Quantum Measurements and State Reduction

Izuru Fujiwara

Macdonald, Alan

Many writings about quantum measurement posit a universal state reduction: every quantum measurement is accompanied by a state reduction. The supplementary material (next page) provides many examples. However, there are measurements without a state reduction. So authors and teachers should refrain from stating that state reduction is universal.

Dan Cristian Marinescu, Gabriela M. Marinescu

Macdonald, Alan

Many writings about quantum measurement posit a universal state reduction: every quantum measurement is accompanied by a state reduction. The supplementary material (next page) provides many examples. However, there are measurements without a state reduction. So authors and teachers should refrain from stating that state reduction is universal.

Masanao Ozawa

An operational approach to quantum state reduction, the state change of the measured system caused by a measurement of an observable conditional upon the outcome of measurement, is founded without assuming the projection postulate in any stages of the measuring process. Whereas the conventional formula assumes that the probe measurement satisfies the projection postulate, a new formula for determining the state reduction shows that the state reduction does not depend on how the probe observable is measured, or in particular does not depend on whether the probe measurement satisfies the projection postulate or not, contrary to the longstanding attempts in showing how the macroscopic nature of probe detection provokes state reduction. 1.