Common tools for obtaining physical density matrices in experimental quantum state tomography are shown here to cause systematic errors. For example, using maximum likelihood or least squares optimization for state reconstruction, we observe a systematic underestimation of the fidelity and an overestimation of entanglement. A solution for this problem can be achieved by a linear evaluation of the data yielding reliable and computational simple bounds including error bars.
@article{arxiv.1310.8465,
title = {Systematic errors in current quantum state tomography tools},
author = {Christian Schwemmer and Lukas Knips and Daniel Richart and Tobias Moroder and Matthias Kleinmann and Otfried Gühne and Harald Weinfurter},
journal= {arXiv preprint arXiv:1310.8465},
year = {2015}
}