A NONINVASIVE VOLTAGE PROBE TO MEASURE COULOMB CHARGING

We have fabricated a quantum box device in close proximity to a one-di mensional (1D) ballistic channel, but in a separate circuit. This is a chieved using electron beam lithography to define sub-micron gates on a modulation doped GaAs/GaAlAs heterostructure containing a high mobil ity electron gas. When the 1D channel is biased in the tunneling regim e it is extremely sensitive to neighbouring electric fields, and there fore the potential variation in the quantum box. The resistance variat ion with voltage in this channel is calibrated by applying a known vol tage to the quantum box and in this way the Coulomb charging energy is measured in a non-invasive manner. The Coulomb charging caused by rem oval of electrons from the dot is detectable while immeasurably small currents flow through the dot. The measured charging energy is 500 mue V which compares well with that calculated from a measurement of the t otal capacitance between all the surrounding conducting regions and th e quantum box.