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Quantum shot noise in a tunnel junction : toward the dynamical control of tunneling processes - 22 september 2015 at 11 am

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Julien Gabelli - Laboratoire de Physique des solides - Université Paris-sud


In a typical quantum transport experiment, a nanostructure is placed at low temperature between two massive metallic contacts enabling electrical measurements with macroscopic apparatus. The quantum transport in the sample is perfectly described by a very simple idea : when the conductor is voltage biased, contacts emit electrons which are either transmitted or reflected. If quantum mechanics provides the transmission/reflection probabilities, it also induces strong correlations between successive attempts of the electron to cross the sample. Indeed, the wave-packet picture introduced by Martin and Landauer, tell us that Fermi statistics is responsible for the regular emission of electrons [1] and the absence of electronic noise for a perfectly transmitted conductor. The constant voltage source acts as a single electron turnstile and the average time between electrons emitted from the macroscopic contact is given by the time scale h/eV. It does not depend on the nature of the conductor but only on fundamental constants – the elementary charge e and the Planck constant h – and the voltage drop over the conductor. This characteristic time defines the quantum regime of dynamical electronic transport : at finite frequency hf >> kBT, the statistics of electrons crossing the conductor cannot be seen as a charge counting statistics problem anymore. It raises central questions about the quantum of the electron source : (i) What is defining its coherence ? (ii) Is a noise measurement sensible to zero point fluctuations ? With regard to these questions, we try to give theoretical and experimental answers by measuring the current fluctuations in a tunnel junction at microwave frequencies . Using these results, we investigate the question of the dynamical control of elementary excitations.

[1] Wave-packet approach to noise in multichannel mesoscopic systems. Th. Martin and R. Landauer. Phys. Rev. B 45, 1742 (1992)