Prepare a 16-qubit W state using sqrt(iswaps) and local gates,
    respecting linear topology

def prepare_w16():
    """
    Prepare a 16-qubit W state using sqrt(iswaps) and local gates,
    respecting linear topology

    """
    ket = qf.zero_state(16)
    circ = w16_circuit()
    ket = circ.run(ket)
    return ket