qml.var

var(op: pennylane.operation.Operator)[source]

Variance of the supplied observable.

Parameters

op (Observable) – a quantum observable object

Returns

measurement process instance

Return type

VarianceMP

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.var(qml.PauliY(0))

Executing this QNode:

>>> circuit(0.5)
0.7701511529340698

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