ISBN 978-3-8439-3596-8

978-3-8439-3596-8, Reihe Physik

Philipp Christoph
Feedback-assisted Sympathetic Cooling in a Hybrid Atomic-mechanical System

179 Seiten, Dissertation Universität Hamburg (2018), Softcover, B5

Zusammenfassung / Abstract

The last decades have seen a tremendous progress in the creation and control of novel quantum systems. As a part of this ongoing research, the field of hybrid quantum systems tries to combine different types of these quantum systems. The combination of their respective advantages offers exciting prospects for new quantum technologies ranging from quantum enhanced sensing to quantum information processing. Furthermore, hybrid quantum systems open the door for fundamental research on emergent phenomena or the universality of quantum mechanics. In sight of these research goals, we have realized a hybrid atomic-mechanical system consisting of a cryogenically cooled membrane oscillator coupled to a cloud of laser cooled rubidium atoms. The longdistance coupling is mediated by a light field and is enhanced by placing the mechanical oscillator inside an optical fiber cavity. This thesis presents details on the experimental setup and the first experiments we have performed in our system. Specifically, the hybrid coupling enables sympathetic cooling of the mechanical oscillator to a minimum mode temperature T = 20 mK through laser cooling of the atoms. In addition to the sympathetic cooling, a setup for active feedback cooling of the oscillator was built up and characterized. The feedback is applied via the radiation pressure of a dedicated laser beam, which is modulated by the homodyne signal of the oscillator. In this way, we achieve a minimum mode temperature of T = 234(42) μK, which corresponds to a thermal mode occupation of n = 18.5(33) phonons. In a further experiment we have demonstrated for the first time the combination of feedback cooling with sympathetic cooling. This proves the technical combinability of feedback cooling with the hybrid coupling mechanism. In the near future, this will enable us to couple a Bose-Einstein condensate to a feedback cooled mechanical oscillator near the quantum ground state. This will be the first realization of a true atomic-mechanical hybrid quantum system.