The quantum antidot electrometer: Direct observation of fractional charge

A Quantum Antidot electrometer has been used in the first direct observatio n of the fractionally quantized electric charge. In this paper, after intro ductory remarks, we review recent experiments performed on the integer i = 1, 2 and fractional f = 1/3 quantum Hall plateaus extending over a filling factor range of at least 27%. On the integer plateaus we directly measure e lectron's charge, in Coulombs, with standard deviation of 0.7% and absolute accuracy of 0.035c. We further find the charge of the f = 1/3 Laughlin qua siparticles to be invariantly e/3, with standard deviation of 1.2%, indepen dent of filling factor nu, tunneling current, and temperature.