Dynamics of statistical distance: Quantum limits for two-level clocks
Samuel L. Braunstein, Gerard J Milburn · Physical Review A · 1995
We study the evolution of statistical distance on the Bloch sphere under unitary and nonunitary dynamics. This corresponds to studying the limits to clock precision for a clock constructed from a two-state system. We find that the initial motion away from pure states under nonunitary dynamics yields the greatest accuracy for a ``one-tick'' clock; in this case the clock's precision is not limited by the largest frequency of the system.