qiskit.quantum_info.purity

purity(state, validate=True)

Calculate the purity of a quantum state.

The purity of a density matrix $\rho$ is

Parameters

• state (Statevector orDensityMatrix) – a quantum state.
• validate (bool) – check if input state is valid [Default: True]

Returns

the purity $Tr[\rho^2]$.

Return type

float

Raises

QiskitError – if the input isn’t a valid quantum state.