Weak-coupling limits of the quantum Langevin equation for an oscillator

Abstract

The quantum Langevin equation as obtained from the independent-oscillator model describes a strong-coupling situation, devoid of the Born�Markov approximation that is employed in the context of the Gorini�Kossakowski�Sudarshan�Lindblad equation. The question we address is what happens when we implement such �Born�Markov�-like approximations at the level of the quantum Langevin equation for a harmonic oscillator which carries a noise term satisfying a fluctuation�dissipation theorem. In this backdrop, we also comment on the rotating-wave approximation. � 2024 Elsevier B.V.