681 research outputs found
Non-ergodic phenomena in many-body quantum systems
No full textThe assumption of ergodicity is the cornerstone of conventional thermodynamics, connecting the equilibrium properties of macroscopic systems to the chaotic nature of the underlying microscopic dynamics, which eventuates in thermalization and the scrambling of information contained in any generic initial condition. The modern understanding of ergodicity in a quantum mechanical framework is encapsulated in the so-called eigenstate thermalization hypothesis, which asserts that thermalization of an isolated quantum system is a manifestation of the random-like character of individual eigenstates in the bulk of the spectrum of the system's Hamiltonian.
In this work, we consider two major exceptions to the rule of generic thermalization in interacting many-body quantum systems: many-body localization, and quantum spin glasses. In the first part, we debate the possibility of localization in a system endowed with a non-Abelian symmetry. We show that, in line with proposed theoretical arguments, such a system is probably delocalized in the thermodynamic limit, but the ergodization length scale is anomalously large, explaining the non-ergodic behavior observed in previous experimental and numerical works. A crucial feature of this system is the quasi-tensor-network nature of its eigenstates, which is dictated by the presence of nontrivial symmetry multiplets. As a consequence, ergodicity may only be restored by extensively large cascades of resonating spins, explaining the system's resistance to delocalization. In the second part, we study the effects of non-ergodic behavior in glassy systems in relation to the possibility of speeding up classical algorithms via quantum resources, namely tunneling across tall free energy barriers. First, we define a pseudo-tunneling event in classical diffusion Monte Carlo (DMC) and characterize the corresponding tunneling rate. Our findings suggest that DMC is very efficient at tunneling in stoquastic problems even in the presence of frustrated couplings, asymptotically outperforming incoherent quantum tunneling. We also analyze in detail the impact of importance sampling, finding that it does not alter the scaling. Next, we study the so-called population transfer (PT) algorithm applied to the problem of energy matching in combinatorial problems. After summarizing some known results on a simpler model, we take the quantum random energy model as a testbed for a thorough, model-agnostic numerical characterization of the algorithm, including parameter setting and quality assessment. From the accessible system sizes, we observe no meaningful asymptotic speedup, but argue in favor of a better performance in more realistic energy landscapes
Lettera di Alessandra
No full textUn ritratto critico dell'opera di Alessandra Carnaroli, autrice fra le più apprezzate delle ultime generazioni della poesia di ricerca. La sezione a lei dedicata, nel numero della rivista, contiene inoltre saggi di Cecilia Bello Minciacchi, Andrea Cortellessa, e Ivan Schiavone; e vari inediti dell'autrice. Il saggio è pubblicato con lo pseudonimo di Tommaso Ottonieri.A critical portrait of the work of Alessandra Carnaroli, author of the most appreciated in the latest generations of italian research poetry. Published under the pseudonym Tommaso Ottonieri
Understanding quantum tunneling using diffusion Monte Carlo simulations
No full textIn simple ferromagnetic quantum Ising models characterized by an effective double-well energy landscape the characteristic tunneling time of path-integral Monte Carlo (PIMC) simulations has been shown to scale as the incoherent quantum-tunneling time, i.e., as 1/Delta(2), where Delta is the tunneling gap. Since incoherent quantum tunneling is employed by quantum annealers (QAs) to solve optimization problems, this result suggests that there is no quantum advantage in using QAs with respect to quantum Monte Carlo (QMC) simulations. A counterexample is the recently introduced shamrock model (Andriyash and Amin, arXiv: 1703.09277), where topological obstructions cause an exponential slowdown of the PIMC tunneling dynamics with respect to incoherent quantum tunneling, leaving open the possibility for potential quantum speedup, even for stoquastic models. In this work we investigate the tunneling time of projective QMC simulations based on the diffusion Monte Carlo (DMC) algorithm without guiding functions, showing that it scales as 1/Delta, i.e., even more favorably than the incoherent quantum-tunneling time, both in a simple ferromagnetic system and in the more challenging shamrock model. However, a careful comparison between the DMC ground-state energies and the exact solution available for the transverse-field Ising chain indicates an exponential scaling of the computational cost required to keep a fixed relative error as the system size increases
Editorial: Dysmetabolism, obesity, and inflammation: Three prominent actors in the drama of major neuropsychiatric disorders
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Una facezia di Poggio nell'«Epirota» di Tommaso de Mezzo
No full textPrinted in 1483, Tommaso de Mezzo’s «Epirota» belongs to the second time of the
latin humanistic comedy of the Quattrocento, characterized by a strictly imitation of
Plaute (and also of Terence), more strong than in the texts of the first half of the century.
The first section of this paper presents Tommaso de Mezzo’s life and works, and plot,
types and subjects of «Epirota». The second part of the article offers the analysis of some
scenes of the comedy, in which the author clearly employs one of Bracciolini’s «Facetiae»
Nel giro del sangue, su Tommaso Ottonieri
No full textIl saggio analizza l'opera di Tommaso Ottonieri "Le strade che portano al Fùcino" mettendone in evidenza l'infrazione dei generi letterari, l'originalità dei nuclei poetici e di quelli narrativi, oltre alla stratificazione plurilinguistica che è cifra stilistica e allegorica dell'opera. Il saggio, inoltre, individua i rapporti di quest'opera di Ottonieri con le immagini visive e con la cultura musicale coeva e rintraccia anche rapporti intertestuali con precedenti opere poetiche, narrative e saggistiche dell'autore.The essay analyzes the work of Tommaso Ottonieri "Le strade che portano al Fùcino" highlighting the infringement of literary genres, the originality of poetic and narrative nuclei, in addition to the plurilingual stratification which is the stylistic and allegorical cipher of the Opera. Furthermore, the essay identifies the relationships of this work by Ottonieri with visual images and contemporary musical culture and also traces intertextual relationships with previous poetic works, narratives and essays by the author
L’olio in un aneddoto dalle biografie di Cesare (Plut. Caes. 17, 9–10 e Suet. Iul. 53)
No full textThe paper discusses a debated anecdote on Julius Caesar that Plutarch and Suetonius probably derived from the writer and politician Gaius Oppius. By examining some hitherto neglected Latin agronomic and gastronomic sources, the author provides some examples of olea condita used for culinary purposes and reassesses the interpretation of the anecdote
APROXIMACIÓN AL ESTUDIO DE LA LENGUA POÉTICA DE TOMMASO STIGLIANI
No full textEn este estudio hemos querido trazar un primer acercamiento al estudio de la lengua poética del autor italiano Tommaso Stigliani y lo hemos hecho analizando su mayor obra, Il Mondo Nuovo (1628), poema épico sobre el descubrimiento de América. Hemos analizado los principales fenómenos de la ortografía, la fonética, la morfología, la sintaxis y el léxico que aparecen en el texto, teniendo en cuenta la norma lingüística del siglo XVII y las opiniones y teorías de los principales lingüistas de la época. Con este estudio, por tanto, ofrecemos un acercamiento a la concepción de lengua poética que Tommaso Stigliani, a través de su poema y de sus escritos teóricos, puso de manifiesto a lo largo de su carrera literaria.
Abstract
In this study, we have attempted to make inroads into the study of the poetic language of the Italian author, Tommaso Stigliani, analysing his principal work, Il Mondo Nuovo (1628), an epic poem on the discovery of America. We have examined the main phenomena of orthography, phonetics, morphology, syntax and lexicon that appear in the text, taking into account the linguistic norms of the 17th century, as well as the opinions and theories of the major linguistic experts of that period. Our study, therefore, gives an insight into Tommaso Stigliani’s conception of poetic language, which, through his poem and his theoretical writings, he maintained for the duration of his literary career
Aproximación al estudio de la lengua poética de Tommaso Stigliani
No full textIn this study, we have attempted to make inroads into the study of the poetic language of the Italian author, Tommaso Stigliani, analysing his principal work, Il Mondo Nuovo (1628), an epic poem on the discovery of America. We have examined the main phenomena of orthography, phonetics, morphology, syntax and lexicon that appear in the text, taking into account the linguistic norms of the 17th century, as well as the opinions and theories of the major linguistic experts of that period. Our study, therefore, gives an insight into Tommaso Stigliani¿s conception of poetic language, which, through his poem and his theoretical writings, he maintained for the duration of his literary careerEn este estudio hemos querido trazar un primer acercamiento al estudio de la lengua poética del autor italiano Tommaso Stigliani y lo hemos hecho analizando su mayor obra, Il Mondo Nuovo (1628), poema épico sobre el descubrimiento de América. Hemos analizado los principales fenómenos de la ortografía, la fonética, la morfología, la sintaxis y el léxico que aparecen en el texto, teniendo en cuenta la norma lingüística del siglo XVII y las opiniones y teorías de los principales lingüistas de la época. Con este estudio, por tanto, ofrecemos un acercamiento a la concepción de lengua poética que Tommaso Stigliani, a través de su poema y de sus escritos teóricos, puso de manifiesto a lo largo de su carrera literaria
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