93 research outputs found
Identification of Nonlinear Systems Structured by Wiener-Hammerstein Model
Wiener-Hammerstein systems consist of a series connection including a nonlinear static element sandwiched with two linear subsystems. The problem of identifying Wiener-Hammerstein models is addressed in the presence of hard nonlinearity and two linear subsystems of structure entirely unknown (asymptotically stable). Furthermore, the static nonlinearity is not required to be invertible. Given the system nonparametric nature, the identification problem is presently dealt with by developing a two-stage frequency identification method, involving simple inputs
Single photon quantum cryptography
We report the full implementation of a quantum cryptography protocol using a
stream of single photon pulses generated by a stable and efficient source
operating at room temperature. The single photon pulses are emitted on demand
by a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. The
quantum bit error rate is less that 4.6% and the secure bit rate is 9500
bits/s. The overall performances of our system reaches a domain where single
photons have a measurable advantage over an equivalent system based on
attenuated light pulses.Comment: 4 pages, 3 figure
Room temperature stable single-photon source
We report on the realization of a stable solid state room temperature source
for single photons. It is based on the fluorescence of a single
nitrogen-vacancy (NV) color center in a diamond nanocrystal. Antibunching has
been observed in the fluorescence light under both continuous and pulsed
excitation. Our source delivers 2*10^4 single-photon pulses per second at an
excitation repetition rate of 10 MHz. The number of two-photon pulses is
reduced by a factor of five compared to strongly attenuated coherent sources.Comment: 7 pages, 10 figures, accepted to the special issue of the European
Physical Journal D on "Quantum interference and cryptographic keys: novel
physics and advancing technologies", proceedings of the conference QUICK 200
Homodyne estimation of Gaussian quantum discord
We address the experimental estimation of Gaussian quantum discord for
two-mode squeezed thermal state, and demonstrate a measurement scheme based on
a pair of homodyne detectors assisted by Bayesian analysis which provides
nearly optimal estimation for small value of discord. Besides, though homodyne
detection is not optimal for Gaussian discord, the noise ratio to the ultimate
quantum limit, as dictacted by the quantum Cramer-Rao bound, is limited to
about 10 dB.Comment: 5+3 pages, 3 figures, published versio
Frequency identification of Wiener systems with Backlash operators using separable least squares estimators
This paper deals with the identification of Wiener models that involve backlash operators
bordered by possibly noninvertible parametric lines. The latter are also allowed to cross each other making possible to account for general-shape static nonlinearities. The linear dynamic subsystem is not-necessarily parametric but is BIBO stable. A frequency identification method is developed that provides estimates of the nonlinear operator parameters as well as estimates of the linear subsystem frequency gain. The method involves standard and separable least squares estimators that all are shown to be consistent. Backlash
operators and memoryless nonlinearities are handled within a unified framework.Preprin
Experimental open air quantum key distribution with a single photon source
We present a full implementation of a quantum key distribution (QKD) system
with a single photon source, operating at night in open air. The single photon
source at the heart of the functional and reliable setup relies on the pulsed
excitation of a single nitrogen-vacancy color center in diamond nanocrystal. We
tested the effect of attenuation on the polarized encoded photons for inferring
longer distance performance of our system. For strong attenuation, the use of
pure single photon states gives measurable advantage over systems relying on
weak attenuated laser pulses. The results are in good agreement with
theoretical models developed to assess QKD security
Non-Gaussianity of quantum states: an experimental test on single-photon added coherent states
Non Gaussian states and processes are useful resources in quantum information
with continuous variables. An experimentally accessible criterion has been
proposed to measure the degree of non Gaussianity of quantum states, based on
the conditional entropy of the state with a Gaussian reference. Here we adopt
such criterion to characterise an important class of non classical states,
single-photon added coherent states. Our studies demonstrate the reliability
and sensitivity of this measure, and use it to quantify how detrimental is the
role of experimental imperfections in our realisation
On the distillation and purification of phase-diffused squeezed states
Recently it was discovered that non-Gaussian decoherence processes, such as
phase-diffusion, can be counteracted by purification and distillation protocols
that are solely built on Gaussian operations. Here, we make use of this
experimentally highly accessible regime, and provide a detailed experimental
and theoretical analysis of several strategies for purification/distillation
protocols on phase-diffused squeezed states. Our results provide valuable
information for the optimization of such protocols with respect to the choice
of the trigger quadrature, the trigger threshold value and the probability of
generating a distilled state
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