793 research outputs found
Private states, quantum data hiding and the swapping of perfect secrecy
We derive a formal connection between quantum data hiding and quantum
privacy, confirming the intuition behind the construction of bound entangled
states from which secret bits can be extracted. We present three main results.
First, we show how to simplify the class of private states and related states
via reversible local operation and one-way communication. Second, we obtain a
bound on the one-way distillable entanglement of private states in terms of
restricted relative entropy measures, which is tight in many cases and shows
that protocols for one-way distillation of key out of states with low
distillable entanglement lead to the distillation of data hiding states. Third,
we consider the problem of extending the distance of quantum key distribution
with help of intermediate stations. In analogy to the quantum repeater, this
paradigm has been called the quantum key repeater. We show that when extending
private states with one-way communication, the resulting rate is bounded by the
one-way distillable entanglement. In order to swap perfect secrecy it is thus
essentially optimal to use entanglement swapping.Comment: v3 published version, some details of the main proofs have been moved
to the appendix, 21 pages. v2 claims changed from LOCC to one-way LOCC in the
process of correcting a mistake found in v1 (in proof of Lemma 3). v1: 15
pages, 9 figure
First CO(17-16) emission line detected in a z > 6 quasar
We report the serendipitous detection of the CO(17-16) emission line toward
the quasar SDSSJ114816.64+525150.3 (J1148) at redshift z = 6.4 obtained with
the Plateau de Bure Interferometer. The CO(17-16) line is possibly contaminated
by OH+ emission, that may account for ~ 35 - 60% of the total flux observed.
Photo-Dissociation and X-ray Dominated Regions (PDRs and XDRs) models show that
PDRs alone cannot reproduce the high luminosity of the CO(17-16) line relative
to low-J CO transitions and that XDRs are required. By adopting a composite
PDR+XDR model we derive molecular cloud and radiation field properties in the
nuclear region of J1148. Our results show that highly excited CO lines
represent a sensitive and possibly unique tool to infer the presence of X-ray
faint or obscured supermassive black hole progenitors in high-z galaxies.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Lette
Applicazione dei laser scanner terrestri in campo agro-forestale e ambientale
Le tecniche di laser scanning terrestre suscitano un interesse sempre più crescente sia in campo ambientale sia in campo agro-forestale in quanto consentono un’acquisizione rapida e affidabile di nuvole di punti 3D in grado di rappresentare tridimensionalmente gli oggetti rilevati. In un lasso di tempo relativamente breve, tali tecniche hanno aperto la strada ad un ampio spettro di applicazioni in pieno campo. Al di là della misura interattiva di nuvole georeferenziate di punti, le tecniche per il rilevamento automatizzato di oggetti, la determinazione delle loro caratteristiche geometriche e l’analisi della risposta del segnale laser rappresentano temi di ricerca prioritari. L’elevata qualità delle nuvole di punti 3D generate dai sistemi di laser scanning insieme alla possibilità di automatizzare le successive post-elaborazioni dei dati hanno esteso il potenziale applicativo dei laser scanner terrestri anche ai settori ambientali e agro-forestali. Questo contributo illustra innanzitutto lo stato dell’arte dei sistemi laser scanner terrestri dal punto di vista tecnologico e discute le diverse soluzioni tecnologiche e i diversi parametri di sistema in relazione alle possibili applicazioni in campo ambientale e forestale. Nella seconda parte saranno invece presentati alcuni casi di studio esplicativi delle potenzialità e delle limitazioni operative della tecnica di laser scanning terrestre in campo ambientale e agro-forestale.
Terrestrial laser scanning techniques find rapidly growing interest in both environmental and agro-forestry fields as efficient tools for fast and reliable 3D point data acquisition and 3D representation of the object viewed by the scanners. They have opened a wide range of application fields within a rather short period of time. Beyond interactive measurement in 3D point clouds, techniques for the automatic detection of objects, the determination of geometric parameters, and the analysis of the reflectance signal form high priority research issues. The high quality of 3D point clouds generated by laser scanners and the data process automation potential make terrestrial laser scanning also an interesting tool for environmental and agro-forestry applications. The paper will first review current laser scanner systems from a technological point of view and discuss different scanner technologies and system parameters regarding their suitability for environmental and agro-forestry applications. In the second part of the paper, results of case studies on potentials and limitations of terrestrial laser scanners in environmental and agro-forestry fields will be presented
X-ray spectroscopy of the z=6.4 quasar J1148+5251
We present the 78-ks Chandra observations of the quasar SDSS
J1148+5251. The source is clearly detected in the energy range 0.3-7 keV with
42 counts (with a significance ). The X-ray spectrum is
best-fitted by a power-law with photon index absorbed by a gas
column density of .
We measure an intrinsic luminosity at 2-10 keV and 10-40 keV equal to , comparable with luminous local and
intermediate-redshift quasar properties. Moreover, the X-ray to optical
power-law slope value () of J1148 is consistent
with the one found in quasars with similar rest-frame 2500 \AA ~luminosity
(\AA). Then we use Chandra data
to test a physically motivated model that computes the intrinsic X-ray flux
emitted by a quasar starting from the properties of the powering black hole and
assuming that X-ray emission is attenuated by intervening, metal-rich () molecular clouds distributed on kpc scales in the host
galaxy. Our analysis favors a black hole mass and a molecular hydrogen mass , in good agreement with estimates obtained from previous studies. We
finally discuss strengths and limits of our analysis.Comment: 9 pages, 3 figures, 1 table, MNRAS in pres
Random private quantum states
The study of properties of randomly chosen quantum states has in recent years
led to many insights into quantum entanglement. In this work, we study private
quantum states from this point of view. Private quantum states are bipartite
quantum states characterised by the property that carrying out simple local
measurements yields a secret bit. This feature is shared by the maximally
entangled pair of quantum bits, yet private quantum states are more general and
can in their most extreme form be almost bound entangled. In this work, we
study the entanglement properties of random private quantum states and show
that they are hardly distinguishable from separable states and thus have low
repeatable key, despite containing one bit of key. The technical tools we
develop are centred around the concept of locally restricted measurements and
include a new operator ordering, bounds on norms under tensoring with entangled
states and a continuity bound for a relative entropy measure.Comment: v3: published version. v2: 13+7 pages, 1 figure, corrected
statements. v1: 16+8 pages, no figure
GHG emissions inventory at urban scale: the Sassari case study
Within current initiatives dedicated to provide information on the status of greenhouse gases emissions, the town of Sassari represents a pilot site for estimating the net exchange of carbon dioxide (emissions and sinks) at municipal level in Sardinia (Italy). A spatial and temporal high resolution greenhouse gas emissions inventory for the urban area of Sassari is currently under construction in line with European and international standard protocols to establish a baseline for tracking emission trends. This paper presents the preliminary results of the development of a simplified local emissions inventory where estimates of the atmospheric emissions are collected and cataloged by type of greenhouse gases, productive activity and emissive source on annual basis
Deterministic Identification Over Multiple-Access Channels
Deterministic identification over K-input multiple-access channels with
average input cost constraints is considered. The capacity region for
deterministic identification is determined for an average-error criterion,
where arbitrarily large codes are achievable. For a maximal-error criterion,
upper and lower bounds on the capacity region are derived. The bounds coincide
if all average partial point-to-point channels are injective under the input
constraint, i.e. all inputs at one terminal are mapped to distinct output
distributions, if averaged over the inputs at all other terminals. The
achievability is proved by treating the MAC as an arbitrarily varying channel
with average state constraints. For injective average channels, the capacity
region is a hyperrectangle. The modulo-2 and modulo-3 binary adder MAC are
presented as examples of channels which are injective under suitable input
constraints. The binary multiplier MAC is presented as an example of a
non-injective channel, where the achievable identification rate region still
includes the Shannon capacity region.Comment: ISIT 2023 versio
Comparison of Quantum PUF models
Physical unclonable functions (PUFs) are hardware structures in a physical
system (e.g. semiconductor, crystals etc.) that are used to enable unique
identification of the semiconductor or to secure keys for cryptographic
processes. A PUF thus generates a noisy secret reproducible at runtime. This
secret can either be used to authenticate the chip, or it is available as a
cryptographic key after removing the noise. Latest advancements in the field of
quantum hardware, in some cases claiming to achieve quantum supremacy, highly
target the fragility of current RSA type classical cryptosystems. As a
solution, one would like to develop Quantum PUFs to mitigate such problem.
There are several approaches for this technology. In our work we compare these
different approaches and introduce the requirements for QTOKSim, a quantum
token based authentication simulator testing its performance on a multi-factor
authentication protocol
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