269 research outputs found
Quantum Correlation Bounds for Quantum Information Experiments Optimization: the Wigner Inequality Case
Violation of modified Wigner inequality by means binary bipartite quantum
system allows the discrimination between the quantum world and the classical
local-realistic one, and also ensures the security of Ekert-like quantum key
distribution protocol. In this paper we study both theoretically and
experimentally the bounds of quantum correlation associated to the modified
Wigner's inequality finding the optimal experimental configuration for its
maximal violation. We also extend this analysis to the implementation of
Ekert's protocol
Dephasing by a nonstationary classical intermittent noise
We consider a new phenomenological model for a classical
intermittent noise and study its effects on the dephasing of a two-level
system. Within this model, the evolution of the relative phase between the
states is described as a continuous time random walk (CTRW). Using
renewal theory, we find exact expressions for the dephasing factor and identify
the physically relevant various regimes in terms of the coupling to the noise.
In particular, we point out the consequences of the non-stationarity and
pronounced non-Gaussian features of this noise, including some new anomalous
and aging dephasing scenarii.Comment: Submitted to Phys. Rev.
Experiment Investigating the Connection between Weak Values and Contextuality
Weak value measurements have recently given rise to a large interest for both
the possibility of measurement amplification and the chance of further quantum
mechanics foundations investigation. In particular, a question emerged about
weak values being proof of the incompatibility between Quantum Mechanics and
Non-Contextual Hidden Variables Theories (NCHVT). A test to provide a
conclusive answer to this question was given in [M. Pusey, Phys. Rev. Lett.
113, 200401 (2014)], where a theorem was derived showing the NCHVT
incompatibility with the observation of anomalous weak values under specific
conditions. In this paper we realize this proposal, clearly pointing out the
strict connection between weak values and the contextual nature of Quantum
Mechanics.Comment: 5 pages, 4 figure
Reply to Comment on "Quantum dense key distribution"
In this Reply we propose a modified security proof of the Quantum Dense Key
Distribution protocol detecting also the eavesdropping attack proposed by
Wojcik in his Comment.Comment: To appear on PRA with minor change
Direct experimental observation of nonclassicality in ensembles of single photon emitters
In this work we experimentally demonstrate for the first time a recently
proposed criterion adressed to detect nonclassical behavior in the fluorescence
emission of ensembles of single-photon emitters. In particular, we apply the
method to study clusters of NV centres in diamond observed via
single-photon-sensitive confocal microscopy. Theoretical considerations on the
behavior of the parameter at any arbitrary order in presence of poissonian
noise are presented and, finally, the opportunity of detecting manifold
coincidences is discussed
Towards joint reconstruction of noise and losses in quantum channels
The calibration of a quantum channel, i.e. the determination of the
transmission losses affecting it, is definitely one of the principal objectives
in both the quantum communication and quantum metrology frameworks. Another
task of the utmost relevance is the identification, e.g. by extracting its
photon number distribution, of the noise potentially present in the channel.
Here we present a protocol, based on the response of a photon-number-resolving
detector at different quantum efficiencies, able to accomplish both of these
tasks at once, providing with a single measurement an estimate of the
transmission losses as well as the photon statistics of the noise present in
the exploited quantum channel. We show and discuss the experimental results
obtained in the practical implementation of such protocol, with different kinds
and levels of noise.Comment: 6 pages, 4 figure
Positive Operator-Valued Measure reconstruction of a beam-splitter tree based photon-number-resolving detector
Here we present a reconstruction of the Positive Operator-Value Measurement
of a photon-number-resolving detector comprised of three 50:50 beamsplitters in
a tree configuration, terminated with four single-photon avalanche detectors.
The four detectors' outputs are processed by an electronic board that
discriminates detected photon number states from 0 to 4 and implements a "smart
counting" routine to compensate for dead time issues at high count rates
Experimental evidence for bounds on quantum correlations
We implemented the experiment proposed by Cabello [arXiv:quant-ph/0309172] to
test the bounds of quantum correlation. As expected from the theory we found
that, for certain choices of local observables, Cirel'son's bound of the
Clauser-Horne-Shimony-Holt inequality () is not reached by any
quantum states.Comment: RevTex style, 4 pages, 4 figures, to appear on PRL with minor
revisio
Electron quantum optics : partitioning electrons one by one
We have realized a quantum optics like Hanbury Brown and Twiss (HBT)
experiment by partitioning, on an electronic beam-splitter, single elementary
electronic excitations produced one by one by an on-demand emitter. We show
that the measurement of the output currents correlations in the HBT geometry
provides a direct counting, at the single charge level, of the elementary
excitations (electron/hole pairs) generated by the emitter at each cycle. We
observe the antibunching of low energy excitations emitted by the source with
thermal excitations of the Fermi sea already present in the input leads of the
splitter, which suppresses their contribution to the partition noise. This
effect is used to probe the energy distribution of the emitted wave-packets.Comment: 5 pages, 4 figure
Action minimizing orbits in the n-body problem with simple choreography constraint
In 1999 Chenciner and Montgomery found a remarkably simple choreographic
motion for the planar 3-body problem (see \cite{CM}). In this solution 3 equal
masses travel on a eight shaped planar curve; this orbit is obtained minimizing
the action integral on the set of simple planar choreographies with some
special symmetry constraints. In this work our aim is to study the problem of
masses moving in \RR^d under an attractive force generated by a potential
of the kind , , with the only constraint to be a simple
choreography: if are the orbits then we impose the
existence of x \in H^1_{2 \pi}(\RR,\RR^d) such that q_i(t)=x(t+(i-1) \tau),
i=1,...,n, t \in \RR, where . In this setting, we first
prove that for every d,n \in \NN and , the lagrangian action
attains its absolute minimum on the planar circle. Next we deal with the
problem in a rotating frame and we show a reacher phenomenology: indeed while
for some values of the angular velocity minimizers are still circles, for
others the minima of the action are not anymore rigid motions.Comment: 24 pages; 4 figures; submitted to Nonlinearit
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