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

有机半导体是碳基材料，广泛应用于有机发光二极管、太阳能电池、激光器和场效应晶体管。有机半导体中的激发态是离域电子空穴对，称为激子。最初，这些激子形成时，它们的部分分子轨道贡献都是完全一致的，是一个量子力学相干的物体。随后与环境的相互作用使元件失相，将激子波函数坍缩为经典对象。测量这种坍缩并确定能够保持足够长时间的相干性以用于量子纠缠的化学结构是非常具有挑战性的。在本提案中，将发展有机半导体中激子相干性的新型量子光学测量。这将通过测量单分子的Hanbury Brown和Twiss几何结构中作为能量和时间函数的二阶光致发光强度相互关系来实现。在此过程中，将测量状态耦合和状态相干，并确定能够保持它们的化学结构。将探索两种系统，共轭分子二偶体，其中状态之间存在强耦合，共价连接二聚体，其中激子离域发生在更大的距离上。利用新颖的量子光学技术在单分子水平上获得的有价值的新知识将实现对激子本质的基本理解的进步，并突出其性质可以用于量子应用的化学工程的有利方法。

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.