Richard L. Greene Dissertation Award: Interferometry of Electrons and Anyons in Graphene

Two-dimensional (2D) electrons in large magnetic fields and low temperatures form quantum Hall states, where injected current flows ballistically in chiral edge states. At low temperatures, edge current coherence is maintained over long enough lengths (microns) that interferometers can reveal the current-carrying quasiparticle’s quantum phase. In fractional quantum Hall states, quasiparticles are expected to be anyons, with fractional charge and non-trivial braiding phase upon identical particle exchange, unlike conventional fermions or bosons. In this talk, I will present experiments constructing edge state interferometers in graphene to directly probe the fractional charge and anyon braiding phase in fractional quantum Hall states. We first demonstrate interference of electrons in integer quantum Hall states, revealing Aharonov-Bohm resistance oscillations [1]. Next, we uncover correlations between electrons in copropagating integer edge states that lead to unexpected phase jumps and oscillation frequency doubling [2]. Finally, we present interference of fractional charges and observation of the anyon braiding phase in two fractional quantum Hall states [3]. These results demonstrate how quantum coherent electronic devices reveal electronic correlations that are otherwise inaccessible via transport measurements and open the door for developing fault-tolerant qubits leveraging braided anyons in 2D materials.

This talk presents work done during my Ph.D. in Philip Kim’s lab at Harvard University.

[1] Y. Ronen, T. Werkmeister et al. Aharonov–Bohm effect in graphene-based Fabry–Pérot quantum Hall interferometers. Nature Nanotechnology 16, 563–569 (2021).

[2] T. Werkmeister et al. Strongly coupled edge states in a graphene quantum Hall interferometer. Nature Communications 15,6533 (2024).

[3] T. Werkmeister, J.R. Ehrets et al. Anyon braiding and telegraph noise in a graphene interferometer. Science 388, 730–735 (2025).