Realization of a Laughlin quasiparticle interferometer: Observation of fractional statistics

In two dimensions, the laws of physics permit the existence of anyons, particles with fractional statistics which are neither Fermi nor Bose. That is, upon exchange of two such particles, the quantum state of a system acquires a phase which is neither 0 nor $\pi$, but can be any value. The elementary excitations (Laughlin quasiparticles) of a fractional quantum Hall fluid have a fractional electric charge and are expected to obey fractional statistics. In this paper we report experimental realization of a Laughlin quasiparticle interferometer, where quasiparticles of the $1∕3$ fluid execute a closed path around an island of the $2∕5$ fluid and thus acquire statistical phase. Interference fringes are observed as conductance oscillations as a function of magnetic flux, similar to the Aharonov-Bohm effect. We observe the interference shift by one fringe upon introduction of five magnetic flux quanta $(5h∕e)$ into the island. The corresponding $2e$ charge period is confirmed directly in calibrated gate experiments. These results constitute direct observation of fractional statistics of Laughlin quasiparticles.