T. Linowski and Ł. Rudnicki, “Classicality of the Bogoliubov Transformations and the Dynamical Casimir Effect Through the Reduced State of the Field”, Acta Phys. Pol. A, vol. 143, no. 6, p. S95, Jun. 2023, doi: 10.12693/APhysPolA.143.S95.