Suppression of interference in quantum Hall Mach-Zehnder geometry by upstream neutral modes

TL;DR

This paper investigates how upstream neutral modes in fractional quantum Hall states suppress interference in Mach-Zehnder interferometers, explaining the absence of observed anyonic interference and proposing disentanglement as a solution.

Contribution

It demonstrates that upstream neutral modes entangle with downstream modes, suppressing interference, and suggests charge-neutral mode disentanglement can restore interference signals.

Findings

Interference visibility is suppressed by upstream neutral modes.

Upstream neutral modes act as 'which path' detectors.

Disentangling charge-neutral modes can revive interference.

Abstract

Mach-Zehnder interferometry has been proposed as a probe for detecting the statistics of anyonic quasiparticles in fractional quantum Hall (FQH) states. Here we focus on interferometers made of multimode edge states with upstream modes. We find that the interference visibility is suppressed due to downstream-upstream mode entanglement; the latter serves as a "which path" detector to the downstream interfering trajectories. Our analysis tackles a concrete realization of filling factor 2/3, but its applicability goes beyond that specific case, and encompasses the recent observation of ubiquitous emergence of upstream neutral modes in FQH states. The latter, according to our analysis, goes hand in hand with the failure to observe Mach-Zehnder anyonic interference in fractional states. We point out how charge-neutral mode disentanglement will resuscitate the interference signal.