Optimal estimation of qubit mixed states with local measurements
Oriol Romero‐Isart, E. Bagán, MA Ballester Sánchez, RD Richard Gill, R. Muñoz-Tapia · TU/e Research Portal · 2005
We study the estimation problem of a general mixed qubit state with protocols based on local measurements. We obtain the asymptotic bound of the fidelity for these settings and show that they do not attain the optimal joint measurement bound. We present an explicit protocol that uses classical communication in a very efficient way and saturates the local bound. We also analyze the case of mixed states known to lie on an equatorial plane of the Bloch sphere.