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Mardi 13 décembre 2016-14:00

Unveiling quantum correlations in many-body systems.

Irénée Frérot (ENS Lyon)

par Gabriel LeMarié - 13 décembre 2016

To quantify, compute and measure quantum coherence and many-body entanglement in extended quantum systems represents a formidable challenge. In this talk, I focus on systems at thermal equilibrium, and introduce the generic concept of "Quantum Variance" of an observable (as the difference between the total variance and the static susceptibility). By definition, it is directly accessible to experiments. I will explain that the Quantum Variance is deeply rooted in the path integral formulation of quantum statistical mechanics (as it quantifies the variance in imaginary time). I will show that the Quantum Variance provides both a lower and upper bound to the Wigner-Yanase skew information and to the Quantum Fisher information (two widely accepted measures of quantum coherence and quantum correlations). Discussing calculations on a model of hardcore bosons, I will then extend the concept to the "Quantum Correlation Function", exhibiting a finite "Entanglement depth" even when the usual correlation function decays algebraically at long distance (in the superfluid phase). Finally, I will show how the Quantum Variance reveals the "Quantum critical fan" in the vicinity of a quantum phase transition.

Post-scriptum :

contact : N. Laflorencie