def apply_controlled_Q(fn, wires, target_wire, control_wire, work_wires):
r"""Provides the circuit to apply a controlled version of the :math:`\mathcal{Q}` unitary
defined in `this <https://arxiv.org/abs/1805.00109>`__ paper.
The input ``fn`` should be the quantum circuit corresponding to the :math:`\mathcal{F}` unitary
in the paper above. This function transforms this circuit into a controlled version of the
:math:`\mathcal{Q}` unitary, which forms part of the quantum Monte Carlo algorithm. The
:math:`\mathcal{Q}` unitary encodes the target expectation value as a phase in one of its
eigenvalues. This phase can be estimated using quantum phase estimation (see
:class:`~.QuantumPhaseEstimation` for more details).
Args:
fn (Callable): a quantum function that applies quantum operations according to the
:math:`\mathcal{F}` unitary used as part of quantum Monte Carlo estimation
wires (Union[Wires or Sequence[int]]): the wires acted upon by the ``fn`` circuit
target_wire (Union[Wires, int]): The wire in which the expectation value is encoded. Must be
contained within ``wires``.
control_wire (Union[Wires, int]): the control wire from the register of phase estimation
qubits
work_wires (Union[Wires, Sequence[int], or int]): additional work wires used when
decomposing :math:`\mathcal{Q}`
Returns:
function: The input function transformed to the :math:`\mathcal{Q}` unitary
Raises:
ValueError: if ``target_wire`` is not in ``wires``
"""
fn_inv = adjoint(fn)
wires = Wires(wires)
target_wire = Wires(target_wire)
control_wire = Wires(control_wire)
work_wires = Wires(work_wires)
if not wires.contains_wires(target_wire):
raise ValueError("The target wire must be contained within wires")
@wraps(fn)
def wrapper(*args, **kwargs):
_apply_controlled_v(target_wire=target_wire, control_wire=control_wire)
fn_inv(*args, **kwargs)
_apply_controlled_z(wires=wires,
control_wire=control_wire,
work_wires=work_wires)
fn(*args, **kwargs)
_apply_controlled_v(target_wire=target_wire, control_wire=control_wire)
fn_inv(*args, **kwargs)
_apply_controlled_z(wires=wires,
control_wire=control_wire,
work_wires=work_wires)
fn(*args, **kwargs)
return wrapper
def test_contains_wires(self, ):
"""Tests the dedicated contains_wires() method."""
wires = Wires([0, 1, 2, 3, Wires([4, 5]), None])
assert wires.contains_wires(Wires([0, 3]))
assert wires.contains_wires(Wires([1, 2, None]))
assert wires.contains_wires(Wires([Wires(
[4, 5])])) # Wires([4, 5]) is just a label!
assert not wires.contains_wires(0) # wrong type
assert not wires.contains_wires([0, 1]) # wrong type
assert not wires.contains_wires(Wires(
[4, 5])) # looks up 4 and 5 in wires, which are not present
