High-sensitivity imaging with multi-mode twin beams

Twin entangled beams produced by single-pass parametric down-conversion (PDC) offer the opportunity to detect weak amount of absorption with an improved sensitivity with respect to standard techniques which make use of classical light sources. We propose a differential measurement scheme which exploits the spatial quantum correlation of type II PDC to image a weak amplitude object with a sensitivity beyond the standard quantum limit imposed by shot-noise.Comment: 13 pages, 8 figure

Triggering Active Galactic Nuclei in Hierarchical Galaxy Formation: Disk instability vs. Interactions

Using a semi analytic model for galaxy formation we investigate the effects of Black Hole accretion triggered by disk instabilities (DI) in isolated galaxies on the evolution of AGN. Specifically, we took on, developed and expanded the Hopkins & Quataert (2011) model for the mass inflow following disk perturbations, and compare the corresponding evolution of the AGN population with that arising in a scenario where galaxy interactions trigger AGN (IT mode). We extended and developed the DI model by including different disk surface density profiles, to study the maximal contribution of DI to the evolution of the AGN population. We obtained the following results: i) for luminosities corresponding to $M_{1450}\gtrsim -26$ the DI mode can provide the BH accretion needed to match the observed AGN luminosity functions up to $z \approx 4.5$; in such a luminosity range and redshift, it can compete with the IT scenario as the main driver of cosmological evolution of AGN; ii) The DI scenario cannot provide the observed abundance of high-luminosity QSO with $M_{1450}\lesssim -26$ AGN, as well as the abundance of high-redhshift $z \approx 4.5$ QSOs with $M_{1450}\lesssim -24$, while the IT scenario provides an acceptable match up to $z \approx 6$, as found in our earliest works; iii) The dispersion of the distributions of Eddington ratio for low- and intermediate-luminosity AGN (bolometric $L_{AGN}$ = $10^{43}$ - $10^{45}$ erg/s) is predicted to be much smaller in the DI scenario compared to the IT mode; iv) The above conclusions are robust with respect to the explored variants of the Hopkins & Quataert (2011) model. We discuss the physical origin of our findings, and how it is possible to pin down the dominant fueling mechanism in the low-intermediate luminosity range $M_{1450}\gtrsim -26$ where both the DI and the IT modes are viable candidates as drivers for the AGN evolution.Comment: Accepted for publication in Astronomy & Astrophysics, 24 pages, 8 figures; updated reference

Dimensionality of the spatio-temporal entanglement of PDC photon pairs

In this work the Schmidt number of the two-photon state generated by parametric-down conversion (PDC) is evaluated in the framework of a fully spatio-temporal model for PDC. A comparison with the results obtained in either purely spatial or purely temporal models shows that the degree of entanglement of the PDC state cannot be trivially reduced to the product of the Schmidt numbers obtained in models with lower dimensionality, unless the detected bandwidth is very narrow. This result is a consequence of the non-factorability of the state in the spatial and temporal degrees of freedoms of twin photons. In the limit of a broad pump beam, we provide a geometrical interpretation of the Schmidt number, as the ratio between the volume of the phase matching region and of a correlation volume.Comment: 17 pages, 10 figures. Submitted to Phys. Rev.

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

RF performance measurement of the DSS-14 70-meter antenna at C-band/L-band

The calibration of the 70-meter antenna at C-band (5.01 GHz) and L-band (1.668 GHz) is described. This calibration comes after a modification to an existing L-band feed to include the C-band frequencies. The test technique employs noise-adding radiometers and associated equipment running simultaneously at both frequencies. The test procedure is described including block diagrams, and results are presented for efficiency, system temperature, and pointing

Sintered silicon nitrode recuperator fabrication

The preliminary design and a demonstration of the feasibility of fabricating submodules of an automotive Stirling engine recuperator for waste heat recovery at 370 C are described. Sinterable silicon nitride (Sialon) tubing and plates were fabricated by extrusion and hydrostatic pressing, respectively, suitable for demonstrating a potential method of constructing ceramic recuperator-type heat exchangers. These components were fired in nitrogen atmosphere to 1800 C without significant scale formation so that they can be used in the as-fired condition. A refractory glass composition (Al2O3 x 4.5 CaO.MgO x 11SiO2) was used to join and seal component parts by a brazing technique which formed strong recuperator submodules capable of withstanding repeated thermal cycling to 1370 C. The corrosion resistance of these materials to Na2SO4 + NaCl carbon mixtures was also assessed in atmospheres of air, hydrogen and CO2-N2-H2O mixtures at both 870 C and 1370 C for times to 1000 hours. No significant reaction was observed under any of these test conditions