Dynamics of quantum correlations in colored environments

We address the dynamics of entanglement and quantum discord for two non interacting qubits initially prepared in a maximally entangled state and then subjected to a classical colored noise, i.e. coupled with an external environment characterized by a noise spectrum of the form $1/f^{\alpha}$. More specifically, we address systems where the Gaussian approximation fails, i.e. the sole knowledge of the spectrum is not enough to determine the dynamics of quantum correlations. We thus investigate the dynamics for two different configurations of the environment: in the first case the noise spectrum is due to the interaction of each qubit with a single bistable fluctuator with an undetermined switching rate, whereas in the second case we consider a collection of classical fluctuators with fixed switching rates. In both cases we found analytical expressions for the time dependence of entanglement and quantum discord, which may be also extended to a collection of flcutuators with random switching rates. The environmental noise is introduced by means of stochastic time-dependent terms in the Hamiltonian and this allows us to describe the effects of both separate and common environments. We show that the non-Gaussian character of the noise may lead to significant effects, e.g. environments with the same power spectrum, but different configurations, give raise to opposite behavior for the quantum correlations. In particular, depending on the characteristics of the environmental noise considered, both entanglement and discord display either a monotonic decay or the phenomena of sudden death and revivals. Our results show that the microscopic structure of environment, besides its noise spectrum, is relevant for the dynamics of quantum correlations, and may be a valid starting point for the engineering of non-Gaussian colored environments.Comment: 8 pages, 3 figure

Spatial structures and dynamics of kinetically constrained models for glasses

Kob and Andersen's simple lattice models for the dynamics of structural glasses are analyzed. Although the particles have only hard core interactions, the imposed constraint that they cannot move if surrounded by too many others causes slow dynamics. On Bethe lattices a dynamical transition to a partially frozen phase occurs. In finite dimensions there exist rare mobile elements that destroy the transition. At low vacancy density, $v$, the spacing, $\Xi$, between mobile elements diverges exponentially or faster in $1/v$. Within the mobile elements, the dynamics is intrinsically cooperative and the characteristic time scale diverges faster than any power of $1/v$ (although slower than $\Xi$). The tagged-particle diffusion coefficient vanishes roughly as $\Xi^{-d}$.Comment: 4 pages. Accepted for pub. in Phys. Rev. Let

Experimental estimation of quantum discord for polarization qubit and the use of fidelity to assess quantum correlations

We address the experimental determination of entropic quantum discord for systems made of a pair of polarization qubits. We compare results from full and partial tomography and found that the two determinations are statistically compatible, with partial tomography leading to a smaller value of discord for depolarized states. Despite the fact that our states are well described, in terms of fidelity, by families of depolarized or phase-damped states, their entropic discord may be largely different from that predicted for these classes of states, such that no reliable estimation procedure beyond tomography may be effectively implemented. Our results, together with the lack of an analytic formula for the entropic discord of a generic two-qubit state, demonstrate that the estimation of quantum discord is an intrinsically noisy procedure. Besides, we question the use of fidelity as a figure of merit to assess quantum correlations

Lattice Glass Models

Motivated by the concept of geometrical frustration, we introduce a class of statistical mechanics lattice models for the glass transition. Monte Carlo simulations in three dimensions show that they display a dynamical glass transition which is very similar to that observed in other off-lattice systems and which does not depend on a specific dynamical rule. Whereas their analytic solution within the Bethe approximation shows that they do have a discontinuous glass transition compatible with the numerical observations.Comment: 4 pages, 2 figures; minor change

Lyapunov Pairs in Semilinear Differential Problems with State-Dependent Impulses

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Laser-heater assisted plasma channel formation in capillary discharge waveguides

A method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed. The plasma channel produced by the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis. This interaction creates a deeper plasma channel within the capillary discharge that evolves on a ns-time scale, allowing laser beams with smaller spot sizes than would otherwise be possible in the unmodified capillary discharge.Comment: 5 pages, 3 figure

Un alimentatore solare per stazioni remote

Un alimentatore solare può essere un oggetto sofisticato: quello che è stato realizzato dall’LNTS (Laboratori Nuove Tecologie Strumenti, UF Laboratori, Roma1) è una tessera del progetto STRADIUM (ASI), e fa tesoro dell’esperienza acquisita nella progettazione degli alimentatori del progetto PEGASO [Iarocci et al., 2008]. Nato per l’uso in stratosfera, l’alimentatore si presta benissimo all’uso in stazioni geofisiche remote. L’alimentatore accetta tre pannelli solari in ingresso ed utilizza due batterie di elementi Sn-Pb tenendo conto della variazione delle caratteristiche di carica con la temperatura. L’intervallo di temperatura di funzionamento, batterie comprese, va da –50 a + 60°C. La pressione di esercizio va da 1 bar a 5 mbar (dal livello del mare a 35 Km). Questi valori sono stati verificati sul prototipo, batterie comprese, in camera termovuoto. Le pagine che seguono sono quelle del manuale scritto a corredo dell’apparecchio: forniscono una descrizione fedele del principio di funzionamento e del dettaglio tecnico. Le seguenti figure fuori testo illustrano alcune delle fasi di costruzione e verifica del prototipo

Un generatore di impulso ad alta tensione per l'eccitazione di trasduttori piezoelettrici: un metodo per studiare la propagazione delle onde elastiche su campioni di rocce

Il dispositivo qui presentato è stato realizzato per lo studio della propagazione di onde elastiche in campioni di roccia [Wood A. W. Et al. 1955]. Mediante tale tecnica si riescono a determinare alcune caratteristiche fisiche delle rocce. Si tratta di un generatore di impulsi ad alta tensione, necessario per l’eccitazione di trasduttori piezoelettrici. La durata dell’impulso generato è di 1 s, l’ampiezza dell’ordine del kVolt. Il metodo utilizzato per effettuare la misura consiste nell’eccitare il trasduttore in trasmissione con un singolo impulso e quindi misurarne il tempo di volo con il trasduttore di ricezione. Il lavoro, oltre alla descrizione dello strumento, mostra alcuni esperimenti condotti su campioni di alluminio e diversi tipi di roccia. Tali esperimenti si sono resi necessari sia per il collaudo dello strumento che per la messa a punto del metodo