A Quantum Theory with Non-Collapsing Measurements

Vincenzo Fiorentino; Stefan Weigert

doi:10.1016/j.physleta.2025.130903

A Quantum Theory with Non-Collapsing Measurements

Vincenzo Fiorentino^*, Stefan Weigert

^*Corresponding author for this work

Mathematics

Research output: Contribution to journal › Article › peer-review

Abstract

A collapse-free version of quantum theory is examined to systematically study
the role of the projection postulate.
This foil theory assumes “passive”
measurements that do not update quantum states although measurement
outcomes still occur probabilistically, and in accordance with Born’s rule.
The Hilbert space setting of quantum theory is retained. “Passive quan-
tum theory” is shown to reproduce preparational uncertainty relations, the
no-cloning theorem, and no-signalling, among other properties. Striking dif-
ferences occur, however, if protocols involve post-measurement states. For
example, a single system, rather than an ensemble, is sufficient to reconstruct
the state of the system. The possibility to “observe” a state increases the
computational power of some quantum algorithms. Passive quantum theory
is not locally tomographic but capable of “simulating” quantum measure-
ments modulo a finite delay. Outcome probabilities for composite systems
may violate Bell inequalities, without however entailing an argument against
local hidden variables.

Original language	English
Article number	130903
Journal	Physics Letters A
Volume	559
Early online date	22 Aug 2025
DOIs	https://doi.org/10.1016/j.physleta.2025.130903
Publication status	Published - 5 Nov 2025

Bibliographical note

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Cite this

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