1,720,964 research outputs found
Mitigating crosstalk errors by randomized compiling: Simulation of the BCS model on a superconducting quantum computer
No full textWe develop and apply an extension of the randomized compiling (RC) protocol that includes a special treatment of neighboring qubits and dramatically reduces crosstalk effects caused by the application of faulty gates on superconducting qubits in IBMQ quantum computers (ibm_lagos and ibmq_ehningen). Crosstalk errors, stemming from controlled- NOT ( CNOT) two-qubit gates, are a crucial source of errors on numerous quantum computing platforms. For the IBMQ machines, their effect on the performance of a given quantum computation is often overlooked. Our RC protocol turns coherent noise due to crosstalk into a depolarizing noise channel that can then be treated using established error mitigation schemes, such as noise estimation circuits. We apply our approach to the quantum simulation of the nonequilibrium dynamics of the Bardeen-Cooper-Schrieffer (BCS) Hamiltonian for superconductivity, a particularly challenging model to simulate on quantum hardware because of the long-range interaction of Cooper pairs. With 135 CNOT gates, we work in a regime where crosstalk, as opposed to either Trotterization or qubit decoherence, dominates the error. Our twirling of neighboring qubits is shown to dramatically improve the noise estimation protocol without the need to add new qubits or circuits and allows for a quantitative simulation of the BCS mode
Dynamique hors d’équilibre et thermalisation des gaz de Bose désordonnés en interaction faible
No full textThis thesis manuscript is devoted to different aspects of the non-equilibrium dynamics of a moving two-dimensional ultra-cold Bose gas, under the simultaneous action of a spatially disordered potential and interactions between particles. In the absence of interactions, the momentum distribution of the gas is the sum of two well-known components: a classical, diffusive background made of particles multiply scattered by the disorder, and a coherent backscattering interference peak (CBS peak), consequence of the weak localization phenomenon. In the presence of weak interactions, mean field simulations show that these two contributions evolve in time. This evolution is described by two coupled kinetic equations, which we derive using a microscopic quantum transport theory. These predict the destruction of the CBS peak by an effective dephasing mechanism, and the thermalization of the diffusive background. As the interaction strength increases, the effects of disorder become negligible, and the dynamics of the gas resembles that of a superfluid. In this regime, the gas quickly enters a so-called "pre-thermal" state: the spatial correlations g_1 decrease algebraically and propagate along a light cone, in accordance with theoretical predictions. Finally, at long times, our simulations describe the global evolution of the system towards a thermal equilibrium state, characterized by a Kosterlitz-Thouless transition separating a normal fluid state from a superfluid state. Some properties of this phase transition, resulting from the non-equilibrium evolution in the presence of disorder, are discussed.Ce manuscrit de thèse est consacré à différents aspects de la dynamique hors d’équilibre d’un gaz de Bose bi-dimensionnel ultra-froid en mouvement, sous l’action simultanée d’un potentiel spatialement désordonné et d’interactions entre particules. En l’absence d’interactions, la distribution des impulsions du gaz est la somme de deux composantes bien connues : un fond classique constitué de particules multiplement diffusées par le désordre, ainsi qu’un pic interférentiel de rétro-diffusion cohérente (pic CBS, en anglais), conséquence du phénomène de localisation faible. En présence d’interactions faibles, les simulations de champ moyen montrent que ces deux contributions évoluent dans le temps. Cette évolution est décrite par deux équations cinétiques couplées, que nous dérivons au moyen d’une théorie de transport quantique microscopique. Ces dernières décrivent la destruction du pic CBS par un mécanisme de déphasage, et la thermalisation du fond diffusif. Lorsque la force des interactions augmente, les effets du désordre deviennent négligeables, et la dynamique du gaz ressemble à celle d’un superfluide. Dans ce régime, le gaz entre rapidement dans un état dit «pré-thermal» : les corrélations spatiales g_1 décroissent algébriquement et se propagent en suivant un cône de lumière, conformément aux prédictions théoriques. Enfin, aux temps longs, nos simulations décrivent l’évolution globale du système vers un état d’équilibre thermal, caractérisé par une transition Kosterlitz-Thouless séparant un état de fluide normal d’un état superfluide. Quelques propriétés de cette transition de phase, issue de l’évolution hors d’équilibre en présence de désordre sont discutées
Out-of-equilibrium dynamics and thermalization of weakly interacting disordered Bose gases
No full textCe manuscrit de thèse est consacré à différents aspects de la dynamique hors d’équilibre d’un gaz de Bose bi-dimensionnel ultra-froid en mouvement, sous l’action simultanée d’un potentiel spatialement désordonné et d’interactions entre particules. En l’absence d’interactions, la distribution des impulsions du gaz est la somme de deux composantes bien connues : un fond classique constitué de particules multiplement diffusées par le désordre, ainsi qu’un pic interférentiel de rétro-diffusion cohérente (pic CBS, en anglais), conséquence du phénomène de localisation faible. En présence d’interactions faibles, les simulations de champ moyen montrent que ces deux contributions évoluent dans le temps. Cette évolution est décrite par deux équations cinétiques couplées, que nous dérivons au moyen d’une théorie de transport quantique microscopique. Ces dernières décrivent la destruction du pic CBS par un mécanisme de déphasage, et la thermalisation du fond diffusif. Lorsque la force des interactions augmente, les effets du désordre deviennent négligeables, et la dynamique du gaz ressemble à celle d’un superfluide. Dans ce régime, le gaz entre rapidement dans un état dit «pré-thermal» : les corrélations spatiales g_1 décroissent algébriquement et se propagent en suivant un cône de lumière, conformément aux prédictions théoriques. Enfin, aux temps longs, nos simulations décrivent l’évolution globale du système vers un état d’équilibre thermal, caractérisé par une transition Kosterlitz-Thouless séparant un état de fluide normal d’un état superfluide. Quelques propriétés de cette transition de phase, issue de l’évolution hors d’équilibre en présence de désordre sont discutées.This thesis manuscript is devoted to different aspects of the non-equilibrium dynamics of a moving two-dimensional ultra-cold Bose gas, under the simultaneous action of a spatially disordered potential and interactions between particles. In the absence of interactions, the momentum distribution of the gas is the sum of two well-known components: a classical, diffusive background made of particles multiply scattered by the disorder, and a coherent backscattering interference peak (CBS peak), consequence of the weak localization phenomenon. In the presence of weak interactions, mean field simulations show that these two contributions evolve in time. This evolution is described by two coupled kinetic equations, which we derive using a microscopic quantum transport theory. These predict the destruction of the CBS peak by an effective dephasing mechanism, and the thermalization of the diffusive background. As the interaction strength increases, the effects of disorder become negligible, and the dynamics of the gas resembles that of a superfluid. In this regime, the gas quickly enters a so-called "pre-thermal" state: the spatial correlations g_1 decrease algebraically and propagate along a light cone, in accordance with theoretical predictions. Finally, at long times, our simulations describe the global evolution of the system towards a thermal equilibrium state, characterized by a Kosterlitz-Thouless transition separating a normal fluid state from a superfluid state. Some properties of this phase transition, resulting from the non-equilibrium evolution in the presence of disorder, are discussed
Noise tailoring and error mitigation for digital quantum simulations on NISQ devices
No full textInvited talk of Thibault Scoquart – Noise tailoring and error mitigation for digital quantum simulations on NISQ devices, held at Conference on Emergent Phenomena in Quantum Systems and Beyond in Santiago, Chile, from 31 March – 4 April 2025
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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