>>> sigma_x = np.array([[0, 1], [1, 0]])
>>> hamiltonian = graph.constant_stf_operator(np.pi * sigma_x / 2)
>>> target = graph.target(sigma_x)
>>> infidelity = graph.infidelity_stf(
... sample_times=np.linspace(0, 0.5, 100),
... hamiltonian=hamiltonian,
... target=target,
... name="infidelity",
... )
>>> result = qctrl.functions.calculate_graph(graph=graph, output_node_names=["infidelity"])
>>> result.output["infidelity"]["value"]
0.5000000000260991