Demystifying weak measurements

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Kastner, Ruth
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preprint description
A large literature has grown up around the proposed use of 'weak measurements' to allegedly provide information about hidden ontological features of quantum systems. This paper attempts to clarify the fact that 'weak measurements' are simply strong (projective) measurements on one member of an entangled pair, and that all such measurements thus effect complete disentanglement of the pair. The only thing 'weak' about them is that the correlation established via the entanglement does not correspond to eigenstates of the 'weakly measured observable' for the component system that is subject to the weak measurement. It is observed that complete disentanglement always occurs, whether post-­‐selection is performed before or after the pointer detection. Assertions in the literature that weak measurements leave a system negligibly disturbed are therefore inaccurate, and claims based on those assertions need to be critically reassessed.