Experimental observation of impossible-to-beat quantum advantage on a   hybrid photonic system
  Quantum resources outperform classical ones for certain communication and computational tasks. Remarkably, in some cases, the quantum advantage cannot be improved using hypothetical postquantum resources. A class of tasks with this property can be singled out using graph theory. Here we report the experimental observation of an impossible-to-beat quantum advantage on a four-dimensional quantum system defined by the polarization and orbital angular momentum of a single photon. The results show pristine evidence of the quantum advantage and are compatible with the maximum advantage allowed using postquantum resources. 
Eleonora Nagali, Vincenzo D'Ambrosio, Fabio Sciarrino, Adan Cabello
quant-ph