Robin, a good place to start would be pretty much any paper Chris Fuchs has ever written. See for example this one (p. 9-12). As Chris points out, the argument from the non-uniqueness of mixed state decompositions basically goes back to Einstein (in a version involving two-particle entanglement). From a modern perspective, where Einstein went wrong was in his further inference that QM therefore has to be incomplete.
Robin, a good place to start would be pretty much any paper Chris Fuchs has ever written. See for example this one (p. 9-12). As Chris points out, the argument from the non-uniqueness of mixed state decompositions basically goes back to Einstein (in a version involving two-particle entanglement). From a modern perspective, where Einstein went wrong was in his further inference that QM therefore has to be incomplete.