Search results for "Discord"

Discord of response

2014

The presence of quantum correlations in a quantum state is related to the state response to local unitary perturbations. Such response is quantified by the distance between the unperturbed and perturbed states, minimized with respect to suitably identified sets of local unitary operations. In order to be a bona fide measure of quantum correlations, the distance function must be chosen among those that are contractive under completely positive and trace preserving maps. The most relevant instances of such physically well behaved metrics include the trace, the Bures, and the Hellinger distance. To each of these metrics one can associate the corresponding discord of response, namely the trace,…

An entropic analysis of approximate quantum error correction

2013

The concept of entropy and the correct application of the Second Law of thermodynamics are essential in order to understand the reason why quantum error correction is thermodynamically possible and no violation of the Second Law occurs during its execution. We report in this work our first steps towards an entropic analysis extended to approximate quantum error correction (QEC). Special emphasis is devoted to the link among quantum state discrimination (QSD), quantum information gain, and quantum error correction in both the exact and approximate QEC scenarios.

Geometric measures of quantum correlations: characterization, quantification, and comparison by distances and operations

2016

We investigate and compare three distinguished geometric measures of bipartite quantum correlations that have been recently introduced in the literature: the geometric discord, the measurement-induced geometric discord, and the discord of response, each one defined according to three contractive distances on the set of quantum states, namely the trace, Bures, and Hellinger distances. We establish a set of exact algebraic relations and inequalities between the different measures. In particular, we show that the geometric discord and the discord of response based on the Hellinger distance are easy to compute analytically for all quantum states whenever the reference subsystem is a qubit. Thes…

Why a Quantum Tool in Classical Contexts?

2012

Les écrits autobiographiques de Sean O' Faolain: la voix concertante du soliste

2004

“Discord” aģents LU studiju informācijai

2021

Kvalifikācijas darba mērķis ir izstrādāt virtuālu komunikācijas aģentu, integrētu Discord vidē, ar kura palīdzību Latvijas Universitātes studējošie varētu ērti un ātri iegūt studiju informāciju, piemēram, lekciju grafiku konkrētai dienai un mācībspēku kontaktinformāciju, kā arī uzlabot patstāvīgā studiju darba plānošanu un saņemt atgādinājumus par gaidāmajiem pārbaudes darbiem. Aģenta darbība ir balstīta uz Discord komunikācijas platformas, kā arī uz Google servisiem Google Calendar un Google Sheets, kuros tiek glabāti studiju dati. Datu iegūšana un mainīšana tiek realizēta ar Google API piedāvātajām datu apmaiņas funkcijām, savukārt aģenta programmatūra tika izstrādāta izmantojot JavaScrip…

AN ASSOCIATION INDEX FOR RECTANGULAR CONTINGENCY TABLES WITH ORDERED/UNORDERED VARIABLES

2016

In a previous work, Mineo and Ruggieri (2005) introduce a new index to measure the association in square contingency tables; in this paper such an index is extended to rectangular tables, preserving the same properties. The considered domain includes all the contingency tables with equal n (the total number of observations), since the tables of maximum dependence, useful for computing the denominator of the proposed index, belong to it. The main findings, which prove the effectiveness of the proposed measure, are presented. In particular, the new measure assumes values in the range [-1,+1], taking value zero in tables with distributive independence and positive/negative values if associatio…

Dynamics and extraction of quantum discord in a multipartite open system

2011

We consider a multipartite system consisting of two noninteracting qubits each embedded in a single-mode leaky cavity, in turn connected to an external bosonic reservoir. Initially, we take the two qubits in an entangled state while the cavities and the reservoirs have zero photons. We investigate, in this six-partite quantum system, the transfer of quantum discord from the qubits to the cavities and reservoirs. We show that this transfer occurs also when the cavities are not entangled. Moreover, we discuss how quantum discord can be extracted from the cavities and transferred to distant systems by traveling leaking photons, using the input-output theory.

Characterizing and Quantifying Frustration in Quantum Many-Body Systems

2011

We present a general scheme for the study of frustration in quantum systems. We introduce a universal measure of frustration for arbitrary quantum systems and we relate it to a class of entanglement monotones via an exact inequality. If all the (pure) ground states of a given Hamiltonian saturate the inequality, then the system is said to be inequality saturating. We introduce sufficient conditions for a quantum spin system to be inequality saturating and confirm them with extensive numerical tests. These conditions provide a generalization to the quantum domain of the Toulouse criteria for classical frustration-free systems. The models satisfying these conditions can be reasonably identifi…

Persistence or change in leisure-time physical activity habits and waist gain during early adulthood: A twin-study

2014

Objective To determine the relationship between persistence or change in leisure-time physical activity habits and waist gain among young adults. Methods Population-based cohort study among 3383 Finnish twin individuals (1578 men) from five birth cohorts (1975-1979), who answered questionnaires at mean ages of 24.4 y (SD 0.9) and 33.9 y (SD 1.2), with reported self-measured waist circumference. Persistence or change in leisure-time physical activity habits was defined based on thirds of activity metabolic equivalent h/day during follow-up (mean 9.5 y; SD 0.7). Results Decreased activity was linked to greater waist gain compared to increased activity (3.6 cm, P < 0.001 for men; 3.1 cm, P < 0…