Solid-State Quantum Communication With Josephson Arrays

Josephson junction arrays can be used as quantum channels to transfer quantum information between distant sites. In this work we discuss simple protocols to realize state transfer with high fidelity. The channels do not require complicate gating but use the natural dynamics of a properly designed array. We investigate the influence of static disorder both in the Josephson energies and in the coupling to the background gate charges, as well as the effect of dynamical noise. We also analyze the readout process, and its backaction on the state transfer

Steady-state entanglement activation in optomechanical cavities

Quantum discord, and a number of related indicators, are currently raising a relentless interest as a novel paradigm of non-classical correlations beyond entanglement. Beside merely fundamental aspects, various works have shown that discord is a valuable -- so far largely unexplored -- resource in quantum information processing. Along this line, quite a striking scheme is {entanglement activation}. An initial amount of discord between two disentangled parties of a multipartite system affects the dynamics so as to establish entanglement across a bipartition, which would not arise otherwise. To date, such a process was proven to be achievable only dynamically, i.e., with no guarantee of a stationary entanglement throughput in the presence of noise. Here, we discover a {\it discord-activated mechanism yielding steady-state entanglement} production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.Comment: 5+4 pages, 5+1 figures (main text + supplementary materials

Full Counting Statistics in Strongly Interacting Systems: Non-Markovian Effects

We present a theory of full counting statistics for electron transport through interacting electron systems with non-Markovian dynamics. We illustrate our approach for transport through a single-level quantum dot and a metallic single-electron transistor to second order in the tunnel-coupling strength, and discuss under which circumstances non-Markovian effects appear in the transport properties.Comment: 4 pages, 2 figures, LaTeX; typos added, references adde

Adiabatic dynamics of a quantum critical system coupled to an environment: Scaling and kinetic equation approaches

We study the dynamics of open quantum many-body systems driven across a critical point by quenching an Hamiltonian parameter at a certain velocity. General scaling laws are derived for the density of excitations and energy produced during the quench as a function of quench velocity and bath temperature. The scaling laws and their regimes of validity are verified for the XY spin chain locally coupled to bosonic baths. A detailed derivation and analysis of the kinetic equation of the problem is presented.Comment: 15 pages, 13 figure

Adiabatic dynamics in open quantum critical many-body systems

The purpose of this work is to understand the effect of an external environment on the adiabatic dynamics of a quantum critical system. By means of scaling arguments we derive a general expression for the density of excitations produced in the quench as a function of its velocity and of the temperature of the bath. We corroborate the scaling analysis by explicitly solving the case of a one-dimensional quantum Ising model coupled to an Ohmic bath.Comment: 4 pages, 4 figures; revised version to be published in Phys. Rev. Let

NNLO Logarithmic Expansions and High Precision Determinations of the QCD background at the LHC: The case of the Z resonance

New methods of solutions of the DGLAP equation and their implementation through NNLO in QCD are briefly reviewed. We organize the perturbative expansion that describes in $x$-space the evolved parton distributions in terms of scale invariant functions, which are determined recursively, and logarithms of the ratio of the running couplings at the initial and final evolution scales. Resummed solutions are constructed within the same approach and involve logarithms of more complex functions, which are given in the non-singlet case. Differences in the evolution schemes are shown to be numerically sizeable and intrinsic to perturbation theory. We illustrate these points in the case of Drell-Yan lepton pair production near the Z resonance, analysis that can be extended to searches of extra $Z^{\prime}$. We show that the reduction of the NNLO cross section compared to the NLO prediction may be attributed to the NNLO evolution.Comment: 5 pages, 2 figures. Talk given at QCD@work 2007, Martina Franca, Italy, 16-20 June 2007. To be published in the American Institute of Physics (AIP) conference proceeding

A new light boson from MAGIC observations?

Recent detection of blazar 3C279 by MAGIC has confirmed previous indications by H.E.S.S. that the Universe is more transparent to very-high-energy gamma rays than currently thought. This circumstance can be reconciled with observations of nearby blazars provided that photon oscillations into a very light Axion-Like Particle occur in extragalactic magnetic fields. The emerging "DARMA scenario" can be tested in the near future by the satellite-borne Fermi LAT detector as well as by the ground-based Imaging Atmospheric Cherenkov Telescopes H.E.S.S., MAGIC, CANGAROO III, VERITAS and by the Extensive Air Shower arrays ARGO-YBJ and MILAGRO.Comment: 4 pages, 1 figure, Proceeding of the "Neutrino Oscillation Workshop", Conca Specchiulla, Otranto, Italy, 6-12 September 200

Modeling of river floods in semiarid basins

LAUREA MAGISTRALELo scopo principale di questo studio è testare la risposta di un modello a parametri distribuiti ovvero il FEST (creato al Politecnico di Milano), nel prevedere gli eventi di piena in bacini semi-aridi come nel nostro caso di studio ovvero la Catalogna. Infatti tale modello fu creato pensando alla previsione di piene per bacini montani, alpini, o comunque con caratteristiche climatiche e morfologiche diverse da quelli in esame. I bacini esaminati hanno appunto caratteristiche particolari essendo prevalentemente caratterizzati da terreni carsici e soggetti a lunghi periodi estivi di siccità, a cui seguono piogge di intensità molto alta che in poche ore possono riversare una quantità di pioggia maggiore alle piogge medie di altri periodi dell’anno, e in lasso di tempo minore, causando eventi chiamati Flash-flood . Questi eventi sono fondamentali da studiare in quanto inducono spesso danni ingenti a cose e persone vista la loro difficile prevedibilità dovuta principalmente al tempo di risposta (lag time) della creazione del deflusso superficiale molto basso, con portate di picco molto alte. Prima si è studiata la risposta iniziale del modello ( calibrandolo e validandolo ) senza apportare modifiche al codice, e si è cercato di individuare quali siano i fattori su cui intervenire per ‘’adattarlo’’ a questo tipo di bacini. Successivamente dopo le opportune modifiche al codice come spiegato più avanti , è stato ripetuto lo stesso procedimento (calibrazione e validazione) ma in una maniera particolare e si è arrivati a un buon risultato di adattabilità.The principal aim of this study is to taste the answer of one distributed physically-based rainfall/runoff hydrological model like FEST-WB (created in Politecnico of Milan), for forecast of flash-flood events in semi-arid basins, like our area of study or rather Catalonia region . Infact originally the FEST model was created to forecast flood events for mountain’s basins of the alpes, so with different climatics and morphologicals features from those examinated in this work. The examinated basins have particular characteristics, being mainly compounds by karst terrains, and subject to long summer droughts followed by very high intensity rains that in a few hours can pour a quantity of rainfalls that can account for a very large fraction of the annual amounts, causing events called Flash-flood. These type of events are importants to understand and to study, because often cause extensive damages to property and people given their difficult predictability, due principally to the short lag-time answer of basins to the intense rainfalls in the creation of runoffs, also characterized by very high peak discharges that are very dangerous for the population. First we studied the model’s answer calibrating and validating it in the originally way, using the originally code or settings of FEST-WB and we try to understand on which parameter we had to intervene to adapt the model at these type of basins. We identified it in the Strickler coefficient. Afterwards we modified the code , calibrating the Strickler coefficient how explained in our work, and we calibrated and validated the model in a different way from the standard method, following Borga et al 2007

Superconducting proximity effect in interacting quantum dots revealed by shot noise

We study the full counting statistics of charge transport through a quantum dot tunnel-coupled to one normal and one superconducting lead with a large superconducting gap. As function of the level detuning, there is a crossover from a regime with strong superconducting correlations in the quantum dot to a regime in which the proximity effect on the quantum dot is suppressed. We analyze the current fluctuations of this crossover in the shot-noise regime. In particular, we predict that the full counting statistics changes from Poissonian with charge 2e, typical for Cooper pairs, to Poissonian with charge e, when the superconducting proximity effect is present. Thus, the onset of the superconducting proximity effect is revealed by the reduction of the Fano factor from 2 to 1.Comment: 5 pages, 3 figure