Causality Constraints on Nonlocal Quantum Measurements
Sandu Popescu, Lev Vaidman
TL;DR
This paper explores how relativistic causality imposes constraints on measuring nonlocal quantum properties, revealing that some measurements necessary for quantum theory conflict with causality principles.
Contribution
It provides a detailed analysis of the measurability of nonlocal quantum operators and demonstrates causality-induced limitations on certain quantum measurements.
Findings
Verification measurements erase local information in entangled states
Measurability of some nonlocal operators contradicts causality
Certain projection operators cannot be measured without violating causality
Abstract
Consequences of relativistic causality for measurements of nonlocal characteristics of composite quantum systems are investigated. It is proved that verification measurements of entangled states necessarily erase local information. A complete analysis of measurability of nondegenerate spin operators of a system of two spin-1/2 particles is presented. It is shown that measurability of certain projection operators which play an important role in axiomatic quantum theory contradicts the causality principle.
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