Counting statistics and dephasing transition in an electronic Mach-Zehnder interferometer

In this paper the authors study the dependence of the visibility of the Aharonov-Bohm oscillations of an electronic Mach-Zehnder interferometer upon the transmission properties of an additional quantum point contact placed in front of the interferometer's input. According to a theory by I. P. Levkivskyi and E. V. Sukhorukov (Phys. Rev. Lett. 103, 036801 (2009)), a non-equilibrium noise-induced phase transition is meant to occur when the transmission of the point contact equals 1/2. The authors present experimental evidence for the existence of this critical point. It was recently suggested that a novel type of phase transition may occur in the visibility of electronic Mach-Zehnder interferometers. Here, we present experimental evidence for the existence of this transition. The transition is induced by strongly non-Gaussian noise that originates from the strong coupling of a quantum point contact to the interferometer. We provide a transparent physical picture of the effect by exploiting a close analogy to the neutrino oscillations of particle physics. In addition, our experiment constitutes a probe of the singularity of the elusive full counting statistics of a quantum point contact.