“…However, in the scientific literature, we can find proposals that treat the external degrees of freedom (EDF) as a quantum variable giving a quantum description of the evolution of the EDF; see [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 13 ]. Nevertheless, in a recent paper, we gave a complete quantum treatment of the SGE [ 5 , 6 ], as it was originally thought of by Scully et al [ 9 ], by using the evolution operator method [ 21 , 22 , 23 , 24 , 25 ] and obtaining the solution to the Schrödinger equation; this allows us to see the quantum features of the EDF. It is worth mentioning that in Figure 1 of [ 5 ], we are replacing the usual continuous path by a dotted one to stress the absence of classical paths.…”