Developing Quantum-Optical Measurements of Excitonic Coherence for Quantum Entanglement in Single Organic Molecules

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Organic semiconductors are carbon-based materials that have found widespread use in organic light emitting diodes, solar cells, lasers, and field effect transistors. Excited electronic states in organic semiconductors are delocalised electron hole pairs, called excitons. Very initially these excitons are formed with their partial molecular orbital contributions all perfectly in phase, a quantum mechanically coherent object. Subsequent interactions with the environment dephase the components, collapsing the exciton wavefunction into a classical object. Measurement of this collapse and identifying chemical structures that can preserve coherence long enough for it to be harnessed for quantum entanglement are very challenging.In this proposal novel quantum-optical measurements of excitonic coherence in organic semiconductors will be developed. This will be achieved by measuring the second order photoluminescence intensity cross-correlations in a Hanbury Brown and Twiss geometry of single molecules as a function of energy and time. In doing so, state coupling and state coherences will be measured and chemical structures that can preserve them identified. Two systems will be explored, conjugated molecular dyads where strong coupling exists between the states, and covalently linked dimers where exciton delocalisation occurs over larger distances. The valuable new knowledge that is obtained by working at the single molecule level with novel quantum-optical techniques will realise advances in the fundamental understanding of the nature of excitons, and highlight advantageous ways their properties can be chemically engineered for quantum applications.