Melting of interference in the fractional quantum Hall effect: Appearance of neutral modes

TL;DR

This study demonstrates that the emergence of upstream neutral modes in the fractional quantum Hall effect correlates with the suppression of anyonic interference, highlighting the impact of edge reconstruction and neutral modes on quantum coherence.

Contribution

It provides direct experimental evidence linking neutral modes to the disappearance of interference in FQHE, revealing new insights into edge reconstruction and quasiparticle behavior.

Findings

Neutral modes appear as bulk filling factor approaches 1.

Interference diminishes with increasing neutral mode activity.

Edge reconstruction leads to conductance plateaus and neutral modes.

Abstract

Electrons living in a two-dimensional world under a strong magnetic field - the so-called fractional quantum Hall effect (FQHE) - often manifest themselves as fractionally charged quasiparticles (anyons). Moreover, being under special conditions they are expected to be immune to the environment, thus may serve as building blocks for future quantum computers. Interference of such anyons is the very first step towards understanding their anyonic statistics. However, the complex edge-modes structure of the fractional quantum Hall states, combined with upstream neutral modes, have been suspected to prevent an observation of the much sought after interference of anyons. Here, we report of finding a direct correlation between the appearance of neutral modes and the gradual disappearance of interference in a Mach-Zehnder interferometer (MZI), as the bulk filling factor is lowered towards Landau filling {\nu}_B =1; followed by a complete interference quench at {\nu}_B=1. Specifically, the interference was found to start diminishing at {\nu}_B~1.5 with a growing upstream neutral mode, which was detected by a born upstream shot noise in the input quantum point contact (QPC) to the MZI. Moreover, at the same time a {\nu}_QPC =1/3 conductance plateau, carrying shot-noise, appeared in the transmission of the QPC - persisting until bulk filling {\nu}_B =1/2. We identified this conductance plateau to result from edge reconstruction, which leads to an upstream neutral mode. Here, we also show that even the particle-like quasiparticles are accompanied by upstream neutral modes, therefore suppressing interference in the FQHE regime.