Experimental realization of a measurement conditional unitary operation at single photon level and application to detector characterization

Our last experimental results on the realization of a measurement-conditional unitary operation at single photon level are presented. This gate operates by rotating by $90^o$ the polarization of a photon produced by means of Type-II Parametric Down Conversion conditional to a polarization measurement on the correlated photon. We then propose a new scheme for measuring the quantum efficiency of a single photon detection apparatus by using this set-up. We present experimental results obtained with this scheme compared with {\it traditional} biphoton calibration. Our results show the interesting potentiality of the suggested scheme.Comment: to appear in Proc. of SPIE meeting, Denver august 200

Reply to Comment on "Quantum dense key distribution"

In this Reply we propose a modified security proof of the Quantum Dense Key Distribution protocol detecting also the eavesdropping attack proposed by Wojcik in his Comment.Comment: To appear on PRA with minor change

Absolute calibration of Analog Detectors using Stimulated Parametric Down Conversion

Spontaneous parametric down conversion has been largely exploited as a tool for absolute calibration of photon counting detectors, photomultiplier tubes or avalanche photodiodes working in Geiger regime. In this work we investigate the extension of this technique from very low photon flux of photon counting regime to the absolute calibration of analog photodetectors at higher photon flux. Moving toward higher photon rate, i.e. at high gain regime, with the spontaneous parametric down conversion shows intrinsic limitations of the method, while the stimulated parametric down conversion process, where a seed beam properly injected into the crystal in order to increase the photon generation rate in the conjugate arm, allows us to work around this problem. A preliminary uncertainty budget is discussed

Recent experiments performed at "Carlo Novero" lab at INRIM on Quantum Information and Foundations of Quantum Mechanics

In this paper we present some recent work performed at "Carlo Novero" lab on Quantum Information and Foundations of Quantum Mechanics.Comment: Contribution to III international workshop "Recent advances in Foundations of Quantum Mechanics and Quantum Information. In memory of Carlo Novero

Self consistent, absolute calibration technique for photon number resolving detectors

Well characterized photon number resolving detectors are a requirement for many applications ranging from quantum information and quantum metrology to the foundations of quantum mechanics. This prompts the necessity for reliable calibration techniques at the single photon level. In this paper we propose an innovative absolute calibration technique for photon number resolving detectors, using a pulsed heralded photon source based on parametric down conversion. The technique, being absolute, does not require reference standards and is independent upon the performances of the heralding detector. The method provides the results of quantum efficiency for the heralded detector as a function of detected photon numbers. Furthermore, we prove its validity by performing the calibration of a Transition Edge Sensor based detector, a real photon number resolving detector that has recently demonstrated its effectiveness in various quantum information protocols.Comment: 9 pages, 2 figure

Surface oscillations in channeled snow flows

An experimental device has been built to measure velocity profiles and friction laws in channeled snow flows. The measurements show that the velocity depends linearly on the vertical position in the flow and that the friction coefficient is a first-order polynomial in velocity (u) and thickness (h) of the flow. In all flows, oscillations on the surface of the flow were observed throughout the channel and measured at the location of the probes. The experimental results are confronted with a shallow water approach. Using a Saint-Venant modeling, we show that the flow is effectively uniform in the streamwise direction at the measurement location. We show that the surface oscillations produced by the Archimedes's screw at the top of the channel persist throughout the whole length of the channel and are the source of the measured oscillations. This last result provides good validation of the description of such channeled snow flows by a Saint-Venant modeling

Massive stellar systems: observational challenges and perspectives in the E-ELT era

We introduce the empirical framework concerning optical and near-infrared (NIR) photometry of crowded stellar fields. In particular, we address the impact that linear detectors and analytical PSF played in improving the accuracy and the precision of multi-band color-magnitude diagrams (CMDs). We focus our attention on recent findings based on deep NIR images collected with Adaptive Optics (AO) systems at the 8-10m class telescopes and discuss pros and cons of the different approaches. We also discuss the estimate of the absolute age of globular clusters using a well defined knee along the lower main sequence. We mention the role which the current AO-assisted instruments will have in addressing longstanding astrophysical problems of the Galactic center. Finally, we outline the role of first generation of E-ELT instruments upon photometry and spectroscopy of crowded stellar fields