Adiabatic quantum dynamics of a random Ising chain across its quantum critical point

We present here our study of the adiabatic quantum dynamics of a random Ising chain across its quantum critical point. The model investigated is an Ising chain in a transverse field with disorder present both in the exchange coupling and in the transverse field. The transverse field term is proportional to a function $\Gamma(t)$ which, as in the Kibble-Zurek mechanism, is linearly reduced to zero in time with a rate $\tau^{-1}$, $\Gamma(t)=-t/\tau$, starting at $t=-\infty$ from the quantum disordered phase ($\Gamma=\infty$) and ending at $t=0$ in the classical ferromagnetic phase ($\Gamma=0$). We first analyze the distribution of the gaps -- occurring at the critical point $\Gamma_c=1$ -- which are relevant for breaking the adiabaticity of the dynamics. We then present extensive numerical simulations for the residual energy $E_{\rm res}$ and density of defects $\rho_k$ at the end of the annealing, as a function of the annealing inverse rate $\tau$. %for different lenghts of the chain. Both the average $E_{\rm res}(\tau)$ and $\rho_k(\tau)$ are found to behave logarithmically for large $\tau$, but with different exponents, $[E_{\rm res}(\tau)/L]_{\rm av}\sim 1/\ln^{\zeta}(\tau)$ with $\zeta\approx 3.4$, and $[\rho_k(\tau)]_{\rm av}\sim 1/\ln^{2}(\tau)$. We propose a mechanism for $1/\ln^2{\tau}$-behavior of $[\rho_k]_{\rm av}$ based on the Landau-Zener tunneling theory and on a Fisher's type real-space renormalization group analysis of the relevant gaps. The model proposed shows therefore a paradigmatic example of how an adiabatic quantum computation can become very slow when disorder is at play, even in absence of any source of frustration.Comment: 10 pages, 11 figures; v2: added references, published versio

Cloning transformations in spin networks without external control

In this paper we present an approach to quantum cloning with unmodulated spin networks. The cloner is realized by a proper design of the network and a choice of the coupling between the qubits. We show that in the case of phase covariant cloner the XY coupling gives the best results. In the 1->2 cloning we find that the value for the fidelity of the optimal cloner is achieved, and values comparable to the optimal ones in the general N->M case can be attained. If a suitable set of network symmetries are satisfied, the output fidelity of the clones does not depend on the specific choice of the graph. We show that spin network cloning is robust against the presence of static imperfections. Moreover, in the presence of noise, it outperforms the conventional approach. In this case the fidelity exceeds the corresponding value obtained by quantum gates even for a very small amount of noise. Furthermore we show how to use this method to clone qutrits and qudits. By means of the Heisenberg coupling it is also possible to implement the universal cloner although in this case the fidelity is 10% off that of the optimal cloner.Comment: 12 pages, 13 figures, published versio

From perfect to fractal transmission in spin chains

Perfect state transfer is possible in modulated spin chains, imperfections however are likely to corrupt the state transfer. We study the robustness of this quantum communication protocol in the presence of disorder both in the exchange couplings between the spins and in the local magnetic field. The degradation of the fidelity can be suitably expressed, as a function of the level of imperfection and the length of the chain, in a scaling form. In addition the time signal of fidelity becomes fractal. We further characterize the state transfer by analyzing the spectral properties of the Hamiltonian of the spin chain.Comment: 8 pages, 10 figures, published versio

Il percorso di chiusura degli Opg e le nuove Rems: stato dell’arte e prospettive future

La complessa vicenda degli Ospedali Psichiatrici Giudiziari (OPG), a fronte delle evidenti criticità di tali luoghi per l’internamentodegli autori di reato non imputabili per infermità mentale e socialmente pericolosi, ha portato nel 2015 alla loroprogressiva e definitiva chiusura. Contestualmente, il legislatore ha disposto la loro sostituzione con le “Residenze per l’Esecuzionedelle Misure di Sicurezza” (REMS), quali strutture di carattere prettamente terapeutico, improntate sui principi dellasanitarizzazione e territorializzazione del trattamento. Il presente contributo intende osservare il risultato di questo tortuosoe significativo percorso di superamento e trasformazione della misura di sicurezza, conclusosi ufficialmente nella primaveradel 2017, con il cessato funzionamento dell’ultimo OPG, e con la realizzazione sul territorio regionale delle nuove REMS

Nuove prospettive di ricerca in materia di atti persecutori: il fenomeno del cyberstalking

Electronic stalking is a frequent phenomenon worthy of scientific and social interest, closely related to the constant and exponential progress of technology. These types of conducts are defined by literature as cyberstalking, and even if it has no one universally agreed upon definition, it is considered as the use of the internet, email, or other electronic devices to stalk another person. Today, it seems to be a serious problem that will become more complex and dangerous as more people take advantage of the Internet and other telecommunications technologies. An easier and faster access to cyberspace also means a greater risk of incorrect use or misuse of the medium, in order to attack or intrude into the lives of others, taking advantage of anonymity and of the absence of limitations present in a real context.Even if empirical works on cyberstalking are still few, the existing data gives evidence of its quantitative importance and of a lack of awareness. The Report published by the US Attorney General in 1999, estimated the presence in the country of about 475.000 victims of cyberstalking each year, while police reported the presence in 20% of cases of reported harassment forms of abuse through Internet and technological means in general. In a perspective of prevention and intervention, investigating and implementing the existing research on the phenomenon seem essential, taking into account that such harassment are rarely limited to the virtual world, being able to produce effects often similar if not more severe than those produced by offline stalking.Le molestie telematiche rappresentano un fenomeno frequente e degno di interesse scientifico e sociale, strettamente correlato al costante ed esponenziale progredire della tecnologia. Queste tipologie di condotte sono definite dalla letteratura cyberstalking, intendendo con questo termine, pur in assenza di una definizione univoca, l’utilizzo di internet, email o di altri dispositivi elettronici per molestare un’altra persona. Si tratta di una problematica rilevante, destinata a diventare sempre più complessa e pericolosa con l’aumento inarrestabile dell’utilizzo di Internet e delle tecnologie informatiche da parte di fasce sempre più ampie di popolazione. Un più facile e veloce accesso al cyberspazio comporta anche un maggior rischio di utilizzo erroneo o di abusi del mezzo, al fine di aggredire o intromettersi nella vita di altre persone, approfittando dell’anonimato e dell’assenza dei limiti presenti in un contesto reale.Sul piano della prevalenza, seppur numericamente limitati, gli studi empirici esistenti dimostrano una non trascurabile incidenza del fenomeno e una prevalente mancanza di consapevolezza da parte della popolazione generale. Il Report pubblicato dall’Attorney General statunitense nel 1999, stimava la presenza nel paese di circa 475.000 vittime di cyberstalking all’anno, mentre la Polizia riferiva la presenza nel 20% dei casi di molestie rilevati di forme di abuso via Internet e mezzi tecnologici in genere In un’ottica, quindi, di prevenzione e di intervento sembra indispensabile approfondire e implementare la ricerca sul fenomeno, tenuto conto del fatto che raramente queste molestie restano limitate al mondo virtuale, essendo in grado di produrre effetti reali talvolta analoghi se non più gravi rispetto a quelli dello stalking offline

Decentralized Voltage Optimization Based on the Auxiliary Problem Principle in Distribution Networks with DERs

This paper addresses the problem of optimizing the voltage profile of radially-operated distribution systems by acting on the active and reactive powers provided by distributed energy resources (DERs). A novel voltage optimization procedure is proposed by adopting a decentralized control strategy. To this aim, a centralized voltage optimization problem (VOP), minimizing the distance of all the nodal voltages from their reference values, is firstly formulated as a strictly-convex quadratic program. Then, the centralized VOP is rewritten by partitioning the network into voltage control zones (VCZs) with pilot nodes. To overcome the lack of strictly convexity determined by the reduction to the pilot nodes, the dual centralized VOP working on the augmented Lagrangian function is reformulated and iteratively solved by the method of multipliers. Finally, a fully-distributed VOP solution is obtained by applying a distributed algorithm based on the auxiliary problem principle, which allows for solving in each VCZ a quadratic programming problem of small dimension and to drive the VCZ solutions toward the overall optimum by an iterative coordination process that requires to exchange among the VCZs only scalar values. The effectiveness and feasibility of the proposed method have been demonstrated via numerical tests on the IEEE 123-bus system

Stochastic dynamics beyond the weak coupling limit: thermalization

We discuss the structure and asymptotic long-time properties of coupled equations for the moments of a Brownian particle's momentum derived microscopically beyond the lowest approximation in the weak coupling parameter. Generalized fluctuation-dissipation relations are derived and shown to ensure convergence to thermal equilibrium at any order of perturbation theory.Comment: 6+ page

Entanglement production by quantum error correction in the presence of correlated environment

We analyze the effect of a quantum error correcting code on the entanglement of encoded logical qubits in the presence of a dephasing interaction with a correlated environment. Such correlated reservoir introduces entanglement between physical qubits. We show that for short times the quantum error correction interprets such entanglement as errors and suppresses it. However for longer time, although quantum error correction is no longer able to correct errors, it enhances the rate of entanglement production due to the interaction with the environment.Comment: 7 pages, 3 figures, published versio

Shortcut to Adiabaticity in the Lipkin-Meshkov-Glick Model

We study transitionless quantum driving in an infinite-range many-body system described by the Lipkin- Meshkov-Glick model. Despite the correlation length being always infinite the closing of the gap at the critical point makes the driving Hamiltonian of increasing complexity also in this case. To this aim we develop a hybrid strategy combining a shortcut to adiabaticity and optimal control that allows us to achieve remarkably good performance in suppressing the defect production across the phase transition

Stalking e mass media

Unanimously the international research recognizes the fundamental role of the media in the affirmation of the phenomenon of stalking in the U.S.A., beginning from its same labelling. Star-stalking cases, accomplice the notoriety of the victims, has represented a starting point of the media interest that next has allowed to discover the prevalence of these conducts among the general population. The progressive social visibility of the phenomenon, promoted through the media, has produced the recognition of the stalking as a criminal problem, pushing the common law countries legislators to the creation of specific anti-stalking legislation. The research intends to investigate the role of the Italian media in the process of social and juridical affirmation of stalking, ended with the approval of the DL 23 February 2009 n.11 and the consequent introduction of the article 612-bis c.p. “Atti persecutori”. The relationship between stalking and media in Italy, the relevance and the importance of the progressive change of social visibility, considering the particular way of working of the media, has been investigated through the collection and the analysis of the articles published since 1992 to November 2009 on Corriere della Sera, main national diffusion daily paper, and on Quotidiano.net, that brings the news of different local journalistic headings (Resto del Carlino, La Nazione, Il Giorno). The 506 selected articles, 293 published on Corriere della Sera (57,9%) e 213 on Quotidiano.net (42,1%), have globally been submitted to a first level of analysis based on the context of the article, the typology of content, the ability of recognition and the language used to define the behaviors. The second level of analysis has involved only news articles, studied through valutative analysis grids about victims, stalkers, typology of relationship, star-stalking cases and presence of violent behaviors. The typology of article mostly diffused on newspapers results to be the chronicle, that represents the 84,6% of the total. Popular and/or scientific ones represent the 7,7% of the total as medium value of the period, but their diffusion results constant only starting from 2001. The political news are the 5,7% of the total and they are recognisable starting from 2006. The use of the term stalking appears constantly among the media from 2002 with a progressive increasement in the next years (44% in 2007; 52,1% in 2008; 94% in 2009), representing by now the defining term of the phenomenon. Among 449 victims, found from 1992 to 2009, 372 (82,9%) are women. Among 440 stalker, found from 1992 to 2009, 84,3% are men and only 15,7% women. More than half of the stalkers was an ex-partner of the victim (51,2%). The stalker results to be an acquaintance in 24,3% of the cases and a perfect stranger in 24,5%. On 428 chronicle articles selected since 1992 to 2009, more than the half (51,4%) describes stories of stalking connotated by violent behaviors: physical injuries, assaults (also sexual), tempted and consumed homicides.La ricerca internazionale concordemente riconosce il ruolo determinante dei media nel percorso di affermazione del fenomeno dello stalking in U.S.A., a partire dal suo stesso “etichettamento”. I casi di star-stalking, complice la notorietà delle vittime, hanno rappresentato un iniziale polarizzatore mediatico che ha successivamente permesso la riconoscibilità delle condotte di molestie a danno della popolazione comune. La progressiva visibilità sociale del fenomeno, promossa per via mediale, ha poi determinato il riconoscimento dello stalking quale problematica di rilevanza penale, spingendo il legislatore anglosassone all’emanazione di apposite leggi anti-stalking. Alla luce di queste considerazioni, lo studio qui presentato intende indagare il ruolo dei media italiani nel processo di affermazione sociale e giuridica dello stalking, culminato con l’approvazione del DL 23 febbraio 2009 n.11 e la conseguente introduzione dell’art. 612-bis c.p. “Atti persecutori”. Alla luce di queste considerazioni, lo studio qui presentato intende indagare il ruolo dei media italiani nel processo di affermazione sociale e giuridica dello stalking, culminato con l’approvazione del DL 23 febbraio 2009 n.11 e la conseguente introduzione dell’art. 612-bis c.p. “Atti persecutori”. Il rapporto tra stalking e mass media in Italia, l’entità e l’importanza del progressivo mutamento della sua osservabilità sociale, anche, e soprattutto, alla luce del peculiare funzionamento dei media è stato indagato mediante la raccolta e l’analisi degli articoli pubblicati dal gennaio 1992 all’aprile 2009 sul Corriere della Sera, principale quotidiano a diffusione nazionale, e su Quotidiano.net, che riporta le notizie di diverse testate giornalistiche a diffusione locale (Resto del Carlino, La Nazione, Il Giorno). I 506 articoli selezionati, 293 pubblicati sul Corriere della Sera (pari al 57,9%) e 213 su Quotidiano.net (pari al 42,1%), sono stati globalmente sottoposti a un primo livello di analisi basato sul contesto dell’articolo, ovvero la tipologia di contenuto, la capacità di riconoscimento e il linguaggio utilizzato per la definizione delle condotte. Il secondo livello di analisi ha coinvolto i soli articoli di cronaca, sottoposti a griglie valutative riguardanti le vittime, gli stalker, la tipologia di relazione intercorrente tra gli stessi, i casi di star-stalking e la ricorrenza di condotte violente. La tipologia di articolo maggiormente diffusa sui quotidiani risulta essere la cronaca, che rappresenta l’84,6% del totale.Gli articoli di tipo divulgativo e/o scientifico rappresentano il 7,7% del totale quale media del periodo, ma la loro diffusione sui quotidiani risulta costante solo a partire dal 2001. Le notizie di tipo politico rappresentano il 5,7% del totale e sono rintracciabili solo a partire dal 2006. L’uso del termine stalking da parte dei media risulta costante a partire dal 2002 con un aumento progressivo negli anni successivi (44% nel 2007; 52,1% nel 2008; 94% nel 2009) tanto da rappresentare, ormai, il termine di riferimento del fenomeno. Su 449 vittime individuate dal 1992 al 2009, ben 372 (pari all’82,9%) sono donne. Su 440 stalker individuati tra il 1992 e il 2009 l’84,3% sono uomini e solo il 15,7% donne. Più della metà degli stalker era un ex-partner della vittima (51,2%). Lo stalker risulta essere un conoscente della vittima nel 24,3% dei casi e un perfetto sconosciuto nel 24,5%. Su 428 articoli di cronaca selezionati dal 1992 al 2009, più della metà (51,4%) riportano vicende di stalking marcatamente connotate da condotte violente: percosse, lesioni personali, aggressioni (anche sessuali), omicidi tentati e consumati