Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 21: Transport: Fluctuations and Noise

TT 21.6: Talk

Tuesday, March 24, 2009, 15:45–16:00, HSZ 304

Time-Resolved Counting Statistics for a Quantum Point Contact — •Adam Bednorz^1,2 and Wolfgang Belzig¹ — ¹Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany — ²Institute of Theoretical Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland

We show that the naive formulation of time-resolved full counting statistics fails for high frequencies and leads to results, which could be interpreted as negative probabilities. We propose to construct a properly time-ordered positive-operator-valued measure, that combines counting statistics with detector backaction parametrized by a characteristic time τ [1]. The standard counting statistics is recovered in long time limit. In high frequency limit, for a weak coupling between the system and detector, the generating functional of counting statistics gains an additional Gaussian white noise component, that saves the positivity of the probability. It agrees with experiments since otherwise at strong coupling the noise measurements would be considerably modified due to the detector backaction. Finally, we also show that with more than one detector these nonclassical correlations can be directly measured.

[1] A. Bednorz and W. Belzig, Phys. Rev. Lett. 101, 206803 (2008).