Quantum photonics in structured environments

This theoretical PhD project investigates the dynamical properties of quantum emitters interacting with their environment. The contents of the project is divided into two main parts. The first part studies the emission properties of a solid state quantum emitter embedded in a highly structured photonic environment, while interacting with the phonon modes of its constituent lattice. Such a configuration describes a wide range of single-photon sources based on quantum emitters embedded in optical cavities or waveguides. The coupling to phonon modes results in emission of incoherent photons in a broad sideband. However, when the emitter is efficiently interfaced with a highly structured optical environment, the emission properties are strongly altered, and emission of incoherent photons can be suppressed. Such suppression can simultaneously increase the indistinguishability and efficiency of the emitted photons. The second part of the project – carried out in close collaboration with the experimental group of Prof. Mete Atatüre at University of Cambridge – investigates the interaction between a central electron spin and a dense ensemble of nuclear spins. This interaction is found in quantum dots, where a single electron can be trapped by electrically gating the structure. This trapped electron couples to the nuclei of the host lattice, typically on the order of 104 − 105 nuclei, through the magnetic hyperfine interaction. Typically, this interaction is a nuisance, when attempting to control the electron spin, where the nuclear bath acts as a noise source that limits the coherence time. However, this project has contributed to the development of new methods for controlling the nuclear ensemble to an extent that turns it into a resource. In particular, it has been studied how lattice strain breaks the symmetry of the nuclear spins and thereby unlocks a set of low-energy excitations that can be accessed by driving the electron spin. Theoretical models taking this effect into account have been developed and compared to experimental data, demonstrating among other results that the electron spin can be coherently coupled to the collective spin waves in the nuclear bath. Furthermore, a protocol has been developed, which utilises these low-energy excitations to operate the nuclei as a quantum memory for the electron spin.