def test_apply(self, gate, apply_unitary, tol):
"""Test the application of gates to a state"""
dev = plf.NumpyWavefunctionDevice(wires=3)
try:
# get the equivalent pennylane operation class
op = getattr(qml.ops, gate)
except AttributeError:
# get the equivalent pennylane-forest operation class
op = getattr(plf, gate)
# the list of wires to apply the operation to
w = list(range(op.num_wires))
obs = qml.expval(qml.PauliZ(0))
if op.par_domain == "A":
# the parameter is an array
if gate == "QubitUnitary":
p = np.array(U)
w = [0]
state = apply_unitary(U, 3)
elif gate == "BasisState":
p = np.array([1, 1, 1])
state = np.array([0, 0, 0, 0, 0, 0, 0, 1])
w = list(range(dev.num_wires))
circuit_graph = qml.CircuitGraph([op(p, wires=w)] + [obs], {},
dev.wires)
else:
p = [0.432_423, 2, 0.324][:op.num_params]
fn = test_operation_map[gate]
if callable(fn):
# if the default.qubit is an operation accepting parameters,
# initialise it using the parameters generated above.
O = fn(*p)
else:
# otherwise, the operation is simply an array.
O = fn
# calculate the expected output
state = apply_unitary(O, 3)
# Creating the circuit graph using a parametrized operation
if p:
circuit_graph = qml.CircuitGraph([op(*p, wires=w)] + [obs], {},
dev.wires)
# Creating the circuit graph using an operation that take no parameters
else:
circuit_graph = qml.CircuitGraph([op(wires=w)] + [obs], {},
dev.wires)
dev.apply(circuit_graph.operations,
rotations=circuit_graph.diagonalizing_gates)
res = dev.expval(obs)
# verify the device is now in the expected state
self.assertAllAlmostEqual(dev._state, state, delta=tol)
def test_sample_values(self, tol):
"""Tests if the samples returned by sample have
the correct values
"""
dev = plf.NumpyWavefunctionDevice(wires=1, shots=10)
phi = 1.5708
circuit_operations = [qml.RX(phi, wires=[0])]
O = qml.sample(qml.PauliZ(0))
observables = [O]
circuit_graph = qml.CircuitGraph(circuit_operations + observables, {},
dev.wires)
# test correct variance for <Z> of a rotated state
dev.apply(circuit_graph.operations,
rotations=circuit_graph.diagonalizing_gates)
dev._samples = dev.generate_samples()
s1 = dev.sample(O)
# s1 should only contain 1 and -1
self.assertAllAlmostEqual(s1**2, 1, delta=tol)
def test_var_hermitian(self, tol):
"""Tests for variance calculation using an arbitrary Hermitian observable"""
dev = plf.NumpyWavefunctionDevice(wires=2)
phi = 0.543
theta = 0.6543
H = np.array([[4, -1 + 6j], [-1 - 6j, 2]])
circuit_operations = [qml.RX(phi, wires=[0]), qml.RY(theta, wires=[0])]
O = qml.var(qml.Hermitian(H, wires=[0]))
observables = [O]
circuit_graph = qml.CircuitGraph(circuit_operations + observables, {},
dev.wires)
# test correct variance for <Z> of a rotated state
dev.apply(circuit_graph.operations,
rotations=circuit_graph.diagonalizing_gates)
var = dev.var(O)
# test correct variance for <H> of a rotated state
expected = 0.5 * (2 * np.sin(2 * theta) * np.cos(phi)**2 +
24 * np.sin(phi) * np.cos(phi) *
(np.sin(theta) - np.cos(theta)) +
35 * np.cos(2 * phi) + 39)
self.assertAlmostEqual(var, expected, delta=tol)
def test_multi_mode_hermitian_expectation(self, theta, phi, varphi, tol):
"""Test that arbitrary multi-mode Hermitian expectation values are correct"""
A = np.array([
[-6, 2 + 1j, -3, -5 + 2j],
[2 - 1j, 0, 2 - 1j, -5 + 4j],
[-3, 2 + 1j, 0, -4 + 3j],
[-5 - 2j, -5 - 4j, -4 - 3j, -6],
])
dev = DefaultQubitTF(wires=2)
queue = [
qml.RY(theta, wires=0),
qml.RY(phi, wires=1),
qml.CNOT(wires=[0, 1])
]
observables = [qml.Hermitian(A, wires=[0, 1])]
for i in range(len(observables)):
observables[i].return_type = qml.operation.Expectation
res = dev.execute(
qml.CircuitGraph(queue + observables, {}, Wires([0, 1])))
# below is the analytic expectation value for this circuit with arbitrary
# Hermitian observable A
expected = 0.5 * (6 * np.cos(theta) * np.sin(phi) - np.sin(theta) *
(8 * np.sin(phi) + 7 * np.cos(phi) + 3) -
2 * np.sin(phi) - 6 * np.cos(phi) - 6)
assert np.allclose(res, expected, atol=tol, rtol=0)
def test_hermitian_expectation(self, theta, phi, varphi, tol):
"""Test that arbitrary Hermitian expectation values are correct"""
dev = DefaultQubitTF(wires=2)
queue = [
qml.RY(theta, wires=0),
qml.RY(phi, wires=1),
qml.CNOT(wires=[0, 1])
]
observables = [qml.Hermitian(A, wires=[i]) for i in range(2)]
for i in range(len(observables)):
observables[i].return_type = qml.operation.Expectation
res = dev.execute(
qml.CircuitGraph(queue + observables, {}, Wires([0, 1])))
a = A[0, 0]
re_b = A[0, 1].real
d = A[1, 1]
ev1 = ((a - d) * np.cos(theta) +
2 * re_b * np.sin(theta) * np.sin(phi) + a + d) / 2
ev2 = ((a - d) * np.cos(theta) * np.cos(phi) + 2 * re_b * np.sin(phi) +
a + d) / 2
expected = np.array([ev1, ev2])
assert np.allclose(res, expected, atol=tol, rtol=0)
def test_single_wire_expectation(self, gate, obs, expected, theta, phi, varphi, tol):
"""Test that identity expectation value (i.e. the trace) is 1"""
dev = DefaultQubitTF(wires=2)
queue = [gate(theta, wires=0), gate(phi, wires=1), qml.CNOT(wires=[0, 1])]
observables = [obs(wires=[i]) for i in range(2)]
for i in range(len(observables)):
observables[i].return_type = qml.operation.Expectation
res = dev.execute(qml.CircuitGraph(queue + observables, {}, Wires([0, 1, 2])))
assert np.allclose(res, expected(theta, phi), atol=tol, rtol=0)
def test_var(self, theta, phi, varphi, tol):
"""Tests for variance calculation"""
dev = DefaultQubitTF(wires=1)
# test correct variance for <Z> of a rotated state
queue = [qml.RX(phi, wires=0), qml.RY(theta, wires=0)]
observables = [qml.PauliZ(wires=[0])]
for i in range(len(observables)):
observables[i].return_type = qml.operation.Variance
res = dev.execute(qml.CircuitGraph(queue + observables, {}, Wires([0])))
expected = 0.25 * (3 - np.cos(2 * theta) - 2 * np.cos(theta) ** 2 * np.cos(2 * phi))
assert np.allclose(res, expected, atol=tol, rtol=0)
def test_sample_values_hermitian_multi_qubit(self, tol):
"""Tests if the samples of a multi-qubit Hermitian observable returned by sample have
the correct values
"""
shots = 1_000_000
dev = plf.NumpyWavefunctionDevice(wires=2, shots=shots)
theta = 0.543
A = np.array([
[1, 2j, 1 - 2j, 0.5j],
[-2j, 0, 3 + 4j, 1],
[1 + 2j, 3 - 4j, 0.75, 1.5 - 2j],
[-0.5j, 1, 1.5 + 2j, -1],
])
circuit_operations = [
qml.RX(theta, wires=[0]),
qml.RY(2 * theta, wires=[1]),
qml.CNOT(wires=[0, 1]),
]
O = qml.sample(qml.Hermitian(A, wires=[0, 1]))
observables = [O]
circuit_graph = qml.CircuitGraph(circuit_operations + observables, {},
dev.wires)
dev.apply(circuit_graph.operations,
rotations=circuit_graph.diagonalizing_gates)
dev._samples = dev.generate_samples()
s1 = dev.sample(O)
# s1 should only contain the eigenvalues of
# the hermitian matrix
eigvals = np.linalg.eigvalsh(A)
assert np.allclose(sorted(list(set(s1))),
sorted(eigvals),
atol=tol,
rtol=0)
# make sure the mean matches the analytic mean
expected = (88 * np.sin(theta) + 24 * np.sin(2 * theta) -
40 * np.sin(3 * theta) + 5 * np.cos(theta) -
6 * np.cos(2 * theta) + 27 * np.cos(3 * theta) + 6) / 32
assert np.allclose(np.mean(s1), expected, atol=0.1, rtol=0)
def graph(self):
"""Returns a directed acyclic graph representation of the recorded
quantum circuit:
>>> tape.graph
<pennylane.circuit_graph.CircuitGraph object at 0x7fcc0433a690>
Note that the circuit graph is only constructed once, on first call to this property,
and cached for future use.
Returns:
.CircuitGraph: the circuit graph object
"""
if self._graph is None:
self._graph = qml.CircuitGraph(self.operations, self.observables,
self.wires, self._par_info,
self.trainable_params)
return self._graph
def test_sample_values_hermitian(self, tol):
"""Tests if the samples of a Hermitian observable returned by sample have
the correct values
"""
dev = plf.NumpyWavefunctionDevice(wires=1, shots=1_000_000)
theta = 0.543
A = np.array([[1, 2j], [-2j, 0]])
circuit_operations = [qml.RX(theta, wires=[0])]
O = qml.sample(qml.Hermitian(A, wires=[0]))
observables = [O]
circuit_graph = qml.CircuitGraph(circuit_operations + observables, {},
dev.wires)
dev.apply(circuit_graph.operations,
rotations=circuit_graph.diagonalizing_gates)
dev._samples = dev.generate_samples()
s1 = dev.sample(O)
# s1 should only contain the eigenvalues of
# the hermitian matrix
eigvals = np.linalg.eigvalsh(A)
assert np.allclose(sorted(list(set(s1))),
sorted(eigvals),
atol=tol,
rtol=0)
# the analytic mean is 2*sin(theta)+0.5*cos(theta)+0.5
assert np.allclose(np.mean(s1),
2 * np.sin(theta) + 0.5 * np.cos(theta) + 0.5,
atol=0.1,
rtol=0)
# the analytic variance is 0.25*(sin(theta)-4*cos(theta))^2
assert np.allclose(np.var(s1),
0.25 * (np.sin(theta) - 4 * np.cos(theta))**2,
atol=0.1,
rtol=0)
def test_var_hermitian(self, theta, phi, varphi, tol):
"""Tests for variance calculation using an arbitrary Hermitian observable"""
dev = DefaultQubitTF(wires=2)
# test correct variance for <H> of a rotated state
H = np.array([[4, -1 + 6j], [-1 - 6j, 2]])
queue = [qml.RX(phi, wires=0), qml.RY(theta, wires=0)]
observables = [qml.Hermitian(H, wires=[0])]
for i in range(len(observables)):
observables[i].return_type = qml.operation.Variance
res = dev.execute(qml.CircuitGraph(queue + observables, {}))
expected = 0.5 * (2 * np.sin(2 * theta) * np.cos(phi)**2 +
24 * np.sin(phi) * np.cos(phi) *
(np.sin(theta) - np.cos(theta)) +
35 * np.cos(2 * phi) + 39)
assert np.allclose(res, expected, atol=tol, rtol=0)
def test_var(self, tol, qvm):
"""Tests for variance calculation"""
dev = plf.WavefunctionDevice(wires=2)
phi = 0.543
theta = 0.6543
circuit_operations = [qml.RX(phi, wires=[0]), qml.RY(theta, wires=[0])]
O = qml.var(qml.PauliZ(wires=[0]))
observables = [O]
circuit_graph = qml.CircuitGraph(circuit_operations + observables, {})
# test correct variance for <Z> of a rotated state
dev.apply(circuit_graph.operations,
rotations=circuit_graph.diagonalizing_gates)
var = dev.var(qml.PauliZ(0))
expected = 0.25 * (3 - np.cos(2 * theta) -
2 * np.cos(theta)**2 * np.cos(2 * phi))
self.assertAlmostEqual(var, expected, delta=tol)
def metric_tensor(self,
args,
kwargs=None,
*,
diag_approx=False,
only_construct=False):
"""Evaluate the value of the metric tensor.
Args:
args (tuple[Any]): positional (differentiable) arguments
kwargs (dict[str, Any]): auxiliary arguments
diag_approx (bool): iff True, use the diagonal approximation
only_construct (bool): Iff True, construct the circuits used for computing
the metric tensor but do not execute them, and return None.
Returns:
array[float]: metric tensor
"""
# pylint:disable=too-many-branches
kwargs = kwargs or {}
kwargs = self._default_args(kwargs)
if self.circuit is None or self.mutable:
# construct the circuit
self._construct(args, kwargs)
if self._metric_tensor_subcircuits is None:
self._construct_metric_tensor(diag_approx=diag_approx)
if only_construct:
return None
# temporarily store the parameter values in the Variable class
self._set_variables(args, kwargs)
tensor = np.zeros([self.num_variables, self.num_variables])
# execute constructed metric tensor subcircuits
for params, circuit in self._metric_tensor_subcircuits.items():
self.device.reset()
s = np.array(circuit["scale"])
V = circuit["eigenbasis_matrix"]
if not diag_approx:
# block diagonal approximation
unitary_op = qml.QubitUnitary(V,
wires=list(range(
self.num_wires)),
do_queue=False)
if isinstance(self.device, qml.QubitDevice):
ops = circuit["queue"] + [unitary_op
] + [qml.expval(qml.PauliZ(0))]
circuit_graph = qml.CircuitGraph(ops, self.variable_deps)
self.device.execute(circuit_graph)
else:
self.device.execute(
circuit["queue"] + [unitary_op],
[
qml.expval(qml.PauliZ(wire))
for wire in list(range(self.device.num_wires))
],
)
probs = list(self.device.probability())
first_order_ev = np.zeros([len(params)])
second_order_ev = np.zeros([len(params), len(params)])
for idx, ev in circuit["Ki_expectations"]:
first_order_ev[idx] = ev @ probs
for idx, ev in circuit["KiKj_expectations"]:
# idx is a 2-tuple (i, j), representing
# generators K_i, K_j
second_order_ev[idx] = ev @ probs
# since K_i and K_j are assumed to commute,
# <psi|K_j K_i|psi> = <psi|K_i K_j|psi>,
# and thus the matrix of second-order expectations
# is symmetric
second_order_ev[idx[1], idx[0]] = second_order_ev[idx]
g = np.zeros([len(params), len(params)])
for i, j in itertools.product(range(len(params)), repeat=2):
g[i, j] = (s[i] * s[j] *
(second_order_ev[i, j] -
first_order_ev[i] * first_order_ev[j]))
row = np.array(params).reshape(-1, 1)
col = np.array(params).reshape(1, -1)
circuit["result"] = np.diag(g)
tensor[row, col] = g
else:
# diagonal approximation
if isinstance(self.device, qml.QubitDevice):
circuit_graph = qml.CircuitGraph(
circuit["queue"] + circuit["observable"],
self.variable_deps)
variances = self.device.execute(circuit_graph)
else:
variances = self.device.execute(circuit["queue"],
circuit["observable"])
circuit["result"] = s**2 * variances
tensor[np.array(params), np.array(params)] = circuit["result"]
return tensor
