# [PhD Thesis Presentation] ‐ Mr. Jiabao Chen -Coherent control of charged particle systems strongly interacting with light

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**Presenter: **Mr. Jiabao Chen

**Title:** Coherent control of charged particle systems strongly interacting with light

**Supervisor:** Professor Denis Konstantinov

**Unit:** Quantum Dynamics

**Co-Supervisor: **Professor Thomas Busch

**Abstract:**

Coherent control of charged particle systems using light is an exciting area of research that can lead to new elements for quantum technologies. However, the choice of a suitable system to realize such applications is limited because of the often unavoidable presence of dissipation and decoherence. One condensed matter system where these problems are minimised is the system of surface electrons on liquid helium. This thesis aims to contribute to achieving coherent control of the quantum states of orbital motion of electrons on helium using quantized electromagnetic field in an optical resonator. In particular, I have studied the strong coupling regime of interaction between the cyclotron motion of electrons and the microwave photons in a Fabry-Perot resonator and provided a detailed analysis of experiments carried out in the Quantum Dynamics Unit at OIST using both classical and quantum formalisms. The agreement between both formalisms demonstrated the mean-value nature of the observed normal mode splitting phenomenon. As a theoretical proposal, I have studied the generation of squeezed states and spin-squeezed states of a harmonic oscillator and of an ensembles of two-level-systems, respectively, which is strongly coupled to a two-level system. In this work I will discuss a special case of the Jaynes-Cummings model driven by an external field and its analogue in which a two-level system is coupled to a collective large spin. This can be seen as a relevant proposal for electrons on helium with coupling between their cyclotron motion and the surface-bound states. Finally, I have studied the surface electrons on helium with a coupling introduced by an in-plane magnetic field. I have shown that this leads to a renormalization of the energy spectrum of coupled orbital motion and have made a number of predictions which were confirmed in a subsequent experiment. This work therefore opens doors to explore the physics in the strong coupling regime between the electrons’ surface-bound states and photons in microwave resonators.

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