qiskit.quantum_info.state_fidelity

state_fidelity(state1, state2, validate=True)

Return the state fidelity between two quantum states.

The state fidelity $F$ for density matrix input states $\rho_1, \rho_2$ is given by

If one of the states is a pure state this simplifies to $F(\rho_1, \rho_2) = \langle\psi_1|\rho_2|\psi_1\rangle$, where $\rho_1 = |\psi_1\rangle\!\langle\psi_1|$.

Parameters

• state1 (Statevector orDensityMatrix) – the first quantum state.
• state2 (Statevector orDensityMatrix) – the second quantum state.
• validate (bool) – check if the inputs are valid quantum states [Default: True]

Returns

The state fidelity $F(\rho_1, \rho_2)$.

Return type

float

Raises

QiskitError – if validate=True and the inputs are invalid quantum states.