def __init__(self, qubits, observable=Observable.Z()):
"""
- qubit (int): The index of the qubit
- observable=Observable.Z() (matrix, tuple, or QNN-Gen Observable object): The observable
to meausre with respect to
- If matrix it should be a list or numpy.ndarray
- If tuple, it should be of the form ("name": matrix)
"""
if isinstance(qubits, int):
self.qubits = [qubits]
else:
self.qubits = qubits # just single-qubit for now
if isinstance(observable, (list, np.ndarray)):
self.observable = Observable(observable)
elif isinstance(observable, tuple):
self.observable = Observable(matrix=observable[1],
name=observable[0])
elif isinstance(observable, Observable):
self.observable = observable
else:
raise ValueError(
"Observable argument is not a correct type. Check the __init__ docstring."
)
if self.observable.name == "Z":
requires_rotation = False
else:
requires_rotation = True
super().__init__(qubits=self.qubits, rotate=requires_rotation)
def default_measurement(self, observable=None, measurement_qubit=None):
"""
Default measurement is the Z expectation of the measurement_qubit
Inputs:
- observable=None [Observable]: If None, defaults to Observable.Z()
- measurement_qubit [int]: If None, defaults to self.measurement_quibt = n_qubits//2
Returns:
- Expectation() measurement object
"""
from Observable import Observable
from Measurement import Expectation
if observable is None:
observable = Observable.Z()
if measurement_qubit is None:
measurement_qubit = self.measurement_qubit
expectation = Expectation(measurement_qubit, observable)
return expectation
