def test_expand_no_observable(self):
"""Check that an exception is raised if the measurement to
be expanded has no observable"""
m = MeasurementProcess(Probability, wires=qml.wires.Wires([0, 1]))
with pytest.raises(NotImplementedError, match="Cannot expand"):
m.expand()
def test_expand_hermitian(self, tol):
"""Test the expansion of an hermitian observable"""
H = np.array([[1, 2], [2, 4]])
obs = qml.Hermitian(H, wires=['a'])
m = MeasurementProcess(Expectation, obs=obs)
tape = m.expand()
assert len(tape.operations) == 1
assert tape.operations[0].name == "QubitUnitary"
assert tape.operations[0].wires.tolist() == ['a']
assert np.allclose(tape.operations[0].parameters[0], np.array([[-2, 1], [1, 2]]) / np.sqrt(5), atol=tol, rtol=0)
assert len(tape.measurements) == 1
assert tape.measurements[0].return_type is Expectation
assert tape.measurements[0].wires.tolist() == ['a']
assert np.all(tape.measurements[0].eigvals == np.array([0, 5]))
def test_expand_pauli(self):
"""Test the expansion of a Pauli observable"""
obs = qml.PauliX(0) @ qml.PauliY(1)
m = MeasurementProcess(Expectation, obs=obs)
tape = m.expand()
assert len(tape.operations) == 4
assert tape.operations[0].name == "Hadamard"
assert tape.operations[0].wires.tolist() == [0]
assert tape.operations[1].name == "PauliZ"
assert tape.operations[1].wires.tolist() == [1]
assert tape.operations[2].name == "S"
assert tape.operations[2].wires.tolist() == [1]
assert tape.operations[3].name == "Hadamard"
assert tape.operations[3].wires.tolist() == [1]
assert len(tape.measurements) == 1
assert tape.measurements[0].return_type is Expectation
assert tape.measurements[0].wires.tolist() == [0, 1]
assert np.all(tape.measurements[0].eigvals == np.array([1, -1, -1, 1]))