  The single electron transistor (SET) is a prime candidate for reading out the
final state of a qubit in a solid state quantum computer. Such a measurement
requires the detection of sub-electron charge motion in the presence of random
charging events. We present a detection scheme where the signals from two SETs
are cross-correlated to suppress unwanted artifacts due to charge noise. This
technique is demonstrated by using the two SETs to detect the charge state of
two tunnel junction - coupled metal dots, thereby simulating charge transfer
and readout in a two qubit system. These measurements indicate that for
comparable buried dopant semiconductor architectures the minimum measurement
time required to distinguish between the two charge states is of the order of
10 ns.
