1,804 research outputs found
Item weighted Kemeny distance for preference data
Preference data represent a particular type of ranking data where a group of people gives their preferences over a set of alternatives. The traditional metrics between rankings don’t take into account that the importance of elements can be not uniform. In this paper the item weighted Kemeny distance is introduced and its properties demonstrated
Approximate reversibility in the context of entropy gain, information gain, and complete positivity
There are several inequalities in physics which limit how well we can process
physical systems to achieve some intended goal, including the second law of
thermodynamics, entropy bounds in quantum information theory, and the
uncertainty principle of quantum mechanics. Recent results provide physically
meaningful enhancements of these limiting statements, determining how well one
can attempt to reverse an irreversible process. In this paper, we apply and
extend these results to give strong enhancements to several entropy
inequalities, having to do with entropy gain, information gain, entropic
disturbance, and complete positivity of open quantum systems dynamics. Our
first result is a remainder term for the entropy gain of a quantum channel.
This result implies that a small increase in entropy under the action of a
subunital channel is a witness to the fact that the channel's adjoint can be
used as a recovery map to undo the action of the original channel. Our second
result regards the information gain of a quantum measurement, both without and
with quantum side information. We find here that a small information gain
implies that it is possible to undo the action of the original measurement if
it is efficient. The result also has operational ramifications for the
information-theoretic tasks known as measurement compression without and with
quantum side information. Our third result shows that the loss of Holevo
information caused by the action of a noisy channel on an input ensemble of
quantum states is small if and only if the noise can be approximately corrected
on average. We finally establish that the reduced dynamics of a
system-environment interaction are approximately completely positive and
trace-preserving if and only if the data processing inequality holds
approximately.Comment: v3: 12 pages, accepted for publication in Physical Review
The non-justiciability of third-party claims before UN internal dispute settlement mechanisms : The ‘politicization’ of (financially) burdensome questions
Very Prolonged Treatment with Albendazole of a Case of Disseminated Abdominal Cystic Echinococcosis
Cystic echinococcosis is a zoonosis caused by the ingestion of food or water contaminated by Echinococcus eggs. E. granulosus is the most common causative agent of cystic echinococcosis that still has a relevant incidence in Italy, especially on the islands of Sicily and Sardinia. We report the case of a 64-year-old man with disseminated abdominal cystic echinococcosis (liver, spleen, peritoneum). The patient was asymptomatic and non-eligible for surgical treatment. Treatment with albendazole 400 mg/twice daily was started in 2012 for 15 cycles (each cycle consisted of three 28-day treatments at 14-day intervals) over 10 years for a total of 1260 days of treatment. Serum anti-Echinococcus antibody titers and imaging (echography, TC) were evaluated to monitor the evolution of the disease. Imaging techniques documented the regression of all cyst lesions, but it was less evident for the peritoneal localizations that still are in follow-up. In this case, the prolonged treatment with albendazole was effective, safe and free of side effects. Until today, the patient displays a good clinical condition
A measure of tripartite entanglement in bosonic and fermionic systems
We describe an efficient theoretical criterion suitable for the evaluation of
the tripartite entanglement of any mixed three-boson or -fermion state, based
on the notion of the entanglement of particles for bipartite systems of
identical particles. Our approach allows one to quantify the accessible amount
of quantum correlations in the systems without any violation of the local
particle number superselection rule. A generalization of the tripartite
negativity is here applied to some correlated systems including the
continuous-time quantum walks of identical particles (both for bosons and
fermions) and compared with other criteria recently proposed in the literature.
Our results show the dependence of the entanglement dynamics upon the quantum
statistics: the bosonic bunching results into a low amount of quantum
correlations while Fermi-Dirac statistics allows for higher values of the
entanglement.Comment: 19 pages, 3 figure
Towards a unified approach to information-disturbance tradeoffs in quantum measurements
We show that the global balance of information dynamics for general quantum
measurements given in [F. Buscemi, M. Hayashi, and M. Horodecki, Phys.Rev.Lett.
100, 210504 (2008)] makes it possible to unify various and generally
inequivalent approaches adopted in order to derive information-disturbance
tradeoffs in quantum theory. We focus in particular on those tradeoffs,
constituting the vast majority of the literature on the subject, where
disturbance is defined either in terms of average output fidelity or of
entanglement fidelity
Dynamics of quantum correlations in colored environments
We address the dynamics of entanglement and quantum discord for two non
interacting qubits initially prepared in a maximally entangled state and then
subjected to a classical colored noise, i.e. coupled with an external
environment characterized by a noise spectrum of the form . More
specifically, we address systems where the Gaussian approximation fails, i.e.
the sole knowledge of the spectrum is not enough to determine the dynamics of
quantum correlations. We thus investigate the dynamics for two different
configurations of the environment: in the first case the noise spectrum is due
to the interaction of each qubit with a single bistable fluctuator with an
undetermined switching rate, whereas in the second case we consider a
collection of classical fluctuators with fixed switching rates. In both cases
we found analytical expressions for the time dependence of entanglement and
quantum discord, which may be also extended to a collection of flcutuators with
random switching rates. The environmental noise is introduced by means of
stochastic time-dependent terms in the Hamiltonian and this allows us to
describe the effects of both separate and common environments. We show that the
non-Gaussian character of the noise may lead to significant effects, e.g.
environments with the same power spectrum, but different configurations, give
raise to opposite behavior for the quantum correlations. In particular,
depending on the characteristics of the environmental noise considered, both
entanglement and discord display either a monotonic decay or the phenomena of
sudden death and revivals. Our results show that the microscopic structure of
environment, besides its noise spectrum, is relevant for the dynamics of
quantum correlations, and may be a valid starting point for the engineering of
non-Gaussian colored environments.Comment: 8 pages, 3 figure
Physical realizations of quantum operations
Quantum operations (QO) describe any state change allowed in quantum
mechanics, such as the evolution of an open system or the state change due to a
measurement. We address the problem of which unitary transformations and which
observables can be used to achieve a QO with generally different input and
output Hilbert spaces. We classify all unitary extensions of a QO, and give
explicit realizations in terms of free-evolution direct-sum dilations and
interacting tensor-product dilations. In terms of Hilbert space dimensionality
the free-evolution dilations minimize the physical resources needed to realize
the QO, and for this case we provide bounds for the dimension of the ancilla
space versus the rank of the QO. The interacting dilations, on the other hand,
correspond to the customary ancilla-system interaction realization, and for
these we derive a majorization relation which selects the allowed unitary
interactions between system and ancilla.Comment: 8 pages, no figures. Accepted for publication on Phys. Rev.
Noise and disturbance in quantum measurements: an information-theoretic approach
We introduce information-theoretic definitions for noise and disturbance in
quantum measurements and prove a state-independent noise-disturbance tradeoff
relation that these quantities have to satisfy in any conceivable setup.
Contrary to previous approaches, the information-theoretic quantities we define
are invariant under relabelling of outcomes, and allow for the possibility of
using quantum or classical operations to `correct' for the disturbance. We also
show how our bound implies strong tradeoff relations for mean square
deviations.Comment: v3: to appear on PRL (some issues fixed, supplemental material
expanded). v2: replaced with submitted version; 5 two-column pages + 6
one-column pages + 3 figures; one issue corrected and few references added.
v1: 17 pages, 3 figure
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