Enhanced quantum estimation via purification
Holger Mack, Dietmar Fischer, Matthias Freyberger · Physical Review A · 2000
We analyze the estimation of a finite ensemble of quantum bits that have been sent through a depolarizing channel. Instead of using the depolarized qubits directly, we first apply a purification step and show that this improves the fidelity of subsequent quantum estimation. Even though we lose some qubits of our finite ensemble the information is concentrated in the remaining purified ones.