Quantum characterization of bipartite Gaussian states

Gaussian bipartite states are basic tools for the realization of quantum information protocols with continuous variables. Their complete characterization is obtained by the reconstruction of the corresponding covariance matrix. Here we describe in details and experimentally demonstrate a robust and reliable method to fully characterize bipartite optical Gaussian states by means of a single homodyne detector. We have successfully applied our method to the bipartite states generated by a sub-threshold type-II optical parametric oscillator which produces a pair of thermal cross-polarized entangled CW frequency degenerate beams. The method provide a reliable reconstruction of the covariance matrix and allows to retrieve all the physical information about the state under investigation. These includes observable quantities, as energy and squeezing, as well as non observable ones as purity, entropy and entanglement. Our procedure also includes advanced tests for Gaussianity of the state and, overall, represents a powerful tool to study bipartite Gaussian state from the generation stage to the detection one

Rigid N=2 superconformal hypermultiplets

We discuss superconformally invariant systems of hypermultiplets coupled to gauge fields associated with target-space isometries.Comment: Invited talk given at the International Seminar "Supersymmetries and Quantum Symmetries", July 1997, Dubna. Latex, 9 p

Couplings of N=1 chiral spinor multiplets

We derive the action for chiral spinor multiplets coupled to vector and scalar multiplets. We give the component form of the action, which contains gauge invariant mass terms for the antisymmetric tensors in the spinor superfield and additional Green-Schwarz couplings to vector fields. We observe that supersymmetry provides mass terms for the scalars in the spinor multiplet which do not arise from eliminating an auxiliary field. We construct the dual action by explicitly performing the duality transformations in superspace and give its component form.Comment: 17 pages, v2 small change

Full characterization of Gaussian bipartite entangled states by a single homodyne detector

We present the full experimental reconstruction of Gaussian entangled states generated by a type--II optical parametric oscillator (OPO) below threshold. Our scheme provides the entire covariance matrix using a single homodyne detector and allows for the complete characterization of bipartite Gaussian states, including the evaluation of purity, entanglement and nonclassical photon correlations, without a priori assumptions on the state under investigation. Our results show that single homodyne schemes are convenient and robust setups for the full characterization of OPO signals and represent a tool for quantum technology based on continuous variable entanglement.Comment: 4 pages, 3 figures, slightly longer version of published PR

Asymptotics of Random Contractions

In this paper we discuss the asymptotic behaviour of random contractions $X=RS$, where $R$, with distribution function $F$, is a positive random variable independent of $S\in (0,1)$. Random contractions appear naturally in insurance and finance. Our principal contribution is the derivation of the tail asymptotics of $X$ assuming that $F$ is in the max-domain of attraction of an extreme value distribution and the distribution function of $S$ satisfies a regular variation property. We apply our result to derive the asymptotics of the probability of ruin for a particular discrete-time risk model. Further we quantify in our asymptotic setting the effect of the random scaling on the Conditional Tail Expectations, risk aggregation, and derive the joint asymptotic distribution of linear combinations of random contractions.Comment: 25 page

An effective method to estimate multidimensional Gaussian states

A simple and efficient method for characterization of multidimensional Gaussian states is suggested and experimentally demonstrated. Our scheme shows analogies with tomography of finite dimensional quantum states, with the covariance matrix playing the role of the density matrix and homodyne detection providing Stern-Gerlach-like projections. The major difference stems from a different character of relevant noises: while the statistics of Stern-Gerlach-like measurements is governed by binomial statistics, the detection of quadrature variances correspond to chi-square statistics. For Gaussian and near Gaussian states the suggested method provides, compared to standard tomography techniques, more stable and reliable reconstructions. In addition, by putting together reconstruction methods for Gaussian and arbitrary states, we obtain a tool to detect the non-Gaussian character of optical signals.Comment: 8 pages, 5 fis, accepted for publication on PR

Application of best estimate plus uncertainty in review of research reactor safety analysis

To construct and operate a nuclear research reactor, the licensee is required to obtain the authorization from the regulatory body. One of the tasks of the regulatory authority is to verify that the safety analysis fulfils safety requirements. Historically, the compliance with safety requirements was assessed using a deterministic approach and conservative assumptions. This provides sufficient safety margins with respect to the licensing limits on boundary and operational conditions. Conservative assumptions were introduced into safety analysis to account for the uncertainty associated with lack of knowledge. With the introduction of best estimate computational tools, safety analyses are usually carried out using the best estimate approach. Results of such analyses can be accepted by the regulatory authority only if appropriate uncertainty evaluation is carried out. Best estimate computer codes are capable of providing more realistic information on the status of the plant, allowing the prediction of real safety margins. The best estimate plus uncertainty approach has proven to be reliable and viable of supplying realistic results if all conditions are carefully followed. This paper, therefore, presents this concept and its possible application to research reactor safety analysis. The aim of the paper is to investigate the unprotected loss-of-flow transients "core blockage" of a miniature neutron source research reactor by applying best estimate plus uncertainty methodology. The results of our calculations show that the temperatures in the core are within the safety limits and do not pose any significant threat to the reactor, as far as the melting of the cladding is concerned. The work also discusses the methodology of the best estimate plus uncertainty approach when applied to the safety analysis of research reactors for licensing purposes

Il Sito Web accessibile dell’Osservatorio Vesuviano

Il sito web dell’Osservatorio Vesuviano (OV) nasce nel 1997. Lo scopo era quello di fornire informazioni sullo stato di attività dei vulcani della Campania, per i quali l’Osservatorio Vesuviano gestisce le reti strumentali di monitoraggio, nonché di far conoscere le attività scientifiche e i dati prodotti dall’ente. Nel 2002 il sito ha subito una sostanziale riorganizzazione, a seguito di una ristrutturazione dell’Osservatorio Vesuviano, che insieme ad altri istituzioni scientifiche affini era confluito, all’inizio del 2001, nell’Istituto Nazionale di Geofisica e Vulcanologia (INGV) diventandone la Sezione di Napoli. La nuova versione ha tenuto conto della più complessa articolazione delle attività dell’Osservatorio Vesuviano, che negli anni aveva visto aumentare il numero dei propri ricercatori e tecnici e aveva ulteriormente differenziato e specializzato le proprie attività. Inoltre la nuova strutturazione come sezione dell’INGV consentiva un’organizzazione in Unità Funzionali e Servizi. In occasione della realizzazione della seconda versione del sito è stata effettuata un’analisi sistematica dell’utenza basata prevalentemente sulla posta elettronica ricevuta all’indirizzo dedicato alle richieste di informazioni da parte del pubblico. Questo ha consentito di individuare diverse tipologie di utenza. In funzione delle crescenti richieste di informazioni è stato inoltre organizzato un gruppo per curare il servizio “info”, basato su richieste di informazione via mail, che ha dato modo di meglio delineare gli argomenti di maggior interesse da parte dei visitatori (Giudicepietro et al., 2006). Questa attività ha fatto nascere anche una sezione dedicata alle domande frequenti che, soprattutto nei periodi di maggior attenzione per le tematiche del rischio vulcanico, è risultata un utile supporto alla richiesta di informazioni da parte del pubblico. Negli ultimi anni in Italia, come in molti altri paesi del mondo, si è sviluppata una normativa in materia di web che ha dettato le linee guida per lo sviluppo dei siti delle Pubbliche Amministrazioni (Circolare Funzione Pubblica 13 marzo 2001, n. 3/2001 “Linee guida per l'organizzazione, l'usabilità e l'accessibilità dei siti web delle pubbliche amministrazioni”) nonché ha richiamato l’attenzione sull’accessibilità. La normativa italiana relativa all’accessibilità ha lo scopo principale di garantire la fruizione delle informazioni diffuse sul web e dei relativi servizi informatici anche alle persone disabili in ottemperanza al principio di uguaglianza ai sensi dell'articolo 3 della Costituzione. In particolare la Legge del 9 gennaio 2004 n. 4 (pubblicata in G.U. 13 del 17.01.2004) definisce l’accessibilità delle fonti di informazione e servizi informatici come “la capacità dei sistemi informatici, nelle forme e nei limiti consentiti dalle conoscenze tecnologiche, di erogare servizi e fornire informazioni fruibili, senza discriminazioni, anche da parte di coloro che a causa di disabilità necessitano di tecnologie assistive o configurazioni particolari”. Le tecnologie assistive sono definite nella stessa legge come “gli strumenti e le soluzioni tecniche, hardware e software, che permettono alla persona disabile, superando o riducendo le condizioni di svantaggio, di accedere alle informazioni e ai servizi erogati dai sistemi informatici”. Un esempio di tecnologia 4 assistiva può essere uno screen reader, ovvero un lettore di schermo, strumento utilizzato dai non vedenti per usare il computer. In attuazione della legge del 9 gennaio 2004 n. 4, il Decreto Ministeriale dell'8 luglio 2005 "Requisiti tecnici e i diversi livelli per l'accessibilità agli strumenti informatici", definisce 22 requisiti per l’accessibilità che i siti delle Pubbliche Amministrazioni devono soddisfare. La seconda versione del sito dell’Osservatorio Vesuviano non era conforme ai requisiti richiesti da questo decreto, pertanto si è resa necessaria una nuova ristrutturazione del sito che consentisse l’adeguamento alla normativa vigente (www.w3.org, www.governo.it, www.pubbliaccesso.it, www.cnipa.gov.it)

More on integrable structures of superstrings in AdS(4) x CP(3) and AdS(2) x S(2) x T(6) superbackgrounds

In this paper we continue the study, initiated in arXiv:1009.3498 and arXiv:1104.1793, of the classical integrability of Green-Schwarz superstrings in AdS(4) x CP(3) and AdS(2) x S(2) x T(6) superbackgrounds whose spectrum contains non-supercoset worldsheet degrees of freedom corresponding to broken supersymmetries in the bulk. We derive an explicit expression, to all orders in the coset fermions and to second order in the non-coset fermions, which extends the supercoset Lax connection in these backgrounds with terms depending on the non-coset fermions. An important property of the obtained form of the Lax connection is that it is invariant under Z_4-transformations of the superisometry generators and the spectral parameter. This demonstrates that the contribution of the non-coset fermions does not spoil the Z_4-symmetry of the super-coset Lax connection which is of crucial importance for the application of Bethe-ansatz techniques. The expressions describing the AdS(4) x CP(3) and AdS(2) x S(2) x T(6) superstring sigma--models and their Lax connections have a very similar form. This is because their amount of target-space supersymmetries complement each other to 32=24+8, the maximal number of 10d type II supersymmetries. As a byproduct, this similarity has allowed us to obtain the form of the geometry of the complete type IIA AdS(2) x S(2) x T(6) superspace to all orders in the coset fermions and to the second order in the non-coset ones.Comment: 28 pages; v2: References adde

Pure Spinor Approach to Type IIA Superstring Sigma Models and Free Differential Algebras

This paper considers the Free Differential Algebra and rheonomic parametrization of type IIA Supergravity, extended to include the BRS differential and the ghosts. We consider not only the ghosts lambda's of supersymmetry but also the ghosts corresponding to gauge and Lorentz transformations. In this way we can derive not only the BRS transformations of fields and ghosts but also the standard pure spinor constraints on lambda's. Moreover the formalism allows to derive the action for the pure spinor formulation of type IIA superstrings in a general background, recovering the action first obtained by Berkovits and Howe.Comment: 1+23 pages, v2: added clarifications and a reference, misprints corrected, v3: presentation improved, results unchange