def test_all_wires_method(self):
"""Tests the ``all_wires()`` method."""
wires1 = Wires([1, 2, 3])
wires2 = Wires([1, 4, 5, 2])
wires3 = Wires([6, 5])
new_wires = Wires.all_wires([wires1, wires2, wires3])
assert new_wires.wire_tuple == (1, 2, 3, 4, 5, 6)
with pytest.raises(WireError, match="Expected a Wires object"):
Wires.all_wires([[3, 4], [8, 5]])
def obtain_binary_repr(self, n_qubits=None, wire_map=None):
"""Converts the list of Pauli words to a binary matrix.
Keyword args:
n_qubits (int): number of qubits to specify dimension of binary vector representation
wire_map (dict): dictionary containing all wire labels used in the Pauli word as keys,
and unique integer labels as their values
Returns:
array[bool]: a column matrix of the Pauli words in binary vector representation
"""
if wire_map is None:
self._wire_map = {
wire: c
for c, wire in enumerate(
Wires.all_wires([obs.wires
for obs in self.observables]).tolist())
}
else:
self._wire_map = wire_map
self._n_qubits = n_qubits
return convert_observables_to_binary_matrix(self.observables, n_qubits,
self._wire_map)
def convert_observables_to_binary_matrix(observables,
n_qubits=None,
wire_map=None):
"""Converts a list of Pauli words to the binary vector representation and yields a row matrix
of the binary vectors.
The dimension of the binary vectors will be implied from the highest wire being acted on
non-trivially by the Pauli words in observables.
**Usage example:**
>>> convert_observables_to_binary_matrix([PauliX(0) @ PauliY(2), PauliZ(0) @ PauliZ(1) @ PauliZ(2)])
array([[1., 1., 0., 0., 1., 0.],
[0., 0., 0., 1., 1., 1.]])
Args:
observables (list[Union[Identity, PauliX, PauliY, PauliZ, Tensor]]): the list of Pauli
words
Keyword args:
n_qubits (int): number of qubits to specify dimension of binary vector representation
wire_map (dict): dictionary containing all wire labels used in the Pauli words as keys, and
unique integer labels as their values
Returns:
array[array[bool]]: a matrix whose rows are Pauli words in binary vector representation
"""
m_cols = len(observables)
if wire_map is None:
all_wires = Wires.all_wires(
[pauli_word.wires for pauli_word in observables])
wire_map = {i: c for c, i in enumerate(all_wires)}
n_qubits_min = max(wire_map.values()) + 1
if n_qubits is None:
n_qubits = n_qubits_min
elif n_qubits < n_qubits_min:
raise ValueError(
"n_qubits must support the highest mapped wire index {},"
" instead got n_qubits={}.".format(n_qubits_min, n_qubits))
binary_mat = np.zeros((m_cols, 2 * n_qubits))
for i in range(m_cols):
binary_mat[i, :] = pauli_to_binary(observables[i],
n_qubits=n_qubits,
wire_map=wire_map)
return binary_mat
def active_wires(operators):
"""Returns the wires acted on by a set of operators.
Args:
operators (list[~.Operation]): operators for which
we are gathering the active wires
Returns:
Wires: wires activated by the specified operators
"""
list_of_wires = [op.wires for op in operators]
return Wires.all_wires(list_of_wires)
def _wire_map_from_pauli_pair(pauli_word_1, pauli_word_2):
"""Generate a wire map from the union of wires of two Paulis.
Args:
pauli_word_1 (.Operation): A Pauli word.
pauli_word_2 (.Operation): A second Pauli word.
Returns:
dict[Union[str, int], int]): dictionary containing all wire labels used
in the Pauli word as keys, and unique integer labels as their values.
"""
wire_labels = Wires.all_wires([pauli_word_1.wires,
pauli_word_2.wires]).labels
wire_map = {label: i for i, label in enumerate(wire_labels)}
return wire_map
def _ev_exact(self, obs_nodes, obs_wires):
r"""Expectation value of observables on specified wires using an exact representation.
Args:
obs_nodes (Sequence[tn.Node]): the observables as TensorNetwork Nodes
obs_wires (Sequence[Wires]): measured wires for each observable
Returns:
complex: expectation value :math:`\expect{A} = \bra{\psi}A\ket{\psi}`
"""
self._contract_premeasurement_network()
ket = self._contracted_state_node
bra = tn.conj(ket, name="Bra")
all_device_wires = Wires(range(self.num_wires))
meas_device_wires = []
# For wires which are measured, add edges between
# the ket node, the observable nodes, and the bra node
for obs_node, wires in zip(obs_nodes, obs_wires):
# translate to consecutive wire labels used by device
device_wires = self.map_wires(wires)
meas_device_wires.append(device_wires)
for idx, l in enumerate(device_wires.labels):
# Use convention that the indices of a tensor are ordered like
# [output_idx1, output_idx2, ..., input_idx1, input_idx2, ...]
output_idx = idx
input_idx = len(device_wires) + idx
tn.connect(obs_node[input_idx], ket[l]) # A|psi>
tn.connect(bra[l], obs_node[output_idx]) # <psi|A
meas_device_wires = Wires.all_wires(meas_device_wires)
# unmeasured wires are contracted directly between bra and ket
unmeasured_device_wires = Wires.unique_wires(
[all_device_wires, meas_device_wires])
for w in unmeasured_device_wires.labels:
tn.connect(bra[w], ket[w])
# At this stage, all nodes are connected, and the contraction yields a
# scalar value.
ket_and_observable_node = ket
for obs_node in obs_nodes:
ket_and_observable_node = tn.contract_between(
obs_node, ket_and_observable_node)
return tn.contract_between(bra, ket_and_observable_node).tensor
def extract_active_wires(self, raw_operation_grid, raw_observable_grid):
"""Get the subset of wires on the device that are used in the circuit.
Args:
raw_operation_grid (Iterable[~.Operator]): The raw grid of operations
raw_observable_grid (Iterable[~.Operator]): The raw grid of observables
Return:
Wires: active wires on the device
"""
# pylint: disable=protected-access
all_operators = list(qml.utils._flatten(raw_operation_grid)) + list(
qml.utils._flatten(raw_observable_grid)
)
all_wires_with_duplicates = [op.wires for op in all_operators if op is not None]
# make Wires object containing all used wires
all_wires = Wires.all_wires(all_wires_with_duplicates)
# shared wires will observe the ordering of the device's wires
shared_wires = Wires.shared_wires([self.wires, all_wires])
return shared_wires
def diagonalize_qwc_pauli_words(qwc_grouping):
"""Diagonalizes a list of mutually qubit-wise commutative Pauli words.
Args:
qwc_grouping (list[Observable]): a list of observables containing mutually
qubit-wise commutative Pauli words
Returns:
tuple:
* list[Operation]: an instance of the qwc_rotation template which
diagonalizes the qubit-wise commuting grouping
* list[Observable]: list of Pauli string observables diagonal in
the computational basis
Raises:
ValueError: if any 2 elements in the input QWC grouping are not qubit-wise commutative
**Example**
>>> qwc_group = [qml.PauliX(0) @ qml.PauliZ(1),
qml.PauliX(0) @ qml.PauliY(3),
qml.PauliZ(1) @ qml.PauliY(3)]
>>> diagonalize_qwc_pauli_words(qwc_group)
([RY(-1.5707963267948966, wires=[0]), RX(1.5707963267948966, wires=[3])],
[Tensor(PauliZ(wires=[0]), PauliZ(wires=[1])),
Tensor(PauliZ(wires=[0]), PauliZ(wires=[3])),
Tensor(PauliZ(wires=[1]), PauliZ(wires=[3]))])
"""
m_paulis = len(qwc_grouping)
all_wires = Wires.all_wires(
[pauli_word.wires for pauli_word in qwc_grouping])
wire_map = {label: ind for ind, label in enumerate(all_wires)}
for i in range(m_paulis):
for j in range(i + 1, m_paulis):
if not is_qwc(
pauli_to_binary(qwc_grouping[i], wire_map=wire_map),
pauli_to_binary(qwc_grouping[j], wire_map=wire_map),
):
raise ValueError(
"{} and {} are not qubit-wise commuting.".format(
qwc_grouping[i], qwc_grouping[j]))
pauli_operators = []
diag_terms = []
paulis_with_identity = (qml.PauliX, qml.PauliY, qml.PauliZ, qml.Identity)
for term in qwc_grouping:
diag_terms.append(diagonalize_pauli_word(term))
if isinstance(term, Tensor):
for sigma in term.obs:
if sigma.name != "Identity":
if not any([
are_identical_pauli_words(sigma, existing_pauli)
for existing_pauli in pauli_operators
]):
pauli_operators.append(sigma)
elif isinstance(term, paulis_with_identity):
sigma = term
if sigma.name != "Identity":
if not any([
are_identical_pauli_words(sigma, existing_pauli)
for existing_pauli in pauli_operators
]):
pauli_operators.append(sigma)
unitary = qwc_rotation(pauli_operators)
return unitary, diag_terms
def _terms_to_qubit_operator(coeffs, ops, wires=None):
r"""Converts a 2-tuple of complex coefficients and PennyLane operations to
OpenFermion ``QubitOperator``.
This function is the inverse of ``_qubit_operator_to_terms``.
Args:
coeffs (array[complex]):
coefficients for each observable, same length as ops
ops (Iterable[pennylane.operation.Observable]): List of PennyLane observables as
Tensor products of Pauli observables
wires (Wires, list, tuple, dict): Custom wire mapping used to convert to qubit operator
from an observable terms measurable in a PennyLane ansatz.
For types Wires/list/tuple, each item in the iterable represents a wire label
corresponding to the qubit number equal to its index.
For type dict, only consecutive-int-valued dict (for wire-to-qubit conversion) is
accepted. If None, will map sorted wires from all `ops` to consecutive int.
Returns:
QubitOperator: an instance of OpenFermion's ``QubitOperator``.
**Example**
>>> coeffs = np.array([0.1, 0.2])
>>> ops = [
... qml.operation.Tensor(qml.PauliX(wires=['w0'])),
... qml.operation.Tensor(qml.PauliY(wires=['w0']), qml.PauliZ(wires=['w2']))
... ]
>>> _terms_to_qubit_operator(coeffs, ops, wires=Wires(['w0', 'w1', 'w2']))
0.1 [X0] +
0.2 [Y0 Z2]
"""
all_wires = Wires.all_wires([op.wires for op in ops], sort=True)
if wires is not None:
qubit_indexed_wires = _process_wires(
wires,
)
if not set(all_wires).issubset(set(qubit_indexed_wires)):
raise ValueError("Supplied `wires` does not cover all wires defined in `ops`.")
else:
qubit_indexed_wires = all_wires
q_op = QubitOperator()
for coeff, op in zip(coeffs, ops):
extra_obsvbs = set(op.name) - {"PauliX", "PauliY", "PauliZ", "Identity"}
if extra_obsvbs != set():
raise ValueError(
"Expected only PennyLane observables PauliX/Y/Z or Identity, "
+ "but also got {}.".format(extra_obsvbs)
)
# Pauli axis names, note s[-1] expects only 'Pauli{X,Y,Z}'
pauli_names = [s[-1] if s != "Identity" else s for s in op.name]
all_identity = all(obs.name == "Identity" for obs in op.obs)
if (op.name == ["Identity"] and len(op.wires) == 1) or all_identity:
term_str = ""
else:
term_str = " ".join(
[
"{}{}".format(pauli, qubit_indexed_wires.index(wire))
for pauli, wire in zip(pauli_names, op.wires)
if pauli != "Identity"
]
)
# This is how one makes QubitOperator in OpenFermion
q_op += coeff * QubitOperator(term_str)
return q_op