Public defence in Engineering Physics, M.Sc. Juuso Manninen

Accessing quantum phenomena using mechanical resonators

Title of the doctoral thesis is Interference, noise, and correlation phenomena in quantum devices

Quantum optomechanics is a branch of physics that focuses on the study of the interaction between light and mechanically vibrating objects. The radiation pressure caused by light is a very weak phenomenon and, therefore, it is not familiar from every-day experience. For example, you cannot detect the recoil of turning a flashlight on with your own eyes. In research use, this phenomenon can be utilized, for example, in extremely precise position measurements, like the famous LIGO experiments where gravitational waves were observed in 2016.

Due to the weakness of the radiation pressure, it is vital to understand the disturbances caused by the environment in real measurements and possible future applications. In the thesis study, the influence that atomic scale impurities, commonly hidden in low temperature measurement setups, have on the behavior of an optomechanical system is theoretically investigated to understand their contribution to the noise in practical measurements. Additionally, an experimental setup demonstrating a significant increase in the strength of the radiation pressure interaction is presented in the study. A very strong interaction would enable future studies investigating the quantum mechanical nature of mechanical resonators and would shed light on the boundary between classical and quantum realms.

The quantum mechanical properties of mechanical resonators can also be accessed in an optomechanical Bell test scheme proposed in the study. Bell inequalities describe boundaries for correlations seen in measurements that can be broken only if the studied system exhibits quantum mechanical behavior. The study showed theoretically how, in an optomechanical experimental setup, a mechanical resonator can create nonclassical correlations in the light interacting with it.

Mechanical motion was also utilized to study the magnetic properties of graphene, a two-dimensional form of carbon. In a magnetic field, the electrons in a graphene conductor can settle to certain quantized energy levels. In the measurements, de Haas–van Alphen effect arising from the quantized energy levels was detected by monitoring the resonance frequency of a graphene-gold resonator. This study gained new information on the magnetization of graphene, and the new measurement scheme using the motion of a graphene-gold system could be extended to study magnetization in other two-dimensional conductors.

Opponent is Professor Klemens Hammerer, Leibniz University of Hannover, Germany

Custos is Professor Pertti Hakonen, Aalto University School of Science, Department of Applied Physics

Contact details of the doctoral student: [email protected]

The public defence will be organised in Otaniemi (Otakaari 1, lecture hall M1).

The dissertation is publicly displayed 10 days before the defence in the publication archive Aaltodoc of Aalto University

Electronic thesis

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