EPL, vol.139, no.4, 2022 (SCI-Expanded)
Copyright © 2022 EPLA.In this paper, we analyze the evolution of physical quantities due to the interaction of strings with background fields. We will obtain the characteristic function for such a string theoretical process. This will be done by generalizing the Ramsey scheme to world-sheet, and using it to obtain the information about the evolution of quantity in a string theoretical process, without making two-point measurements. We will also use the characteristic function to obtain the average of the difference between the initial and final values of such a quantity. Finally, using the characteristic function, we calculate the Fisher information for the difference of such a quantity. ©