We show that weighted unitary 2-designs define optimal measurements on the system-ancilla output state for ancilla-assisted process tomography of unital quantum channels. Examples include complete sets of mutually unbiased unitary-operator bases. Each of these specifies a minimal series of optimal orthogonal measurements. General quantum channels are also considered.
@article{arxiv.0711.1017,
title = {Optimizing quantum process tomography with unitary 2-designs},
author = {A. J. Scott},
journal= {arXiv preprint arXiv:0711.1017},
year = {2008}
}