  In two dimensions, the laws of physics permit existence of anyons, particles
with fractional statistics which is 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 fractional
electric charge and are expected to obey fractional statistics. Here we report
experimental realization of a novel 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.
