Dr. Peter Asenbaum
Cavity cooling of silicon nanoparticles in high-vacuum
Supervisor: Markus Arndt
Inspired by the successful laser cooling techniques available for atoms, we explore the interaction between nanoparticles and high-finesse optical cavity fields in high-vacuum. The time-dependent forces can create friction, which slows the particle’s motion. We succeeded in demonstrating transverse cavity cooling of silicon nanoparticles in transit through a cavity. Detecting the scattered light from the particle we can trace its motion in real time and obtain detailed insight into the cavity cooling process itself. Laser induced launching techniques eject the particles with forward velocities below 1 m/s resulting in sufficiently long interaction times for cooling. In addition, we were able to prepare and observe freely rotating silicon nanorods. Advancing the current techniques will be crucial for future quantum coherence experiments with nanoparticles.
Dr. Fabio Costa
Local and Causal Structures in Quantum Theory
Supervisor: Caslav Brukner
Quantum mechanics challenges the view that physical properties exist prior to and independent of their observation. Yet, basic notions such as locality or causality are still grounded on a realistic concept of space-time. In my thesis work, the notions of local and causal structures were studied from an operational point of view. During the defence, I will present a new theoretical framework that allows describing multipartite quantum experiments without assuming any underlying space-time. Within this framework, causal relations are not pre-defined, but can be deduced from the possibility of signalling. It is possible to prove that not all situations for which quantum mechanics is locally valid are compatible with a global causal structure. However, if the local validity of classical physics is required instead, a global order follows necessarily. The result suggests that causal order might not be a fundamental property of nature, but rather emerge in a quantum-to-classical transition