Information-Disturbance Tradeoff in Estimating the Unknown Three-Qubit GHZ State

In a recent paper, Sacchi (Phys. Rev. Lett. 96(2006)220502) studied the information-disturbance tradeoff in estimating an unknown two-qubit maximally entangled state. In this study, we explore the
tradeoff in estimating an unknown three-qubit GHZ state. The optimal
estimation process supplies a fidelity of 13/54 and the tradeoff interpolates smoothly between non-informative measurement and optimal estimation process.