Correlated charge detection for read-out of a solid state quantum   computer
  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. 
T.M. Buehler, D.J. Reilly, R. Brenner, A.R. Hamilton, A.S. Dzurak,   R.G. Clark