def _fidelity_result(
state_result: AnalysisResultData,
target: Union[Choi, DensityMatrix],
input_dim: int = 1,
):
"""Faster computation of fidelity from eigen decomposition"""
evals = state_result.extra["eigvals"]
evecs = state_result.extra["eigvecs"]
# Format target to statevector or densitymatrix array
name = "process_fidelity" if input_dim > 1 else "state_fidelity"
if target is None:
raise AnalysisError("No target state provided")
if isinstance(target, QuantumChannel):
target_state = Choi(target).data / input_dim
elif isinstance(target, BaseOperator):
target_state = np.ravel(Operator(target),
order="F") / np.sqrt(input_dim)
else:
# Statevector or density matrix
target_state = np.array(target)
if target_state.ndim == 1:
rho = evecs @ (evals / input_dim * evecs).T.conj()
fidelity = np.real(target_state.conj() @ rho @ target_state)
else:
sqrt_rho = evecs @ (np.sqrt(evals / input_dim) * evecs).T.conj()
eig = la.eigvalsh(sqrt_rho @ target_state @ sqrt_rho)
fidelity = np.sum(np.sqrt(np.maximum(eig, 0)))**2
return AnalysisResultData(name, fidelity)
def _fidelity_result(evals, evecs, target, qpt=False):
"""Faster computation of fidelity from eigen decomposition"""
# Format target to statevector or densitymatrix array
trace = np.sqrt(len(evals)) if qpt else 1
name = "process_fidelity" if qpt else "state_fidelity"
if target is None:
raise AnalysisError("No target state provided")
if isinstance(target, QuantumChannel):
target_state = Choi(target).data / trace
elif isinstance(target, BaseOperator):
target_state = np.ravel(Operator(target), order="F") / np.sqrt(trace)
else:
target_state = np.array(target)
if target_state.ndim == 1:
rho = evecs @ (evals / trace * evecs).T.conj()
fidelity = np.real(target_state.conj() @ rho @ target_state)
else:
sqrt_rho = evecs @ (np.sqrt(evals / trace) * evecs).T.conj()
eig = la.eigvalsh(sqrt_rho @ target_state @ sqrt_rho)
fidelity = np.sum(np.sqrt(np.maximum(eig, 0))) ** 2
return AnalysisResultData(name, fidelity)