Coherent quantum dynamics of cavity-mediated and Forster coupled remote quantum-dot qubits

This project in theoretical physics aims to study the coherent dynamics and resonant Förster transfer of optical excitations (excitons) in single and multiple semiconductor quantum dots (QDs). Such QDs play the role of isolated qubits, and their controlled coupling is of paramount importance for quantum technology applications. Moreover, the study of Förster transfer is highly relevant to understanding the key biological process of photosynthesis on a quantum-mechanical level. Taking inspiration from nature, an enhanced understanding of Förster transfer could enable development of highly efficient artificial light harvesting devices and novel solar cells. The purpose of project includes: (i) an ambitious aim of finding, for the first time, the exact solution for the phonon-assisted exciton Förster transfer between remote, i.e. electronically decoupled QDs; (ii) a study of optical de-coherence and population dynamics in a system of Förster-coupled QDs interacting with the same or different acoustic phonon environment; (iii) a further investigation of how Förster transfer is modified if the QDs are embedded in an optical microcavity and strongly interact with an electro-magnetic cavity mode. Methods: To treat the Förster transfer between QDs coupled to the phonon bath, a novel and powerful approach based on the Trotter decomposition and linked cluster expansion will be used. This approach has been recently developed in the group of Egor Muljarov for obtaining an asymptotically exact solution of the quantum dynamics of a QD-cavity system [1]. Very recently this method has been extended to the non-linear optical response of a QD embedded in a semiconductor micropillar cavity [2,3]. Now this rigorous approach will be applied to new systems of Förster coupled and cavity-mediated coupled QDs. The student will gain knowledge and experience in the areas of many-particle physics, quantum optics and QD-cavity quantum electrodynamics. Various methods of theoretical physics will be employed, including diagram techniques, density matrix approach with Lindblad dissipators, Trotter's decomposition and linked cluster expansion. The project provides a unique opportunity for a theoretically-oriented student to engage with experimental aspects of the field. The project will benefit from a close collaboration with an experimental research team lead by Wolfgang Langbein, possessing a unique experimental technique of heterodyne spectral interferometry for measuring coherence in QD systems. Comparing theory with measured optical data, fundamental mechanisms of the Förster transfer and coherent coupling of QDs will be understood and important parameters of the experimentally investigated systems will be extracted for predictive modelling of QDs embedded in complex quantum circuits.