Return the Pauli sigma_I (identity) operator. The qubit is irrelevant,
    but kept as an  argument for consistency

def sI(qubit: Qubit, coefficient: complex = 1.0) -> Pauli:
    """Return the Pauli sigma_I (identity) operator. The qubit is irrelevant,
    but kept as an  argument for consistency"""
    return Pauli.sigma(qubit, 'I', coefficient)