Quantum-to-Classical Transition via Single-Shot Generalized Measurements

We establish an operational connection between discrete rounds of generalized measurements and continuous-time decoherence, with an explicit correspondence between the number of measurement rounds and the evolution time. Operationally, we show that a single round of such a generalized measurement eliminates quasiprobability negativity in finite-dimensional systems. From the decoherence perspective, this loss of negativity occurs abruptly at a critical time. In particular, this critical time can be shorter than the conventional decoherence time, indicating that the latter does not always faithfully track the disappearance of nonclassicality. Our results provide new insight into the quantum-to-classical transition in finite-dimensional systems from the viewpoint of phase-space quasiprobability, and suggest feasible quantum-circuit tests as well as possible heralded resource extraction from noise.