Measurement of the states of a coupled dot device

We analyse a method to measure the states of a coupled dot device (qubit). We derive a master equation to describe the unconditional evolution of the qubit when the measured records are averaged over and a conditional stochastic master equation describing the conditional evolution of the qubit. The approach is also extended to model a measurement scheme when there is a fluctuating energy gap between two electron states. From the calculated results the relevant device parameters can be estimated and optimum combination of the parameters can be selected.