# cirq.von_neumann_entropy

Calculates the von Neumann entropy of a quantum state in bits.

The Von Neumann entropy is defined as $$- trace( \rho ln \rho)$$, for a density matrix $$\rho$$. This gives the amount of entropy in 'ebits' (bits of bipartite entanglement).

If state is a square matrix, it is assumed to be a density matrix rather than a (pure) state tensor.

state The quantum state.
qid_shape The qid shape of the given state.
validate Whether to check if the given state is a valid quantum state.
atol Absolute numerical tolerance to use for validation.

The calculated von Neumann entropy.

ValueError Invalid quantum state.

https://en.wikipedia.org/wiki/Von_Neumann_entropy

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{"lastModified": "Last updated 2024-06-27 UTC."}