cirq.qis.fidelity

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Fidelity of two quantum states.

View aliases

Main aliases

`cirq.fidelity`, `cirq.qis.measures.fidelity`

cirq.qis.fidelity(
    state1: "cirq.QUANTUM_STATE_LIKE",
    state2: "cirq.QUANTUM_STATE_LIKE",
    qid_shape: Optional[Tuple[int, ...]] = None,
    validate: bool = True,
    atol: float = 1e-07
) -> float

The fidelity of two density matrices ρ and σ is defined as

trace(sqrt(sqrt(ρ) σ sqrt(ρ)))^2.

The given states can be state vectors or density matrices.

Args
state1	The first state.
state2	The second state.
qid_shape	The qid shape of the given states.
validate	Whether to check if the given states are valid quantum states.
atol	Absolute numerical tolerance to use for validation.

Returns
The fidelity.

Raises
ValueError	The qid shape of the given states was not specified and could not be inferred.
ValueError	Invalid quantum state.