# von Neumann entropy

## EnglishEdit

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### EtymologyEdit

Named after John von Neumann.

### PronunciationEdit

• IPA(key): /vɔn ˈnoɪ.mən ˈɛn.tɹə.pi/

### NounEdit

von Neumann entropy

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