Physics and Metaphysics of Wigner's Friends: Even Performed Premeasurements Have No Results

The unambiguous account of proper quantum phenomena must, in principle, include a description of all relevant features of experimental arrangement (Bohr). The measurement process is composed of premeasurement (quantum correlation of the system with the pointer variable) and an irreversible decoherence via interaction with an environment. The system ends up in a probabilistic mixture of the eigenstates of the measured observable. For the premeasurement stage, any attempt to introduce an outcome leads, as we show, to a logical contradiction, 1 = i. This nullifies claims that a modified concept of Wigner's friend, who just premeasures, can lead to valid results concerning quantum theory.

Automated summary

The proper account of quantum phenomena must include a description of all relevant features of experimental arrangement and the measurement process consists of premeasurement and an irreversible decoherence via interaction with an environment. The system ends up in a probabilistic mixture of eigenstates of the measured observable, and any attempt to introduce an outcome leads to a logical contradiction. Claims that a modified version of Wigner's friend concept can lead to valid results concerning quantum theory are nullified.