Speakable and unspeakable in quantum measurements

TL;DR

This paper compares orthodox quantum measurement limits with weak measurement approaches, concluding that orthodox limits are necessary and cannot be surpassed by weak measurements.

Contribution

It provides a direct comparison between orthodox quantum limits and weak measurement techniques, demonstrating the necessity of orthodox limits.

Findings

Orthodox quantum limits are confirmed as necessary.

Weak measurements do not surpass orthodox limits.

The study clarifies the relationship between different quantum measurement approaches.

Abstract

Quantum mechanics, in its orthodox version, imposes severe limits on what can be known, or even said, about the condition of a quantum system between two observations. A relatively new approach, based on so-called "weak measurements", suggests that such forbidden knowledge can be gained by studying the system's response to an inaccurate weakly perturbing measuring device. It goes further to propose revising the whole concept of physics variables, and offers various examples of counterintuitive quantum behaviour. Both views go to the very heart of quantum theory, and yet are rarely compared directly. A new technique must either transcend the orthodox limits, or just prove that these limits are indeed necessary. We study both possibilities, and find for the orthodoxy.