We introduce a simple protocol for adaptive quantum state tomography, which reduces the worst-case infidelity between the estimate and the true state from O(N−1/2) to O(N−1). It uses a single adaptation step and just one extra measurement setting. In a linear optical qubit experiment, we demonstrate a full order of magnitude reduction in infidelity (from 0.1 to 0.01) for a modest number of samples (N=3×104).
@article{arxiv.1303.0436,
title = {Adaptive quantum state tomography improves accuracy quadratically},
author = {D. H. Mahler and Lee A. Rozema and Ardavan Darabi and Chris Ferrie and Robin Blume-Kohout and A. M. Steinberg},
journal= {arXiv preprint arXiv:1303.0436},
year = {2013}
}