[A] team of quantum physicists led by Anton Zeilinger from the Faculty of Physics at the University of Vienna and from the IQOQI of the Austrian Academy of Sciences . . . used a "qutrit" -- a quantum system consisting of a single photon that can assume three distinguishable states. "We were able to demonstrate experimentally that quantum mechanical measurements cannot be interpreted in a classical way even when no entanglement is involved," Radek Lapkiewicz explains. The findings relate to the theoretical predictions by John Stewart Bell, Simon B. Kochen, and Ernst Specker.
Underlying source: Radek Lapkiewicz, Peizhe Li, Christoph Schaeff, Nathan K. Langford, Sven Ramelow, Marcin Wieśniak, Anton Zeilinger. Experimental non-classicality of an indivisible quantum system. Nature, 2011; 474 (7352): 490 DOI: 10.1038/nature10119
While the experiment merely confirms what was widely believed to be true already, the more ways that a conclusion is confirmed, the less room there is for an alternative theoretical explanation.