In quantum statistical mechanics, **von Neumann entropy**, named after John von Neumann, is the extension of classical entropy concepts to the field of quantum mechanics. For a quantum-mechanical system described by a density matrix ρ, the von Neumann entropy is

where tr denotes the trace. If ρ is written in terms of its eigenvectors |1〉, |2〉, |3〉, ... as

then the von Neumann entropy is

In this form, *S* can be seen to be related to the Shannon entropy.

Read more about Von Neumann Entropy: Background, Definition, Properties, Uses

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