The main results resulting from this project are:
1) The establishment of a unified theory allowing for the accurate theoretical description of the impact of lattice vibrations on electron-photon coupling in quantum dots embedded in photonic cavities at low temperatures. Using this theory, it has been possible to accurately model leading designs for quantum dot based single photon sources, which are essential components in quantum computing and communication protocols. The results demonstrate that even in photonic cavities, lattice vibrations in quantum dots lead to fundamental limits on the efficiency and indistinguishability of single photons. This result has a wide and substantial impact on quantum dot research, and motivates alternative approaches to combating the effects of thermal excitations in these solid-state systems.
2) The identification of a new mechanism by which lattice vibrations can affect electron-photon coupling in quantum dots at elevated temperatures. Building upon the previous theory, this research found that beyond very low temperatures (10K), lattice vibrations are able to couple to electrons in quantum dots via a new non-linear mechanism, which affects interactions with photons in a quite distinct manner. Importantly, these effects cannot be combated using filtering or optical cavities, and highlights the necessity to work at low temperatures, something that was not previously fully appreciated.
3) The design of a protocol is minimise the impact of coupling to nuclear spins in the generation of electron-photon entanglement. This part of the research designed and analysed a way in which single photons can successively interact with an electron in a quantum dot in such a way as to bypass the effect of coupling to nuclear spins, which would otherwise lead to efficiency and coherence losses. The protocol exploits a mathematical symmetry in the quantum state produced, which effectively decouples the relevant photonic degrees of freedom from the solid-state environment of the quantum dot. This is a significant result, as it indicates that the effects of nuclear spins can be combated without the need to physically manipulate them, leading to a significant reduction in the experimental complexity in producing electron-photon entanglement.
In order to disseminate this research, several publications have been written (see publications tab), while the work has been presented at a number of conferences and workshops, including OECS (Bath, Sept 2017), CLEO Europe (Munich, June 2017), the Quantum Innovators Workshop (Waterloo, October 2016) and Single Photon Single Spin (Oxford, Sept 2016). Furthermore, outreach activities were completed, which were participation in the School of Physics Open Days, the presentation of a display detailing MSCA fellowships at Bristol, and participation in the forthcoming Physics Summer School.
