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A simple proof of the strong subadditivity inequality

Michael A. Nielsen·Denes Petz
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Abstract

Arguably the deepest fact known about the von Neumann entropy, the strong subadditivity inequality is a potent hammer in the quantum information theorist's toolkit. This short tutorial describes a simple proof of strong subadditivity due to Petz [Rep. on Math. Phys. 23 (1), 57--65 (1986)]. It assumes only knowledge of elementary linear algebra and quantum mechanics.

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Michael A. Nielsen, Denes Petz. 2005-06-08. A simple proof of the strong subadditivity inequality. https://arxiv.org/abs/quant-ph/0408130

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