Underlining some limitations of the statistical formalism in quantum mechanics

Abstract

We show that two chosen ensembles of spin states, which are differently prepared but are described by the same density matrix in quantum mechanics, do not fully share the same measurable characteristics. One characteristic on which they differ is shown to be the variance of the spin along a given direction. We conclude that the statistical description of an ensemble of states as given by its density matrix, although sufficient in many cases, should be considered incomplete, as it does not fully describe the measurable characteristics of the ensemble. A discussion a posteriori on the problem is provided.

References in corpus (2)

• Quantum Phase Transitions and Bipartite Entanglement
• Quantum correlations in the two-photon decay of few-electron ions

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• Quantum mechanical evolution operator in the presence of a scalar linear potential: discussion on the evolved state
• Solving the Zeh problem about the density operator with higher-order statistics