Fractional quantum hall effect in a quantum point contact at filling fraction 5/2

Recent theories suggest that the quasiparticles that populate certain quantum Hall states should exhibit exotic braiding statistics that could be used to build topological quantum gates. Confined systems that support such states at a filling fraction ν = 5/2 are of particular interest for testing these predictions. Here, we report transport measurements of just such a system, which consists of a quantum point contact (QPC) in a two-dimensional GaAs/AlGaAs electron gas that itself exhibits a well-developed fractional quantum Hall effect at a bulk filling fraction νbulk = 5/2. We observe plateau-like features at an effective filling fraction of νQPC = 5/2 for lithographic contact widths of 1.2µm and 0.8µm, but not 0.5µm. Transport near νQPC = 5/2 in the QPCs is consistent with a picture of chiral Luttinger-liquid edge states with inter-edge tunnelling, suggesting that an incompressible state at νQPC = 5/2 forms in this confined geometry. The discovery1 of a fractional quantum Hall effect (FQHE) at the even-denominator filling fraction ν = 5/2 has sparked a series of experimental2–6 and theoretical7–9 studies, leading to a prevailing interpretation of the 5/2 state as comprising paired fermions condensed into a Bardeen–Cooper–Schrieffer-like state10–13. Within this picture, excitations of the 5/2 ground state possess non-abelian statistics14–16 and associated topological properties. The possibilit