CPM Seminar

Current fluctuations in conductors:
beyond noise

Bertrand Reulet

Département de Physique
Université de Sherbrooke

In usual “noise” measurements, one detects the variance of current fluctuations i(f) around a given frequency f, i.e. <i²(f)>. We will present new experiments which address questions that go beyond this:

• Noise dynamics - he time-dependent response of the average current to an ac voltage is given by the complex impedance of the sample; what describes the time-dependent response of the noise? We describe an experiment on a tunnel junction in the quantum regime, when the frequency is larger than the applied voltage and the temperature.
• Third cumulant in the quantum regime - The current fluctuations in a system out of equilibrium are asymmetric. This implies the existence of a non-zero third cumulant <i³>, which has been observed at zero frequency. What is it in the quantum regime, when the noise comes from the zero point motion of electrons? This problem is strongly related to that of non commutativity of operators in quantum mechanics.
• Higher order cumulants in a complex system Can one probe the statistics of a complex system simply by detecting and analyzing its fluctuations? We show measurements of high order cumulants <iⁿ> in an avalanche diode from which the power law distribution of the avalanche size can be deduced.