Non-Abelian properties at 5/2 and 7/2 filling factors exposed using controlled e/4 population of Fabry-Perot interferometers.

Essential to establishing non-Abelian statistics at 5/2 & 7/2 filling in interferometry experiments is determining the response to changing the interferometer’s enclosed e/4 quasiparticle (qp) number. Past interference measurements have shown results consistent with the even-odd effect, a sign of non-Abelian properties, in which resistance across the interferometer oscillates with changing the parity of the enclosed e/4 number: alternate braiding of an even versus odd number of e/4 qps should switch between an interference signal of the Abelian process where e/4 braid e/4 + e/4 versus the e/4 braiding e/4, marked by no interference due to fermion parity changes with each braid. Experimentally the e/4 qp number can be altered by i) changing the interferometer area by changing the device’s side gate voltage, ii) sweeping B-field, which systematically changes e/4 number by 10 qps for each flux quantum added to the interferometer area, iii) using a small central gate in the interferometer area that allows controlled single e/4 changes. The first two of these techniques have shown interference results consistent with non-Abelian properties at 5/2. The small central gate adjustment of e/4 number is a new experimental method: here we show our progress in this effort.