Invariance of charge of Laughlin quasiparticles

A quantum antidot electrometer is used to measure the charge of bulk Laughlin quasiparticles on the f = 1/3 fractional quantum Hall plateau. We also report experiments performed on the integer i = 1 and 2 plateaus extending over a range of filling factors used to calibrate the electrometer, and to demonstrate independence of the charge measurement of filling factor. We find the charge of the Laughlin quasiparticles to be invariantly e/3, with a standard deviation of 1.2% and an absolute accuracy of 4%, independent of filling, tunneling current, and temperature.