Direct measurement of the destruction of charge quantization in a single-electron box

We report here direct measurements of the destruction of charge quantizatio n in a single-electron box, the first over the full range of box-to-lead co nductance values from G congruent to 0 to the conductance quantum G(Q) = 2e (2)/h, using a sensitive single-electron transistor (SET) electrometer. The sensitivity of the electrometer is measured to be delta q congruent to 6 x 10(-5) e/root Hz and its superiority to conductance measurements of charge fluctuations is clearly demonstrated. As the rate of quantum mechanical tu nneling from the box to its lead is increased, the quantization of charge i s destroyed, disappearing entirely at G = G(Q) in agreement with theory. (C ) 1999 American Institute of Physics. [S0003-6951(99)04303-X].