Speaker
Description
Although the local precision limits of thermal equilibrium metrology are well established, the potential to enhance precision by driving a system into nonequilibrium remains largely unexplored. We first demonstrate that the precision limit of thermal equilibrium metrology can be surpassed by applying a unitary drive to the initial thermal equilibrium state. Our central result is to establish the supremum of the quantum Fisher information (QFI) under arbitrary unitary driving. We show that an optimized single quench is already sufficient to outperform thermal equilibrium metrology. Moreover, we identify an optimal protocol to achieve the supremum. Perhaps counter-intuitively, this QFI supremum is attainable by applying only two optimized quenches to the initial thermal equilibrium state. These findings provide both the fundamental precision limit and the optimal control strategies for local quantum metrology under unitary driving.