  The ability to identify cause-effect relations is an essential component of
the scientific method. The identification of causal relations is generally
accomplished through statistical trials where alternative hypotheses are tested
against each other. Traditionally, such trials have been based on classical
statistics. However, classical statistics becomes inadequate at the quantum
scale, where a richer spectrum of causal relations is accessible. Here we show
that quantum strategies can greatly speed up the identification of causal
relations. We analyse the task of identifying the effect of a given variable,
and we show that the optimal quantum strategy beats all classical strategies by
running multiple equivalent tests in a quantum superposition. The same working
principle leads to advantages in the detection of a causal link between two
variables, and in the identification of the cause of a given variable.
