On the problem of the back-reaction in optomechanics and analog models

The problem of the back-reaction (BR) has its roots in the field of gravity but, nevertheless, is a general concept and relevant to a wide range of physical systems. It aims towards a self-consistent theory of the interaction between a quantum field and its background.

We pursue the study of the BR within the framework of optomechanics and analog models. (i) In the former case, we consider an optical cavity enclosed by a freely moving mirror. In this case the BR is exerted onto the moving mirror by the particles created in the cavity because of the dynamic Casimir effect. This results in an effective damping experienced by the mirror. We investigate the quantum fluctuations of such friction force, as well as their consequences on the quantum state of the mirror. (ii) In the latter case, a time dependent background is implemented by considering a non-stationary Bose-Einstein condensate (BEC). We simulate the phenomenon of the Pre-Heating in the early Universe by using an elongated condensate, that is let to oscillate in its transverse direction by exciting one (or more) of the corresponding (high-energy) modes. We observe the amplification of the vacuum fluctuations in the (low-energy) longitudinal modes and the damping of the transverse modes.