Gleason's theorem made simple: a Bloch-space perspective

Fuente: arXiv
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Main Author: de Bianchi, Massimiliano Sassoli
Format: Preprint
Published: 2026
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author de Bianchi, Massimiliano Sassoli
author_facet de Bianchi, Massimiliano Sassoli
contents Gleason's theorem is often cited as establishing the Born rule from the structure of Hilbert space, yet its original proof is mathematically sophisticated and rarely accessible to physicists. In this article we present a simple route to the essence of Gleason's result, using the generalized Bloch representation of quantum states. We show explicitly why non-Born probability rules exist for two-dimensional systems, and why they become impossible in dimension three and higher. Our argument does not reproduce Gleason's full mathematical theorem, but it clarifies why the Born rule is unavoidable in higher dimension and why qubits are truly exceptional.
format Preprint
id arxiv_https___arxiv_org_abs_2603_07745
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Gleason's theorem made simple: a Bloch-space perspective
de Bianchi, Massimiliano Sassoli
Quantum Physics
Gleason's theorem is often cited as establishing the Born rule from the structure of Hilbert space, yet its original proof is mathematically sophisticated and rarely accessible to physicists. In this article we present a simple route to the essence of Gleason's result, using the generalized Bloch representation of quantum states. We show explicitly why non-Born probability rules exist for two-dimensional systems, and why they become impossible in dimension three and higher. Our argument does not reproduce Gleason's full mathematical theorem, but it clarifies why the Born rule is unavoidable in higher dimension and why qubits are truly exceptional.
title Gleason's theorem made simple: a Bloch-space perspective
topic Quantum Physics
url https://arxiv.org/abs/2603.07745