Systematic errors in current quantum state tomography tools

Understand

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.