138 research outputs found
Unified entropic measures of quantum correlations induced by local measurements
We introduce quantum correlations measures based on the minimal change in
unified entropies induced by local rank-one projective measurements, divided by
a factor that depends on the generalized purity of the system in the case of
non-additive entropies. In this way, we overcome the issue of the artificial
increasing of the value of quantum correlations measures based on non-additive
entropies when an uncorrelated ancilla is appended to the system without
changing the computability of our entropic correlations measures with respect
to the previous ones. Moreover, we recover as limiting cases the quantum
correlations measures based on von Neumann and R\'enyi entropies (i.e.,
additive entropies), for which the adjustment factor becomes trivial. In
addition, we distinguish between total and semiquantum correlations and obtain
some relations between them. Finally, we obtain analytical expressions of the
entropic correlations measures for typical quantum bipartite systems.Comment: 10 pages, 1 figur
A family of generalized quantum entropies: definition and properties
We present a quantum version of the generalized -entropies,
introduced by Salicr\'u \textit{et al.} for the study of classical probability
distributions. We establish their basic properties, and show that already known
quantum entropies such as von Neumann, and quantum versions of R\'enyi,
Tsallis, and unified entropies, constitute particular classes of the present
general quantum Salicr\'u form. We exhibit that majorization plays a key role
in explaining most of their common features. We give a characterization of the
quantum -entropies under the action of quantum operations, and study
their properties for composite systems. We apply these generalized entropies to
the problem of detection of quantum entanglement, and introduce a discussion on
possible generalized conditional entropies as well.Comment: 26 pages, 1 figure. Close to published versio
High intrinsic energy resolution photon number resolving detectors
Transition Edge Sensors (TESs) are characterized by the intrinsic figure of
merit to resolve both the energy and the statistical distribution of the
incident photons. These properties lead TES devices to become the best single
photon detector for quantum technology experiments. For a TES based on titanium
and gold has been reached, at telecommunication wavelength, an unprecedented
intrinsic energy resolution (0.113 eV). The uncertainties analysis of both
energy resolution and photon state assignment has been discussed. The thermal
properties of the superconductive device have been studied by fitting the bias
curve to evaluate theoretical limit of the energy resolution
Collision entropy and optimal uncertainty
We propose an alternative measure of quantum uncertainty for pairs of
arbitrary observables in the 2-dimensional case, in terms of collision
entropies. We derive the optimal lower bound for this entropic uncertainty
relation, which results in an analytic function of the overlap of the
corresponding eigenbases. Besides, we obtain the minimum uncertainty states. We
compare our relation with other formulations of the uncertainty principle.Comment: The manuscript has been accepted for publication as a Regular Article
in Physical Review
General entropy-like uncertainty relations in finite dimensions
We revisit entropic formulations of the uncertainty principle for an
arbitrary pair of positive operator-valued measures (POVM) and , acting
on finite dimensional Hilbert space. Salicr\'u generalized
-entropies, including R\'enyi and Tsallis ones among others, are used
as uncertainty measures associated with the distribution probabilities
corresponding to the outcomes of the observables. We obtain a nontrivial lower
bound for the sum of generalized entropies for any pair of entropic
functionals, which is valid for both pure and mixed states. The bound depends
on the overlap triplet with (resp. ) being the
overlap between the elements of the POVM (resp. ) and the
overlap between the pair of POVM. Our approach is inspired by that of de
Vicente and S\'anchez-Ruiz [Phys.\ Rev.\ A \textbf{77}, 042110 (2008)] and
consists in a minimization of the entropy sum subject to the Landau-Pollak
inequality that links the maximum probabilities of both observables. We solve
the constrained optimization problem in a geometrical way and furthermore, when
dealing with R\'enyi or Tsallis entropic formulations of the uncertainty
principle, we overcome the H\"older conjugacy constraint imposed on the
entropic indices by the Riesz-Thorin theorem. In the case of nondegenerate
observables, we show that for given , the bound
obtained is optimal; and that, for R\'enyi entropies, our bound improves
Deutsch one, but Maassen-Uffink bound prevails when .
Finally, we illustrate by comparing our bound with known previous results in
particular cases of R\'enyi and Tsallis entropies
Generalized Entropic Uncertainty Relations with Tsallis' Entropy
A generalization of the entropic formulation of the Uncertainty Principle of Quantum Mechanics is considered with the introduction of the q-entropies recently proposed by Tsallis. The concomitant generalized measure is illustrated for the case of phase and number operators in quantum optics. Interesting results are obtained when making use of q-entropies as the basis for constructing generalized entropic uncertainty measures
Natural Metric for Quantum Information Theory
We study in detail a very natural metric for quantum states. This new
proposal has two basic ingredients: entropy and purification. The metric for
two mixed states is defined as the square root of the entropy of the average of
representative purifications of those states. Some basic properties are
analyzed and its relation with other distances is investigated. As an
illustrative application, the proposed metric is evaluated for 1-qubit mixed
states.Comment: v2: enlarged; presented at ISIT 2008 (Toronto
Graphene edge method for three-dimensional probing of Raman microscopes focal volumes
In this work, a layer of graphene was used as a standard material for the measurement of the dimensions of Raman microscopes focal volumes of different confocal Raman spectrometers equipped with different objectives and excitation laser wavelengths. This method consists in probing the volume near the focal point of the system by using a flat graphene monolayer sheet with a straight edge. Graphene was selected because of its high Raman cross section and mechanically and chemically stability, allowing fast measurements and easy manipulation. In this paper, a method to employ graphene to accurately and precisely measure the three dimensions of the focal volume of a Raman microscope is presented; scanning along the axial and lateral directions, it is possible to reconstruct the three dimensions of the focal volume. Furthermore, these operations can be combined in a single procedure which allows the measurement of projections of the volume on planes parallel to the optical axis. Knowledge of these parameters enable absolute quantification of Raman-active molecules and support high-resolution Raman imaging
Single-photon light detection with transition-edge sensors
Transition-Edge Sensors (TESs) are microcalorimeters that measure the energy of incident single photons by the resistance increase of a superconducting film biased within the superconducting-to-normal transition. TES are able to detect single photons from IR to X-ray with an intrinsic energy resolution and photon-number discrimination capability. Metrology, astronomy and quantum
communication are the fields where these properties can be particularly useful. In this work, we report about characterization of different TESs based on Ti films. Single photons have been detected from 200nm to 800 nm working at transition temperature Tc ∼ 100 mK. Using a pulsed laser at 690nm we have demonstrated the capability to resolve up to five photons
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