Abstract In this letter, we will investigate causality in string field theory using pp-wave light-cone gauge string field theory. We will generalise the Ramsey scheme to string field theory, and use it to analyze string field theoretical processes. An explicit characteristic function for interactive string field theory will be built using this string field theoretical Ramsey scheme. The average of the difference between the initial and final values of any operator described in string field theory will be obtained using this characteristic function. We will use the quantum information theoretical technique based on quantum Fisher information to extract information about such string field theoretical processes.