Alternative for Hermitian observable on lightning.gpu device?

PennyLane Help
8

Actually, one alternative might be to do a bit of post-processing. If all you want is the |00…0> coefficient, you can just access it via measuring qml.probs(wires=range(n_qubits)) and accessing the zeroth element:

@qml.qnode(dev_kernel, interface="autograd")
def kernel(x1, x2):
    """The quantum kernel."""
    qml.AmplitudeEmbedding(x1, wires=range(n_qubits), pad_with=2)
    qml.adjoint(qml.AmplitudeEmbedding)(x2, wires=range(n_qubits), pad_with=2)
    return qml.probs(wires=range(n_qubits))

print(kernel([0.1, 0.2], [0.3, 0.4])[0])

Does this fit your needs?