Theoretical Limits of Protocols for Distinguishing Different Unravelings

Abstract: The evolution of an open quantum system is often described by a master equation, which governs the dynamics of the statistical operator. The dynamics of a master equation can be expressed as an ensemble average over stochastic trajectories, known as stochastic unravelings, which correspond to different measurement schemes and provide a wavefunction-level description of the system's evolution. The fact that a given master equation admits multiple unravelings raises the question of whether these different stochastic descriptions can be operationally distinguished, as recently suggested. We analyze this possibility: we show that while unraveling-dependent quantities indeed differ at the mathematical level, as already known in the literature, they can only be computed once the measurement procedure implementing the unraveling is already given, rendering them inaccessible when the procedure is unknown.