies, namely the extensions
before and after the transit, the small differences between the two
observatories and the presence of a secondary peak closer to Earth passage.
This phenomenon, observed here for the first time, should be observed every
time similar Earth alignments occur with rocky bodies without atmospheres. We
predict it should be observed again during the next conjunction of Earth and
Jupiter in 2026.Comment: 9 pages, 7 figure
Adaptive real time selection for quantum key distribution in lossy and turbulent free-space channels
The unconditional security in the creation of cryptographic keys obtained by quantum key distribution (QKD) protocols will induce a quantum leap in free-space communication privacy in the same way that we are beginning to realize secure optical fiber connections. However, free-space channels, in particular those with long links and the presence of atmospheric turbulence, are affected by losses, fluctuating transmissivity, and background light that impair the conditions for secure QKD. Here we introduce a method to contrast the atmospheric turbulence in QKD experiments. Our adaptive real time selection (ARTS) technique at the receiver is based on the selection of the intervals with higher channel transmissivity. We demonstrate, using data from the Canary Island 143-km free-space link, that conditions with unacceptable average quantum bit error rate which would prevent the generation of a secure key can be used once parsed according to the instantaneous scintillation using the ARTS technique
Agende Regionali: Piemonte
Entro il quadro generale del Rapporto dal Territorio nazionale, il capitolo affronta il tema dello stato del sistema di pianificazione urbanistica e territoriale nella Regione Piemonte
Phenomenological Implications of Supersymmetry Breaking by the Dilaton
We investigate the low energy properties of string vacua with spontaneously
broken supersymmetry by a dilaton -term. As a consequence of the
universal couplings of the dilaton, the supersymmetric mass spectrum is
determined in terms of only three independent parameters and more constrained
than in the minimal supersymmetric Standard Model. For a -term induced by
the \K\ potential the parameter space becomes two-dimensional; in the allowed
regions of this parameter space we find that most supersymmetric particles are
determined solely by the gluino mass. The Higgs is rather light and the
top-quark mass always lower than 180 GeV.Comment: 14 pages, (4 figures not included, available upon request),
CERN-TH.6856/93 (In the previous version of this article the gaugino masses
were given incorrectly. As a consequences the quantitative analysis of the
low energy spectrum changes.
Planetary formation in the Gamma-Cephei system
We numerically investigate under which conditions the planet detected at 2.1
AU of Gamma-Cephei could form through the core-accretion scenario despite the
perturbing presence of the highly eccentric companion star. We first show that
the initial stage of runaway accretion of kilometer-sized planetesimals is
possible within 2.5 AU from the central star only if large amounts of gas are
present. In this case, gaseous friction induces periastron alignment of the
orbits which reduces the otherwise high mutual impact velocities due to the
companion's secular perturbations. The following stage of mutual accretion of
large embryos is also modeled. According to our simulations, the giant impacts
among the embryos always lead to a core of 10 Mearth within 10 Myr, the average
lifetime of gaseous discs. However, the core always ends up within 1.5 AU from
the central star. Either the core grows more quickly in the inner region of the
disc, or it migrates inside by scattering the residual embryosComment: 8 pages, 12 figures to appear in Astronomy and Astrophysics (accepted
08/06/2004
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