qml.expval

expval(op)[source]

Expectation value of the supplied observable.

Example:

dev = qml.device("default.qubit", wires=2)

@qml.qnode(dev)
def circuit(x):
    qml.RX(x, wires=0)
    qml.Hadamard(wires=1)
    qml.CNOT(wires=[0, 1])
    return qml.expval(qml.PauliY(0))

Executing this QNode:

>>> circuit(0.5)
-0.4794255386042029
Parameters

op (Union[Observable, MeasurementValue]) – a quantum observable object. To get expectation values for mid-circuit measurements, op should be a MeasurementValue.

Returns

measurement process instance

Return type

ExpectationMP

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