Interferometry measurements to examine Fermion parity at candidate non-Abelian filling factors

Fabry-Perot interferometer measurements have shown interference oscillations at 7/2 and 5/2 filling factors consistent with even-odd effect oscillations, an important indicator of non-Abelian excitations, in high quality high density heterostructures [1].  While these oscillations can be a direct consequence of the e/4 quasiparticle braiding an even/odd number of e/4 in the interferometer, thus expressing Fermion parity change in the interfering particle beam for each number parity change, specifically controlling and selectively expressing each Fermion parity is an experimental challenge. To this end, we have constructed a series of interferometer devices that are planned to allow specific single e/4 charge movement that would explicitly change the Fermion parity between the two possibilities. We review here the progress in this effort, extending from single cell interferometers to double cell interferometers with three controlled charging sites in the interferometer active areas. We describe the expected properties and our early results in these measurements.

[1]. R. L. Willett et al. Interference measurements of non-Abelian e/4 & Abelian e/2 quasiparticle braiding, Physical Review X 13 (2023).