Vendredi 03 mai 2013 à 14h15

Auditoire Stueckelberg, Ecole de Physique

### Weak Measurements in Quantum Transport and Beyond

**Wolfgang Belzig**, University of Konstanz

###### The difficulty in measuring non-commuting quantum mechanical observables is one of the most fascinating consequences of the quantum mechanical postulates, relevant for correlation measurements of the electric current [1]. Hence, the investigation of quantum measurement and projection is a fundamentally interesting topic. We study the concept of weak measurement of non-commuting observables using a quasiprobabilistic description [2] relevant for mesoscopic transport experiments, resembling the Wigner function and other quasiprobabilities [3]. The negativity of a quasiprobability can be tested by violation of classically derived inequalities. We discuss as first examples of such so-called quantum paradoxes an inequality violated by high-frequency fourth-order current cumulants in the quantum regime for experimentally feasible parameters [4]. As second example we show how to detect nonlocal quantum correlations (entanglement) in mesoscopic junctions, which do not permit detection of single events [5]. [1] A. Bednorz and W. Belzig, Phys. Rev. Lett. 101, 206803 (2008). [2] A. Bednorz and W. Belzig, Phys. Rev. B 81, 125112 (2010). [3] A. Bednorz, C. Bruder, B. Reulet and W. Belzig, arxiv:1211.6056. [4] A. Bednorz and W. Belzig, Phys. Rev. Lett. 105, 106803 (2010). [5] A. Bednorz and W. Belzig, Phys. Rev. B 83, 125304 (2011).