Quantum Hall valley splitters and tunable Mach-Zehnder interferometer in graphene

TL;DR

This paper demonstrates tunable electronic beam splitters and a Mach-Zehnder interferometer in graphene, advancing electron quantum optics by enabling coherent control of quantum Hall edge channels with valley polarization.

Contribution

It introduces fully tunable, coherent beam splitters in graphene for quantum Hall edge channels and constructs a tunable Mach-Zehnder interferometer, a significant step forward in electron quantum optics.

Findings

Beam splitters with transmission tunable from zero to near unity.

Realization of a fully tunable Mach-Zehnder interferometer in graphene.

Graphene shows greater robustness to quantum decoherence compared to conventional semiconductors.

Abstract

Graphene is a very promising test-bed for the field of electron quantum optics. However, a fully tunable and coherent electronic beam splitter is still missing. We report the demonstration of electronic beam splitters in graphene that couple quantum Hall edge channels having opposite valley polarizations. The electronic transmission of our beam splitters can be tuned from zero to near unity. By independently setting the beam splitters at the two corners of a graphene PN junction to intermediate transmissions, we realize a fully tunable electronic Mach-Zehnder interferometer. This tunability allows us to unambiguously identify the quantum interferences due to the Mach-Zehnder interferometer, and to study their dependence with the beam-splitter transmission and the interferometer bias voltage. The comparison with conventional semiconductor interferometers points towards universal processes driving the quantum decoherence in those two different 2D systems, with graphene being much more robust to their effect.