  We present a new and feasible test proving quantum contextuality in
four-dimensional Hiltbert space. In our scheme, a contradiction between quantum
mechanics and noncontextual hidden variables is revealed through the
measurement statistics of two joint measurements of an ensemble of
non-entangled qubits. The origin of nonclassicality is fully attributed to the
measurement process. Quantum optical realization using photon pairs and linear
optics are presented.

Quantum Physics