Experimental verification of a quantumness criterion for single systems   based on a Bell-like inequality
  In this letter, we propose and experimentally test a quantumness criterion for single systems. The criterion is based on the violation of an already reported classical inequality. This inequality is expressed in terms of joint probabilities that we identify as realizations of preparation-and-measurement schemes. Our analysis points out that superposition is the key notion to grasp the quantum nature of physical systems. We verify our criterion in an all-optical experimental setup with heralded single photons generated via spontaneous parametric down conversion and use exclusively projective preparations and projective measurements. 
Jhonny Castrill\'on, Omar Calder\'on, David A. Guzm\'an, Alejandra   Valencia, Boris A. Rodr\'guez
quant-ph