We consider electron spin qubits in quantum dots and define a measurement efficiency e to characterize reliable measurements via n-shot read outs. We propose various implementations based on a double dot and quantum point contact (QPC) and show that the associated efficiencies e vary between 50% and 100%, allowing single-shot read out in the latter case. We model the read out microscopically and derive its time dynamics in terms of a generalized master equation, calculate the QPC current and show that it allows spin read out under realistic conditions.
@article{arxiv.cond-mat/0309023,
title = {Measurement efficiency and n-shot read out of spin qubits},
author = {Hans-Andreas Engel and Vitaly Golovach and Daniel Loss and L. M. K. Vandersypen and J. M. Elzerman and R. Hanson and L. P. Kouwenhoven},
journal= {arXiv preprint arXiv:cond-mat/0309023},
year = {2007}
}