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TT: Fachverband Tiefe Temperaturen

TT 3: TR: Fluctuations and Noise

TT 3.4: Vortrag

Montag, 22. März 2010, 11:00–11:15, H20

Quasiprobability and weak measurement of current noise in a quantum point contact — •Adam Bednorz^1,2 and Wolfgang Belzig¹ — ¹Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Deutschland — ²Institute of Theoretical Physics, University of Warsaw, Hoza 69, 00-681 Warsaw, Poland

The charge flow (counting statistics) through mesoscopic junctions is well described by Bernoulli statistics in the long time (low frequency) limit [1] which follows from a projective detection model. The problem becomes more complicated and interesting, when considering the measurement of noncommuting observables, e.g. current and phase or time-resolved current [2]. The latter case can be resolved in terms of the weak measurement [3]. The idea is similar to the concept of weak values [4]. We show that the outcome of the weak measurement can be interpreted in terms of a quasiprobability. Namely, the total probability distribution of the measured values of observables is a convolution of a large, white, Gaussian detection noise and a quasiprobability (independent of the detector). We show that the quasiprobability can take negative values. The negative quasiprobability can be measured, if the Gaussian noise is subtracted, by a measurement of the fourth cumulant at high frequencies.

[1] G.B. Lesovik and L.S. Levitov, Phys. Rev. Lett. 72, 538 (1994).
[2] W. Belzig and Y.V. Nazarov, Phys. Rev. Lett. 87, 197006 (2001).
[3] A. Bednorz and W. Belzig, Phys. Rev. Lett. 101, 206803 (2008).
[4] Y. Aharonov, D.Z. Albert and L. Vaidman, Phys. Rev. Lett. 60, 1351 (1988).