In a very simplistic way, the Command and Control functions can be summarized as the need to provide the decision makers with an exhaustive, real-time, situation picture and the capability to convey their decisions down to the operational forces. This two-ways data and information flow is vital to the execution of current operations and goes far beyond the border of military operations stretching to Police and disaster recovery as well. The availability of off-the shelf technology has enabled hostile elements to endanger the security of the communication networks by violating the traditional security protocols and devices and hacking sensitive databases. In this paper an innovative approach based to implementing Device Independent Quantum Key Distribution system is presented. The use of this technology would prevent security breaches due to a stolen crypto device placed in an end-to-end communication chain. The system, operating with attenuated laser, is practical and provides the increasing of the distance between the legitimate users.
Our main goal is to describe the basic steps for the emission control of the electromagnetic field leaving a tailored slit on a gold film, combined with a plasmonic grating designed on the output face, in order to make the emitted beam acquire the desired irradiation diagram (ID). A suitable numerical tool developed for a fast evaluation of the slit-grating system’s ID allows to spare time in the definition of the selected configurations. The customization of the ID is a primary step for the design of more complex structures with potential useful capabilities for the manipulation of impinging light waves and the consequent rise of interesting electromagnetic patterns.
We present a study on the design, growth and optical characterization of a GaN/AlGaN microcavity for the enhancement
of second order non linear effects. The proposed system exploits the high second order nonlinear optical response of
GaN due to the non centrosymmetric crystalline structure of this material. It consists of a GaN cavity embedded between
two GaN/AlGaN Distributed Bragg Reflectors designed for a reference mode coincident with a second harmonic field
generated in the near UV region (~ 400 nm). Critical issues for this target are the crystalline quality of the material,
together with sharp and abrupt interfaces among the multi-stacked layers. A detailed investigation on the growth
evolution of GaN and AlGaN epilayers in such a configuration is reported, with the aim to obtain high quality factor in
the desiderated spectral range. Non linear second harmonic generation experiments have been performed and the results
were compared with bulk GaN sample, highlighting the effect of the microcavity on the non linear optical response of
this material.
In this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC)
microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two
AlGaN/GaN Distributed Bragg Reflectors on sapphire substrate, designed to generate a λ= 800 nm frequency downconverted
signal (χ(2) effect) from an incident pump signal at λ= 400 nm. The heterostructure was epitaxially grown by
metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which
amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated
1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the
pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based
on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to
achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90°).
Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern
is transferred to the GaN/AlGaN heterostructure.
We present experimental results on noncollinear second harmonic generation from III-V nitrides
structures, discussing the collinear and noncollinear configuration as a function of polarization
state of both fundamental and generated beams .
In this paper we prove both theoretically and experimentally the insecurity of the Ekert’s protocol for quantum-key distribution when based on the Wigner inequality when entangled photon pairs are used as source. The security proof of the Eckert’s protocol based on Wigner’s inequality consists in verifying the violation of W ≥ 0 (which corresponds to local-realistic theories). We highlight that a violation of the Wigner’s inequality occurs when Eve controls the two quantum channels. We give the theoretical motivation for this result and we perform an experiment proving this weakness, by realizing the condition of Eve gaining total control of the source of photon pairs. In addition we calculate the modified version of this inequality which guarantees safe quantum-key distribution, thus proving it experimentally.
We present results of experimental demonstration of secure Quantum Key Distribution (QKD) at Elsag spa based on the implementation of BB84 protocol using polarization entangled states produced in the nonlinear process of type-II spontaneous parametric down conversion (SPDC). This enables us to avoid the use of active polarization modulation components and increases the overall key distribution rate. The high quality of polarization-entangled state generated by parametric down conversion and the high efficiency of coupling entangled-photon pairs into a single-mode optical fiber has enabled us to perform QKD with quantum bit-error rate compatible with acceptable security levels. The complete software system architecture includes a QKD protocol implementing all phases of the key distillation process. The system runs in a server and two users configuration on three different PCs connected over a local area network (LAN). Friendly graphical user interfaces (GUI) are available to start and to monitor the whole key generation and distillation process.
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