Interference measurements of non-Abelian e/4 & Abelian e/2 quasiparticle braiding

TL;DR

This study provides experimental evidence for non-Abelian e/4 quasiparticles in quantum Hall states at filling factors 5/2 and 7/2, demonstrating their stability and potential for topological quantum computing through interference measurements.

Contribution

First experimental observation of non-Abelian e/4 quasiparticles at ν=7/2 using interference in high purity heterostructures, including analysis of fermion parity stability.

Findings

Evidence of non-Abelian e/4 quasiparticles at ν=7/2

Stable fermion parity over hours near both filling factors

Observation of Abelian e/2 quasiparticle interference

Abstract

The quantum Hall states at filling factors $\nu=5/2$ and $7/2$ are expected to have Abelian charge $e/2$ quasiparticles and non-Abelian charge $e/4$ quasiparticles. The non-Abelian statistics of the latter has been predicted to display a striking interferometric signature, the even-odd effect. By measuring resistance oscillations as a function of magnetic field in Fabry-P\'erot interferometers using new high purity heterostructures, we for the first time report experimental evidence for the non-Abelian nature of excitations at $\nu=7/2$. At both $\nu=5/2$ and $7/2$ we also examine, for the first time, the fermion parity, a topological quantum number of an even number of non-Abelian quasiparticles. The phase of observed $e/4$ oscillations is reproducible and stable over long times (hours) near both filling factors, indicating stability of the fermion parity. At both fractions, when phase fluctuations are observed, they are predominantly $\pi$ phase flips, consistent with either fermion parity change or change in the number of the enclosed $e/4$ quasiparticles. We also examine lower-frequency oscillations attributable to Abelian interference processes in both states. Taken together, these results constitute new evidence for the non-Abelian nature of $e/4$ quasiparticles; the observed life-time of their combined fermion parity further strengthens the case for their utility for topological quantum computation.