def test_construct_subcircuit(self):
"""Test correct subcircuits constructed"""
dev = qml.device("default.qubit", wires=2)
def circuit(a, b, c):
qml.RX(a, wires=0)
qml.RY(b, wires=0)
qml.CNOT(wires=[0, 1])
qml.PhaseShift(c, wires=1)
return qml.expval(qml.PauliX(0)), qml.expval(qml.PauliX(1))
circuit = QubitQNode(circuit, dev)
circuit.metric_tensor([1, 1, 1], only_construct=True)
res = circuit._metric_tensor_subcircuits
# first parameter subcircuit
assert len(res[(0, )]["queue"]) == 0
assert res[(0, )]["scale"] == [-0.5]
assert isinstance(res[(0, )]["observable"][0], qml.PauliX)
# second parameter subcircuit
assert len(res[(1, )]["queue"]) == 1
assert res[(1, )]["scale"] == [-0.5]
assert isinstance(res[(1, )]["queue"][0], qml.RX)
assert isinstance(res[(1, )]["observable"][0], qml.PauliY)
# third parameter subcircuit
assert len(res[(2, )]["queue"]) == 3
assert res[(2, )]["scale"] == [1]
assert isinstance(res[(2, )]["queue"][0], qml.RX)
assert isinstance(res[(2, )]["queue"][1], qml.RY)
assert isinstance(res[(2, )]["queue"][2], qml.CNOT)
assert isinstance(res[(2, )]["observable"][0], qml.Hermitian)
assert np.all(res[(
2, )]["observable"][0].params[0] == qml.PhaseShift.generator[0])
def test_evaluate_subcircuits(self, tol):
"""Test subcircuits evaluate correctly"""
dev = qml.device("default.qubit", wires=2)
def circuit(a, b, c):
qml.RX(a, wires=0)
qml.RY(b, wires=0)
qml.CNOT(wires=[0, 1])
qml.PhaseShift(c, wires=1)
return qml.expval(qml.PauliX(0)), qml.expval(qml.PauliX(1))
circuit = QubitQNode(circuit, dev)
a = 0.432
b = 0.12
c = -0.432
# evaluate subcircuits
circuit.metric_tensor((a, b, c))
# first parameter subcircuit
res = circuit._metric_tensor_subcircuits[(0, )]["result"]
expected = 0.25
assert np.allclose(res, expected, atol=tol, rtol=0)
# second parameter subcircuit
res = circuit._metric_tensor_subcircuits[(1, )]["result"]
expected = np.cos(a)**2 / 4
assert np.allclose(res, expected, atol=tol, rtol=0)
# third parameter subcircuit
res = circuit._metric_tensor_subcircuits[(2, )]["result"]
expected = (3 - 2 * np.cos(a)**2 * np.cos(2 * b) - np.cos(2 * a)) / 16
assert np.allclose(res, expected, atol=tol, rtol=0)
def test_no_generator(self):
"""Test exception is raised if subcircuit contains an
operation with no generator"""
dev = qml.device("default.qubit", wires=1)
def circuit(a):
qml.Rot(a, 0, 0, wires=0)
return qml.expval(qml.PauliX(0))
circuit = QubitQNode(circuit, dev)
with pytest.raises(QuantumFunctionError, match="has no defined generator"):
circuit.metric_tensor([1], only_construct=True)
def test_evaluate_diag_metric_tensor(self, tol):
"""Test that a diagonal metric tensor evaluates correctly"""
dev = qml.device("default.qubit", wires=2)
def circuit(a, b, c):
qml.RX(a, wires=0)
qml.RY(b, wires=0)
qml.CNOT(wires=[0, 1])
qml.PhaseShift(c, wires=1)
return qml.expval(qml.PauliX(0)), qml.expval(qml.PauliX(1))
circuit = QubitQNode(circuit, dev)
a = 0.432
b = 0.12
c = -0.432
# evaluate metric tensor
g = circuit.metric_tensor((a, b, c))
# check that the metric tensor is correct
expected = (np.array([
1,
np.cos(a)**2,
(3 - 2 * np.cos(a)**2 * np.cos(2 * b) - np.cos(2 * a)) / 4
]) / 4)
assert np.allclose(g, np.diag(expected), atol=tol, rtol=0)
def test_generator_no_expval(self, monkeypatch):
"""Test exception is raised if subcircuit contains an
operation with generator object that is not an observable"""
dev = qml.device("default.qubit", wires=1)
def circuit(a):
qml.RX(a, wires=0)
return qml.expval(qml.PauliX(0))
circuit = QubitQNode(circuit, dev)
with monkeypatch.context() as m:
m.setattr("pennylane.RX.generator", [qml.RX, 1])
with pytest.raises(QuantumFunctionError, match="no corresponding observable"):
circuit.metric_tensor([1], only_construct=True)
def test_construct_subcircuit_layers(self):
"""Test correct subcircuits constructed
when a layer structure exists"""
dev = qml.device("default.qubit", wires=3)
def circuit(params):
# section 1
qml.RX(params[0], wires=0)
# section 2
qml.RY(params[1], wires=0)
qml.CNOT(wires=[0, 1])
qml.CNOT(wires=[1, 2])
# section 3
qml.RX(params[2], wires=0)
qml.RY(params[3], wires=1)
qml.RZ(params[4], wires=2)
qml.CNOT(wires=[0, 1])
qml.CNOT(wires=[1, 2])
# section 4
qml.RX(params[5], wires=0)
qml.RY(params[6], wires=1)
qml.RZ(params[7], wires=2)
qml.CNOT(wires=[0, 1])
qml.CNOT(wires=[1, 2])
return qml.expval(qml.PauliX(0)), qml.expval(
qml.PauliX(1)), qml.expval(qml.PauliX(2))
circuit = QubitQNode(circuit, dev)
params = np.ones([8])
circuit.metric_tensor([params], only_construct=True)
res = circuit._metric_tensor_subcircuits
# this circuit should split into 4 independent
# sections or layers when constructing subcircuits
assert len(res) == 4
# first layer subcircuit
layer = res[(0, )]
assert len(layer["queue"]) == 0
assert len(layer["observable"]) == 1
assert isinstance(layer["observable"][0], qml.PauliX)
# second layer subcircuit
layer = res[(1, )]
assert len(layer["queue"]) == 1
assert len(layer["observable"]) == 1
assert isinstance(layer["queue"][0], qml.RX)
assert isinstance(layer["observable"][0], qml.PauliY)
# third layer subcircuit
layer = res[(2, 3, 4)]
assert len(layer["queue"]) == 4
assert len(layer["observable"]) == 3
assert isinstance(layer["queue"][0], qml.RX)
assert isinstance(layer["queue"][1], qml.RY)
assert isinstance(layer["queue"][2], qml.CNOT)
assert isinstance(layer["queue"][3], qml.CNOT)
assert isinstance(layer["observable"][0], qml.PauliX)
assert isinstance(layer["observable"][1], qml.PauliY)
assert isinstance(layer["observable"][2], qml.PauliZ)
# fourth layer subcircuit
layer = res[(5, 6, 7)]
assert len(layer["queue"]) == 9
assert len(layer["observable"]) == 3
assert isinstance(layer["queue"][0], qml.RX)
assert isinstance(layer["queue"][1], qml.RY)
assert isinstance(layer["queue"][2], qml.CNOT)
assert isinstance(layer["queue"][3], qml.CNOT)
assert isinstance(layer["queue"][4], qml.RX)
assert isinstance(layer["queue"][5], qml.RY)
assert isinstance(layer["queue"][6], qml.RZ)
assert isinstance(layer["queue"][7], qml.CNOT)
assert isinstance(layer["queue"][8], qml.CNOT)
assert isinstance(layer["observable"][0], qml.PauliX)
assert isinstance(layer["observable"][1], qml.PauliY)
assert isinstance(layer["observable"][2], qml.PauliZ)