Robust quantum coherence above the Fermi sea

Abstract : In this paper we present an experiment where we measured the quantum coherence of a quasiparticle injected at a well-defined energy above the Fermi sea into the edge states of the integer quantum Hall regime. Electrons are introduced in an electronic Mach-Zehnder interferometer after passing through a quantum dot that plays the role of an energy filter. Measurements show that above a threshold injection energy, the visibility of the quantum interferences is almost independent of the energy. This is true even for high energies, up to 130 μeV, well above the thermal energy of the measured sample. This result is in contradiction with our theoretical predictions, which instead predict a continuous decrease of the interference visibility with increasing energy.