Fragile states are better for quantum metrology

Understand

In quantum metrology, quantum probe states are capable of estimating unknown physical parameters to precisions beyond classical limits.

• What qualities do such states possess? Here we relate the performance of a probe state at estimating a parameter $\phi$ -- as quantified by the quantum Fisher information -- to the amount of purity it loses when $\phi$ undergoes statistical fluctuation.
• This indicates that the better a state is for estimating $\phi$, the more it decoheres when $\phi$ is subject to noise.