# von Neumann entropy

## English

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Wikipedia has an article on:

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### Etymology

Named after John von Neumann.

### Pronunciation

• IPA(key): /vɔn ˈnoɪ.mən ˈɛn.tɹə.pi/

### Noun

von Neumann entropy

1. (quantum mechanics) The entropy of a quantum state. If the state is expressed as a quantum density matrix $\rho$, then this entropy can be expressed mathematically as $S = -\text{tr}(\rho \log \rho)$ where $\text{tr}$ is the trace operator and the logarithm is natural.