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Shor's Conjecture Is True: Projective Measurements Suffice for Binary Accessible Information
Quantum Physics · Submitted 4 Aug 2026
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We prove the conjecture constructively in arbitrary finite dimension.
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The abstract, sentence by sentence
Shor conjectured that a von Neumann measurement attains the accessible information of every binary quantum ensemble. We prove the conjecture constructively in arbitrary finite dimension. For every finite-outcome positive operator-valued measure (POVM) $M$, we form an operator $T_M$ from the posterior label probabilities and show that its spectral projection-valued measure (PVM) $\Pi_M$ satisfies $I_{\Pi_M}(X{:}Y)\ge I_M(X{:}Y)$; every rank-one refinement retains the inequality. Two applications of Jensen's operator inequality prove the comparison and yield an exact concave variational formula for the accessible information. The result is a special case of the general theorem of Fang, Fawzi, and Fawzi on measured $f$-divergences; the proof below isolates the binary argument and makes the replacement $M\mapsto T_M\mapsto\Pi_M$ explicit.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Shor conjectured that a von Neumann measurement attains the accessible information of every binary quantum ensemble. | background 1.00 | 0.04 | 0.11 | speculative 0.72 |
| s1 | We prove the conjecture constructively in arbitrary finite dimension. | contribution 0.75 | 0.96 | 0.80 | asserted 1.00 |
| s2 | For every finite-outcome positive operator-valued measure (POVM) $M$, we form an operator $T_M$ from the posterior label probabilities and show that its spectral projection-valued measure (PVM) $\Pi_M$ satisfies $I_{\Pi_M}(X{:}Y)\ge I_M(X{:}Y)$; every rank-one refinement retains the inequality. | method 0.73 | 0.94 | 0.36 | asserted 1.00 |
| s3 | Two applications of Jensen's operator inequality prove the comparison and yield an exact concave variational formula for the accessible information. | method 0.94 | 0.90 | 0.08 | asserted 1.00 |
| s4 | The result is a special case of the general theorem of Fang, Fawzi, and Fawzi on measured $f$-divergences; the proof below isolates the binary argument and makes the replacement $M\mapsto T_M\mapsto\Pi_M$ explicit. | interpretation 0.64 | 0.68 | 0.06 | asserted 1.00 |
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Original abstract
Shor conjectured that a von Neumann measurement attains the accessible information of every binary quantum ensemble. We prove the conjecture constructively in arbitrary finite dimension. For every finite-outcome positive operator-valued measure (POVM) $M$, we form an operator $T_M$ from the posterior label probabilities and show that its spectral projection-valued measure (PVM) $\Pi_M$ satisfies $I_{\Pi_M}(X{:}Y)\ge I_M(X{:}Y)$; every rank-one refinement retains the inequality. Two applications of Jensen's operator inequality prove the comparison and yield an exact concave variational formula for the accessible information. The result is a special case of the general theorem of Fang, Fawzi, and Fawzi on measured $f$-divergences; the proof below isolates the binary argument and makes the replacement $M\mapsto T_M\mapsto\Pi_M$ explicit.
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States the same result 2 papers
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Binary ensembles have one generator; compactness covers singular states, giving a proof of Shor's finite-dimensional binary orthogonal-measurement conjecture.
Beyond Shor's Conjecture: Optimal Quantum Measurements at Fixed Error · 0.99
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Here, we conclusively settle this longstanding open problem.
Proof of Shor's conjecture on the accessible information of quantum dichotomies · 0.99
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