Experimental Test of the Kochen-Specker Theorem for Single Qubits using   Positive Operator-Valued Measures
  We present an experimental scheme for the implementation of arbitrary generalized measurements, represented by positive-operator valued measures, on the polarization of single photons, using linear optical devices. Further, we experimentally test a Kochen-Specker theorem for single qubits using positive operator-valued measures. Our experimental results for the first time disprove non-contextual hidden-variable theories, even for single qubits. 
Qiang Zhang, Hui Li, Tao Yang, Juan Yin, Jiangfeng Du, Jian-Wei Pan