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

A bibliometric analysis of the Aga Khan University Research Contribution in Early Child Development

The research contribution of the Aga Khan University to the Sustainable Development Goals (SDGs) has been explored through a bibliometric analysis. The analysis shows exponential growth of research across the SDGs undertaken by AKU-affiliated researchers. The analysis identified areas of interdisciplinary research, with a significant focus on societal development of interest to AKU, as per its mandate, and reflective of the work of the Aga Khan Development Network (AKDN) of which AKU is an integral part. Building on the bibliometric analysis, this paper focuses on early childhood development and early childhood education with reference to the SDGs. A specific query is undertaken on ECD with respect to SDG 4 (Education) with an in-depth review of ECD reflective of AKU’s research output, 2016-2019. The paper presents an analysis of publications by AKU-affiliated authors as indexed in Scopus, a citation database of peer-reviewed literature, which indexes over 15,000 titles. This study presents bibliometric indicators including trends in high-impact publications along with citation analyses of articles, h-index, journal rank, impact factor and societal impact through analysing articles published in open access journals. In undertaking this study and reflecting on the themes of the IHD/CoEWH Conference, the paper makes a scholarly contribution with a specific focus on AKU’s research and scholarship to the areas of ECD and the SDGs. The paper notes areas for further research on ECD and SDGs emanating from this analysis

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

Orbital periods of the binary sdB stars PG0940+068 and PG1247+554

We have used the radial velocity variations of two sdB stars previously reported to be binaries to establish their orbital periods. They are PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are 0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for PG0940+068. The nature of the companions is not constrained further by our data.Comment: 5 pages, 2 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

Plasmon dispersion in layered transition-metal dichalcogenides

Motivated by recent experiments, we perform a microscopic analysis of the dynamical charge response of layered transition-metal dichalcogenides that display a low-temperature charge-density wave (CDW) order. In agreement with measurements, our parameter-free results show a negative in-plane plasmon dispersion that switches to positive slope upon electron (or hole) doping. This finding is explained by the peculiar behavior of the intraband transitions, which are partially suppressed under doping, and it is not linked to the CDW order. Finally, in the direction perpendicular to the layers, we predict the reappearance around the Bragg reflections of the spectra of the first Brillouin zone, a clear effect of the crystal local-field impact. Our results give a general picture of the collective excitations in these materials suggesting a simpler reinterpretation of the experiments

Critical Field of MGB2 : Crossover from Clean to Dirty Regimes

We have studied the upper critical field, Bc2, in poly-crystalline MgB2 samples in which disorder was varied in a controlled way to carry selectively p and s bands from clean to dirty limit. We have found that the clean regime survives when p bands are dirty and s bands are midway between clean and dirty. In this framework we can explain the anomalous behaviour of Al doped samples, in which Bc2 decreases as doping increases.Comment: 11 pages, 2 figure

Spatial entanglement of twin quantum images

We show that the spatial entanglement of two twin images obtained by parametric down conversion is complete, i.e., concerns both amplitude and phase. By considering a homodyne detection scheme, which allows comparison of field quadrature components of the two images pixel by pixel, Einstein-Podolsky Rosen correlations are shown to exist between symmetrical pixels of the two images. The best possible correlation is obtained by adjusting the phase profile of the local oscillator in the amplification area. The results for quadrature components hold even in the absence of any input image, i.e., for pure parametric fluorescence. In this case, they are not related to intensity and phase fluctuations

Detection of sub-shot-noise spatial correlation in high-gain parametric down-conversion

Using a 1GW-1ps pump laser pulse in high gain parametric down-conversion allows us to detect sub-shot-noise spatial quantum correlation with up to one hundred photoelectrons per mode, by means of a high efficiency CCD. The statistics is performed in single-shot over independent spatial replica of the system. The paper highlights the evidence of quantum correlation between symmetrical signal and idler spatial areas in the far field, in the high gain regime. In accordance with the predictions of numerical calculations the observed transition from the quantum to the classical regime is interpreted as a consequence of the narrowing of the down-converted beams in the very high gain regime.Comment: 4,2 pages, 4 figure