Abstract
In quantum mechanics, general measurements often cause disturbance which may be exploited to quantify entanglement, nonlocality or quantumness. Imagine a bipartite state ρab shared by two parties a and b, and a von Neumann measurement performed locally on party a which does not disturb the local state ρa:=tr b ρab, but nevertheless may disturb the global state ρab. This disturbance is an indication of some kind of correlations or global effect in ρab which cannot be accounted for locally. We propose to use the maximum disturbance on ρab caused by locally non-disturbing measurements as a figure of merit quantifying the global effect (nonlocality), and investigate its fundamental properties. For general two-qubit states and some higher-dimensional symmetric states, we present analytic formulas for their global effects.