Robust quantum coherence above the Fermi sea

TL;DR

This study experimentally investigates quantum coherence of high-energy quasiparticles in the integer quantum Hall regime, revealing unexpected robustness of interference visibility above a certain energy threshold, challenging existing theories.

Contribution

It provides the first experimental evidence of sustained quantum coherence at energies above the Fermi sea, contradicting current theoretical models.

Findings

Quantum interference visibility remains high above a certain energy threshold.

Visibility is almost independent of energy up to 130 μeV.

Results challenge existing theories on quasiparticle excitations in quantum Hall systems.

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~$\mu$eV, well above the thermal energy of the measured sample. This result is in strong contradiction with our theoretical predictions, which instead predict a continuous decrease of the interference visibility with increasing energy. This experiment raises serious questions concerning the understanding of excitations in the integer quantum Hall regime.