Controlling photochemistry via quantum superpositions of electronic states: towards attochemistry

在这个项目中，我们将探索-使用计算模拟-激光操纵分子中的电子运动如何提供前所未有的光化学控制。我们试图回答的中心问题是：我们能否通过控制电子态的相干量子叠加在这些态的交叉点附近的初始演化来指导光化学过程的结果？最近，阿秒分子物理学一直在研究“电荷迁移”的概念，即由分子或其他扩展量子系统中的一个电子突然激发而引发的电子动力学。现在很明显，对这种现象的全面解释必须认识到该系统的电子部分和核部分的量子性质。由于演化中的核和电子耦合量子态的相互作用，退相干被发现是异常迅速和普遍的，在迄今研究的所有系统中都发生在几十飞秒的时间尺度上。因此，对光激发量子态动力学的任何控制都只能通过使用在该消相干时间尺度内施加的光场来实现。一个特别重要的目标是控制锥形交叉点附近的超快光场对量子演化的控制。锥形交叉点是势能面的交叉点，在那里非绝热电子-核耦合导致潜在化学路径之间的关键转变。这里的控制最终是对化学结果的控制。使用最先进的代码解决核-电子耦合运动的计算机模拟将被用于预测和解释作为EP/T006943/1的一部分进行的实验。除了为分子的基本行为提供新的见解外，这里发展的超快量子科学可能导致未来的量子设备，其中量子系统内的电荷、能量和信息的流动可以由超快光场控制。

In this project we will explore - using computational simulations - how laser manipulation of electronic motion in molecules might offer unprecedented control over photochemistry. The central question we seek to answer is: can we direct the outcome of a photochemical process by controlling the initial evolution of a coherent quantum superposition of electronic states in the vicinity of a crossing between these states? Recently attosecond molecular physics has been investigating the concept of "charge migration" i.e. electronic dynamics initiated by sudden excitation of an electron in a molecule or other extended quantum system. It is now clear that a full interpretation of such phenomena must recognise the quantum nature of both electronic and nuclear parts of the system. Decoherence due to the interplay of the evolving coupled nuclear and electronic quantum states is found to be exceptionally rapid and general, taking place on a timescale of a few tens of femtoseconds in all systems studied to date. Any control of photoexcited quantum state dynamics can therefore only be achieved by using light fields which are applied within this decoherence timescale. A target of particular significance is the control of quantum evolution by ultrafast light fields in the vicinity of conical intersections: crossings of potential energy surfaces where non-adiabatic electronic-nuclear couplings lead to crucial transitions between potential chemical pathways. Control here is ultimately control of chemical outcomes. Computer simulations using state-of-the-art code to solve the coupled nuclear-electronic motion will be used to predict and explain the experiments carried out as part of EP/T006943/1. As well as providing new insight into the fundamental behaviour of molecules, the ultrafast quantum science developed here may lead to future quantum devices where the flow of charge, energy and information within a quantum system can be controlled by ultrafast light fields.