A complete characterisation of the heralded noiseless amplification of photons

Heralded noiseless amplifcation of photons has recently been shown to provide a means to overcome losses in complex quantum communication tasks. In particular, to overcome transmission losses that could allow for the violation of a Bell inequality free from the detection loophole, for Device Independent Quantum Key Distribution (DI-QKD). Several implementations of a heralded photon amplifier have been proposed and the first proof of principle experiments realised. Here we present the first full characterisation of such a device to test its functional limits and potential for DI-QKD. This device is tested at telecom wavelengths and is shown to be capable of overcoming losses corresponding to a transmission through $20\, \rm km$ of single mode telecom fibre. We demonstrate heralded photon amplifier with a gain $>100$ and a heralding probability $>83$, required by DI-QKD protocols that use the Clauser-Horne-Shimony-Holt (CHSH) inequality. The heralded photon amplifier clearly represents a key technology for the realisation of DI-QKD in the real world and over typical network distances.Comment: 9 pages, 4 figure

Local search for stable marriage problems

The stable marriage (SM) problem has a wide variety of practical applications, ranging from matching resident doctors to hospitals, to matching students to schools, or more generally to any two-sided market. In the classical formulation, n men and n women express their preferences (via a strict total order) over the members of the other sex. Solving a SM problem means finding a stable marriage where stability is an envy-free notion: no man and woman who are not married to each other would both prefer each other to their partners or to being single. We consider both the classical stable marriage problem and one of its useful variations (denoted SMTI) where the men and women express their preferences in the form of an incomplete preference list with ties over a subset of the members of the other sex. Matchings are permitted only with people who appear in these lists, an we try to find a stable matching that marries as many people as possible. Whilst the SM problem is polynomial to solve, the SMTI problem is NP-hard. We propose to tackle both problems via a local search approach, which exploits properties of the problems to reduce the size of the neighborhood and to make local moves efficiently. We evaluate empirically our algorithm for SM problems by measuring its runtime behaviour and its ability to sample the lattice of all possible stable marriages. We evaluate our algorithm for SMTI problems in terms of both its runtime behaviour and its ability to find a maximum cardinality stable marriage.For SM problems, the number of steps of our algorithm grows only as O(nlog(n)), and that it samples very well the set of all stable marriages. It is thus a fair and efficient approach to generate stable marriages.Furthermore, our approach for SMTI problems is able to solve large problems, quickly returning stable matchings of large and often optimal size despite the NP-hardness of this problem.Comment: 12 pages, Proc. COMSOC 2010 (Third International Workshop on Computational Social Choice

Non-homogeneous hydrogen deflagrations in small scale enclosure. Experimental results

Abstract University of Pisa performed hydrogen releases and deflagrations in a 1.14 m3 test facility, which shape and dimensions resemble a gas cabinet. Tests were performed for the HySEA project, founded by the Fuel Cells and Hydrogen 2 Joint Undertaking with the aim to conduct pre-normative research on vented deflagrations in enclosures and containers used for hydrogen energy applications. The test facility, named Small Scale Enclosure (SSE), has a vent area of 0,42 m2 which can host different types of vent; plastic sheet and commercial vent were tested. Realistic levels of congestion are obtained placing a number of gas bottles inside the enclosure. Releases are performed from a buffer tank of a known volume filled with hydrogen at a pressure ranging between 15 and 60 bar. Two nozzles of different diameter and three different release directions were tested, being the nozzle placed at a height where in a real application a leak has the highest probability to occur. Three different ignition locations were investigated as well. This paper is aimed to summarize the main features of the experimental campaign as well as to present its results

Recent developments of the Hierarchical Reference Theory of Fluids and its relation to the Renormalization Group

The Hierarchical Reference Theory (HRT) of fluids is a general framework for the description of phase transitions in microscopic models of classical and quantum statistical physics. The foundations of HRT are briefly reviewed in a self-consistent formulation which includes both the original sharp cut-off procedure and the smooth cut-off implementation, which has been recently investigated. The critical properties of HRT are summarized, together with the behavior of the theory at first order phase transitions. However, the emphasis of this presentation is on the close relationship between HRT and non perturbative renormalization group methods, as well as on recent generalizations of HRT to microscopic models of interest in soft matter and quantum many body physics.Comment: 17 pages, 5 figures. Review paper to appear in Molecular Physic

Analysis of the influence of geometric and ventilation factors on indoor pollutant dispersion: a numerical study

The aim of this study is to delineate the role played by natural ventilation and room geometry on indoor dispersion. To this end, particle material (PM) concentration fields obtained using Computational Fluid Dynamics (CFD) concerning a series of ideal cases regarding parallelepiped rooms of different sizes and inlet velocities at the openings have been analysed. The numerical results have been compared with the concentrations obtained using a Box Model based on the mass balance. The results show a reasonably good agreement between the emptying times of the rooms calculated by the CFD and the Box Model, particularly when the room is square shaped. It was also found that the emptying time assumes an almost constant value once normalized with the inlet velocity and room diagonal. Since these are known values, it is possible to infer the emptying time avoiding the use of highly time-consuming numerical simulations

Description of chemical transport in laboratory rock cores using the continuous random walk formalism

We investigate chemical transport in laboratory rock cores using unidirectional pulse tracer experiments. Breakthrough curves (BTCs) measured at various flow rates in one sandstone and two carbonate samples are interpreted using the one-dimensional Continuous Time Random Walk (CTRW) formulation with a truncated power law (TPL) model. Within the same framework, we evaluate additional memory functions to consider the Advection-Dispersion Equation (ADE) and its extension to describe mass exchange between mobile and immobile solute phases (Single-Rate Mass Transfer model, SRMT). To provide physical constraints to the models, parameters are identified that do not depend on the flow rate. While the ADE fails systematically at describing the effluent profiles for the carbonates, the SRMT and TPL formulations provide excellent fits to the measurements. They both yield a linear correlation between the dispersion coefficient and the Péclet number (DL Pe for 10 < (Pe) < 100), and the longitudinal dispersivity is found to be significantly larger than the equivalent grain diameter, De. The BTCs of the carbonate rocks show clear signs of nonequilibrium effects. While the SRMT model explicitly accounts for the presence of microporous regions (up to 30% of the total pore space), in the TPL formulation the time scales of both advective and diffusive processes (t1 (Pe) and t2) are associated with two characteristic heterogeneity length scales (d and l, respectively). We observed that l 2.5 × De and that anomalous transport arises when ld (1). In this context, the SRMT and TPL formulations provide consistent, yet complementary, insight into the nature of anomalous transport in laboratory rock cores