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The canonical treatment of dissipation and decoherence in
quantum systems assumes that these effects may be described as
being due to a bath of harmonic oscillators. This kind of
environment, sometimes called the Caldeira-Leggett bath, leads
to Gaussian fluctuations of the bath variable coupling to
the quantum system. Examples include the electromagnetic field
fluctuations acting on an atom, or the phonon field coupled
to an electron. In addition, there are many cases where
this description remains at least approximately true, due to
the central limit theorem.
Nevertheless, as we go towards small nanostructures, we more frequently encounter situations where a strong coupling to intrinsically non-Gaussian fluctuations makes such an approach invalid. In this talk, I will begin by giving an overview regarding the basic physical features to be expected when dealing with non-Gaussian noise. Then I will illustrate the general discussion by looking at two models where the charge or current noise of discrete electrons is the source of non-Gaussian fluctuations. One of them deals with the equilibrium charge noise of a single electron level tunnel-coupled to a reservoir ("quantum telegraph noise"), while the other concerns the shot noise of a partitioned one-dimensional quantum wire or edge channel. When coupling these sources of noise to a charge qubit or an electronic Mach-Zehnder interferometer, the interference contrast (aka "visibility") may oscillate as a function of parameters such as time or voltage. This behaviour is in qualitative contrast to the expectations for any Gaussian environment, and I will mention an experiment where these features have been observed recently [I. Neder, F. Marquardt, M. Heiblum, D. Mahalu and V. Umansky, Nature Physics 3, 534 (2007); I. Neder and F. Marquardt, New J. Phys. 9, 112 (2007)]. |
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