Master thesis defense by Emil Zeuthen – Niels Bohr Institute - University of Copenhagen

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Master thesis defense by Emil Zeuthen

Recent experimental advances in the field of cavity mechanics have led to unprecedented control over macroscopic mechanical oscillators by means of coupling to an optical or electrical cavity. Specifically, efficient resolved-sideband cooling of the mechanical center-of-mass motion has been achieved, potentially allowing for quantum control of macroscopic objects. 

The thesis consists of two subprojects: 

“Framework for electromechanical coupling calculations” - we establish a quantum description for the electromechanical interaction between a vibrating membrane and a capacitive element of an electric circuit. The approach presented here allows for manageable numerical calculation of the coupling parameters for given geometry and materials choice while capturing the essential features of the setup. Such a method may well be valuable in developing and engineering the electromechanical links that have been envisioned to participate in larger cavity-mechanical setups [1]. The method is demonstrated by application to a current experimental project. 

“Extending cavity-mechanical cooling via a hot LC circuit” - we explore schemes for extending the successful technique of cavity-mechanical single-mode cooling by coupling to additional objects [1]. We consider a new, indirect scheme involving a rapidly decaying link mode that mediates the cooling from the mechanical mode to a weakly coupled but long-lived target system. By optimizing this scheme we arrive at the surprising result that it is possible to cool the target system even under circumstances where it is impossible to cool the link mode significantly. This phenomenon may be understood in terms of interference and points toward new ways of thinking about and utilizing single-mode cooling. Possible implementations of the scheme will be discussed briefly. 

[1] J. M. Taylor, A. S. Sørensen, C. M. Marcus, and E. S. Polzik. Laser cooling and optical detection of excitations in a LC electrical circuit. Phys. Rev. Lett., 107:273601, 2011.