Estimating Bell Diagonal States with Separable Measurements

Abstract: Quantum network protocols depend on the availability of shared entanglement. Given that entanglement generation and distribution are affected by noise, characterization of the shared entangled states is essential to bound the errors of the protocols. This work analyzes the estimation of Bell diagonal states within quantum networks, where operations are limited to local actions and classical communication. We demonstrate the advantages of Bayesian mean estimation over direct inversion and maximum likelihood estimation, providing analytical expressions for estimation risk and supporting our findings with numerical simulations.