On the negative-result experiments in quantum mechanics

TL;DR

This paper discusses negative-result experiments in quantum mechanics, clarifying their interpretation as biased measurements and emphasizing the necessity of standard measurements for verification, thus providing a nuanced understanding of null measurements.

Contribution

It offers a new perspective on null measurements, framing them as biased measurements and clarifying their relation to standard quantum measurement processes.

Findings

Null measurements are equivalent to biased measurements with selective detection.

Wave-function collapse can be understood as a standard measurement process.

Verification of null measurement predictions requires irreversible system-detector interactions.

Abstract

We comment on the so-called negative-result experiments (also known as null measurements, interaction-free measurements, and so on) in quantum mechanics (QM), in the light of the new general understanding of the quantum-measurement processes, proposed recently. All experiments of this kind (null-measurements) can be understood as improper measurements with an intentionally biased detector set up, which introduces exclusion or selection of certain events. The prediction on the state of a microscopic system under study based on a null measurement, is sometimes dramatically described as ``wave-function collapse without any microsystem-detector interactions". Though certainly correct, such a prediction is just a consequence of the standard QM laws, not different from the situation in the so-called state-preparation procedure. Another closely related concept is the (first-class or) repeatable measurements. The verification of the prediction made by a null-measurement requires eventually a standard unbiased measurement involving the microsystem-macroscopic detector interactions, which are nonadiabatic, irreversible processes of signal amplification.