Quantum mechanics is supposedly universal. That is,
applicable to any physical system on which experiments can be
made. However, the kind of phenomena that have made quantum
mechanics striking, like the nonexistence of definite
noncontextual values and the need of superpositions to describe
the state of a system is supposedly relevant only for
"subatomic" or "microscopic" systems. The prevalent idea is
that, the more complex the system is, the greater the effect of
noise and decoherence, thus quantum phenomena become
unobservable beyond relatively simple systems. Here we show
that there is an inequality for the correlations between three
sequential measurements, which must be satisfied by any
description with definite noncontextual values, but is violated
by quantum mechanics for any state of any physical system of
n>1 qubits. Its remarkable feature is that the violation
predicted by quantum mechanics is such that the maximum
tolerated error in the measurements allowing a violation of the
inequality grows with n. This opens the possibility of
observing quantum contextuality in complex systems.
