Experimental observation of the X-shaped near field spatio-temporal correlation of ultra-broadband twin beams

In this work we present the experimental observation of the non factorable near field spatio-temporal correlation of ultra-broadband twin beams generated by parametric down conversion (PDC), in an interferometric-type experiment using sum frequency generation, where both the temporal and spatial degrees of freedom of PDC light are controlled with very high resolution. The revealed X-structure of the correlation is in accordance with the predictions of the theory.Comment: 5 pages, 3 figure

Detection of the ultranarrow temporal correlation of twin beams via sum-frequency generation

We demonstrate the ultranarrow temporal correlation (6 fs full width half maximum) of twin beams generated by parametric down-conversion, by using the inverse process of sum-frequency generation. The result relies on an achromatic imaging of a huge bandwith of twin beams and on a careful control of their spatial degrees of freedom. The detrimental effects of spatial filtering and of imperfect imaging are shown toghether with the theoretical model used to describe the results

Quantum spatial correlations in high-gain parametric down-conversion measured by means of a CCD camera

We consider travelling-wave parametric down-conversion in the high-gain regime and present the experimental demonstration of the quantum character of the spatial fluctuations in the system. In addition to showing the presence of sub-shot noise fluctuations in the intensity difference, we demonstrate that the peak value of the normalized spatial correlations between signal and idler lies well above the line marking the boundary between the classical and the quantum domain. This effect is equivalent to the apparent violation of the Cauchy-Schwartz inequality, predicted by some of us years ago, which represents a spatial analogue of photon antibunching in time. Finally, we analyse numerically the transition from the quantum to the classical regime when the gain is increased and we emphasize the role of the inaccuracy in the determination of the symmetry center of the signal/idler pattern in the far-field plane.Comment: 21 pages, 11 figures, submitted to J. Mod. Opt. special issue on Quantum Imagin

Entropy for Monge-Ampère measures in the prescribed singularities setting

In this note, we generalize the notion of entropy for potentials in a relative full Monge–Amp`ere mass E(X,θ,φ), for a model potential φ. We then investigate stability properties of this condition with respect to blow-ups and perturbation of the cohomology class. We also prove a Moser–Trudinger type inequality with general weight and we show n that functions with finite entropy lie in a relative energy class E n−1 (X, θ, φ) (provided n > 1), while they have the same singularities of φ when n = 1

Per una ricapitalizzazione efficacenete co-creativa dei sistemi territoriali italiani

La trasformazione creativa (innovazione) non dovrebbe essere immaginata se non come emergente dall’interazione interna (immanente) ai soggetti individuali o inter-individuali, piuttosto che da istanze separate e superiori (trascendenti). Il compito del planning dovrebbe quindi essere quello di rendere percepibili le potenzialità di cambiamento emergenti dall’interazione della molteplicità di detentori di quote di capitale urbano (stakeholder), che includono in pratica la totalità dei soggetti, e di fornire loro validi framework di orientamento e di scambio tra differenti, e spesso inconciliabili, sistemi di ‘valori’. Sono insomma richiesti approcci innovativi all’‘urbano’, per lo più contrastanti con le tradizionali prassi di investimento infrastrutturale, realizzate a scapito dell’investimento in ‘capitale umano’. Per superare la vieta dicotomia tra approcci top-down e bottom-up appare inoltro opportuno far riferimento a un nuovo modello di governance caratterizzato da reti auto-organizzate assimilabili a un fenomeno spontaneo guidato da processi sociali più che da obiettivi politici. A questo modello social di governance fanno riferimento i cosiddetti Living Lab urbani e territoriali, da considerare come veri e propri ecosistemi di agenzie che, interagendo co-creativamente, sembrano poter costituire un utile riferimento per l’integrazione multi scalare dei livelli di governo e che, attraverso la condivisione di un’idea di impresa e/o di una problematica, sembrano anche in grado di produrre concreti effetti di rigenerazione urbano-territoriale

Disclosing the spatio-temporal structure of PDC entanglement through frequency up-conversion

In this work we propose and analyse a scheme where the full spatio-temporal correlation of twin photons/beams generated by parametric down-conversion is detected by using its inverse process, i.e. sum frequency generation. Our main result is that, by imposing independently a temporal delay \Delta t and a transverse spatial shift \Delta x between two twin components of PDC light, the up-converted light intensity provides information on the correlation of the PDC light in the full spatio-temporal domain, and should enable the reconstruction of the peculiar X-shaped structure of the correlation predicted in [gatti2009,caspani2010,brambilla2010]. Through both a semi-analytical and a numerical modeling of the proposed optical system, we analyse the feasibility of the experiment and identify the best conditions to implement it. In particular, the tolerance of the phase-sensitive measurement against the presence of dispersive elements, imperfect imaging conditions and possible misalignments of the two crystals is evaluated.Comment: 20 pages, 19 figure

Space-Time Recovery of Arbitrarily Shaped Wave-Packets by Means of Three Dimensional Imaging Technique

We study numerically and experimentally self-focusing dynamics of femtosecond light pulses. By demonstrating the potential of three dimensional imaging technique for quantitative recovery of complex (arbitrarily shaped) wave packets, we monitor space-time transformation dynamics of 150-fs light pulse, which undergoes self-focusing and filamentation in water. Peculiar spatiotemporal and spectral features reveal conical nature of resulting wave-packet

Conical emission, pulse splitting and X-wave parametric amplification in nonlinear dynamics of ultrashort light pulses

The precise observation of the angle-frequency spectrum of light filaments in water reveals a scenario incompatible with current models of conical emission (CE). Its description in terms of linear X-wave modes leads us to understand filamentation dynamics requiring a phase- and group-matched, Kerr-driven four-wave-mixing process that involves two highly localized pumps and two X-waves. CE and temporal splitting arise naturally as two manifestations of this process