1,721,117 research outputs found
Quantum work and the thermodynamic cost of quantum measurements
Full text linkQuantum work is usually determined from two projective measurements of the energy at the beginning and at the end of a thermodynamic process. However, this paradigm cannot be considered thermodynamically consistent as it does not account for the thermodynamic cost of these measurements. To remedy this conceptual inconsistency we introduce a paradigm that relies only on the expected change of the average energy given the initial energy eigenbasis. In particular, we completely omit quantum measurements in the definition of quantum work, and hence quantum work is identified as a thermodynamic quantity of only the system. As main results we derive a modified quantum Jarzynski equality and a sharpened maximum work theorem in terms of the information free energy. A comparison of our results with the standard approach allows one to quantify the informational cost of projective measurements.Fil: Deffner, Sebastian. Los Alamos National Laboratory; Estados UnidosFil: Paz, Juan Pablo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Zurek, Wojciech H.. Los Alamos National Laboratory; Estados Unido
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
Geometric quantum speed limits: a case for Wigner phase space
No full textThe quantum speed limit is a fundamental upper bound on the speed of quantum evolution. However, the actual mathematical expression of this fundamental limit depends on the choice of a measure of distinguishability of quantum states. We show that quantum speed limits are qualitatively governed by the Schatten-p-norm of the generator of quantum dynamics. Since computing Schatten-p-norms can be mathematically involved, we then develop an alternative approach in Wigner phase space. We find that the quantum speed limit in Wigner space is fully equivalent to expressions in density operator space, but that the new bound is significantly easier to compute. Our results are illustrated for the parametric harmonic oscillator and for quantum Brownian motion.The author would like to thank Steve Campbell for insightful discussions. This work was supported by the US National Science Foundation under Grant No. CHE-1648973.https://iopscience.iop.org/article/10.1088/1367-2630/aa83d
Demonstration of entanglement assisted invariance on IBM’s quantum experience
No full textQuantum entanglement is among the most fundamental, yet from classical intuition also most surprising properties of the fully quantum nature of physical reality. We report several experiments performed on IBM's Quantum Experience demonstrating envariance – entanglement assisted invariance. Envariance is a recently discovered symmetry of composite quantum systems, which is at the foundational origin of physics and a quantum phenomenon of pure states. These very easily reproducible and freely accessible experiments on Quantum Experience provide simple tools to study the properties of envariance, and we illustrate this for several cases with “quantum universes” consisting of up to five qubits.The views expressed are those of the author and do not reflect the official policy or position of IBM or the IBM Quantum Experience team.https://www.cell.com/heliyon/fulltext/S2405-8440(17)31936-9?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2405844017319369%3Fshowall%3Dtru
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
FROM BLACK HOLES TO QUANTUM COMPUTERS: THE UNIVERSALITY OF INFORMATION DYNAMICS
No full textEstablishing a thermodynamic cost due to the manipulation and processing of information led to Landauer?s famous statement ?information is physical?. This thermodynamic view of information hints at a more fundamental underlying concept: the physicality of quantum information. However, a consistent framework to probe the physical nature of information in quantum systems is still lacking. In fact, in order to move closer towards a universal physical description of quantum information, clear links need to be made between the dynamics of quantum information and various physical concepts: emergence of classicality, environment-assisted invariance (envariance), work extraction, information processing in black holes and quantum computers, etc. This thesis presents research results for developing a fundamental understanding of major concepts in physics through information dynamics, with emphasis on a quantum thermodynamics perspective
Linear Computing and Thermodynamics
No full textA large part of computing deals with the doing, undoing, and reinterpretation of linear transformations on vector spaces. These operations are essential to the description of most physical phenomena, are a core part of machine learning, and also form the basic building blocks of quantum algorithms. The tendency of all things to evolve towards thermal equilibrium poses challenges for efficient and accurate computation, which often appear in the form of energy dissipation and errors caused by thermal noise. While thermal physics has provided some insights about physical limitations on computing, less is known about the particular considerations that apply to linear algebraic computations. Here, I study the application of thermodynamics to such problems, in both classical and quantum systems. Several new algorithms are given for linear algebra problems using specialized hardware, which have theoretical advantages over previously existing algorithms. Additionally, new bounds are proven for the energy cost of unitary transformations of quantum states, as well as for the efficiency of communication between quantum systems
Quantum Engines at the Frontiers of Physics
No full textThermodynamics was developed at the dawn of the industrial revolution to understand and optimize the new disruptive technology of the time, the steam engine. Emerging quantum technologies seem poised to usher in a new technological revolution based on the concept of the "quantum advantage" -- that quantum devices can harness non-classical correlations to outperform their classical counterparts. Practical and efficient implementation of such devices requires that we understand what energetic costs may be associated with utilizing these quantum resources, and how to minimize those costs. The developing field of quantum thermodynamics is uniquely poised to answer such questions. However, in order to understand how to extend the framework of thermodynamics to the quantum realm requires a well-established theoretical and practical framework. Heat engines serve as an ideal system for this task. In this dissertations, we comprehensively explore the quantum thermodynamics of indistinguishable particles guided by the analysis of quantum thermal machines
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