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_observable_with_no_eigvals(self):
"""An observable with no eigenvalues defined should cause
the eigvals property on the associated measurement process
to be None"""
obs = qml.NumberOperator(wires=0)
m = MeasurementProcess(Expectation, obs=obs)
assert m.eigvals is None
def test_error_obs_and_eigvals(self):
"""Test that providing both eigenvalues and an observable
results in an error"""
obs = qml.Hermitian(np.diag([1, 2, 3]), wires=[0, 1, 2])
with pytest.raises(ValueError, match="Cannot set the eigenvalues"):
MeasurementProcess(Expectation, obs=obs, eigvals=[0, 1])
def test_wires_match_observable(self):
"""Test that the wires of the measurement process
match an internal observable"""
obs = qml.Hermitian(np.diag([1, 2, 3]), wires=['a', 'b', 'c'])
m = MeasurementProcess(Expectation, obs=obs)
assert np.all(m.wires == obs.wires)
def test_eigvals_match_observable(self):
"""Test that the eigenvalues of the measurement process
match an internal observable"""
obs = qml.Hermitian(np.diag([1, 2, 3]), wires=[0, 1, 2])
m = MeasurementProcess(Expectation, obs=obs)
assert np.all(m.eigvals == np.array([1, 2, 3]))
# changing the observable data should be reflected
obs.data = [np.diag([5, 6, 7])]
assert np.all(m.eigvals == np.array([5, 6, 7]))
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]))