Cooperative effects in opto- and nanomechanics

Abstract

This thesis presents works in optomechanics which describes the interaction of electromagnetic radiation with massive objects through radiation pressure. As this force is extremely minute, the mechanical objects that can be influenced through this effect need to possess so little mass that the system enters the realm of quantum mechanics and requires an appropriate quantum mechanical treatment. Additionally, the physical phenomena that occur through radiation pressure can be amplified through application of large power where non-linear forces determine the system’s dynamics. This thesis aims to combine the strengths and opportunities that nonlinearity and quantum mechanical aspects offer for future technological applications incorporating many constituents. Symmetries of many body systems are ubiquitous and offer a way to classify the macroscopic features of a system. It is the spontaneous breaking of a symmetry which occurs during a plethora of phase transitions and which enables to distinguish distinct macroscopic phases of matter. In this thesis we study and discover exotic phases of optomechanical arrays resulting from exchange symmetries which are the building block in non-linear pattern formation and stable signal generation. We show that through specific periodic modulation of the interaction the stability of these signals can be extended to distinct frequencies. Through our collaboration its experimental realisation proves the long-term frequency stability to be significantly improved with this mode-locking mechanism. This result is a key ingredient enabling highly stable ultracompact oscillators, coherent waveform synthesis, pulsed phonon lasing, and other many-mode phenomena in oscillator arrays. Inspired through these results we discover another scheme to employ distinct mechanical modes to steer between distinct steady states induced by changes of radiation pressure in a cavity. Additionally, we find that thermal effects have a significant influence which can suppress or even amplify the control mechanism despite its usually performance-limiting character. The modulation scheme offers techniques for the characterisation of these thermal properties in optomechanical systems as well as their control, sensing and computational applications.