But is it really the case that individual properties are lost? Or is this just an artificial feature of the mathematical formalism, with no counterpart in nature? Remarkably, experiments can be designed to settle the question.
Early in 2007, based on a proposal by Nobel Laureate Tony Leggett, Zeilinger’s group in Vienna performed the first experiment aimed at proving that the usual individual properties cannot indeed be ascribed to two entangled photons. A few months later, some researchers in CQT, together with colleagues from the University of Geneva, discovered a stronger criterion than the ones previously available, and could perform a new experiment that confirmed the previous conclusion while removing some unnecessary assumptions .
More recently, improvements have been presented as a follow-up of that work . In particular, it has been proved that the observation of quantum entanglement is incompatible with the presence, not only of the usual individual properties, but of any individual property whatsoever. In an entangled state, individual particles really lose their own properties and keep only strong inter-particle relations.