Quantum entanglement in attosecond ionisation

大约100年前，处于量子力学基础核心的两种量子现象是光电离(爱因斯坦因发现光电效应定律而获得1921年诺贝尔奖)和后来的量子纠缠，量子纠缠导致了著名的爱因斯坦-珀多尔斯基-罗森(EPR)悖论和令人费解的“远距离幽灵作用”概念。这里提出的项目将这两个基本概念结合到一个研究方向，研究超短激光脉冲光离过程中纠缠的形成和控制。这一理论努力显得非常及时，因为最近超快激光技术的发展为实验研究由电离引发的电子运动的最初几飞秒开辟了道路。在大学实验室和世界各地的主要国际激光设施中，使用新一代超快光源执行的时间分辨光谱分析已经可以通过实验获得以前无法观察到的各种光电离物理场景。这些场景涵盖了光-物质相互作用的各种机制，从单光子和多光子微扰到强场非微扰，以及电离光的各种统计特性，从完全相干到随机光脉冲。通过使用量子信息和量子态层析方法，我们的目标是发现发生在阿秒(10^{-18}秒)时间尺度上的电离多电子系统中由量子纠缠支撑的新的物理现象。作为这项研究的一部分，我们将研究光电子和剩余离子之间的量子纠缠，设计光电子的贝尔测试实验来探测这种纠缠，并了解测量对量子多电子动力学的影响。拟议的研究方案将应用我们开发的世界领先的理论和计算工具来研究原子和分子中电荷迁移和其他以前未探索的阿秒尺度过程的性质，包括生物分子的构件。这些工具最初基于费曼对量子力学微扰理论的图解方法，我们将其显著扩展以描述电离电子的大规模运动。作为我们工作的结果，将出现目前缺乏的关于光致电离多体系统中量子纠缠和量子测量效应的图景。从这项研究中获得的知识将导致对物质电子激发的第一时刻的新水平的理解。最终，这可能导致控制辐射损伤过程的新方法，对放射生物学和最终对放射治疗产生直接影响。例如，已经证明，在物质的关键分子构件中的电子激发之后，伴随着一个普遍的初级事件--电荷跨越纳米的亚飞秒到几飞秒的迁移。这种电荷迁移预计将对触发随后的核动力学极其重要，从而最终控制已被称为“原子化学”的化学变化。

Two of the quantum phenomena at the very heart of the foundation of quantum mechanics, as it emerged about 100 years ago, were photoionisation (Einstein's 1921 Nobel prize for the discovery of the law of the photoelectric effect) and later on quantum entanglement, which led to the famous Einstein-Podolsky-Rosen (EPR) paradox and the puzzling concept of 'spooky action at a distance'.The project proposed here joins these two fundamental concepts into a single research direction studying the formation and control of entanglement in photoionisation by ultra-short laser pulses. This theoretical endeavour emerges as very timely due to the recent developments in ultrafast laser technology that have opened the way to the experimental study of the very first few femtoseconds of the motion of electrons triggered by ionisation. A wide range of physical scenarios of photoionisation that previously could not be observed as they evolve in time, have become experimentally accessible to time-resolved spectroscopy performed with the new generation ultrafast light sources at both university laboratories and the major international laser facilities around the world. These scenarios encompass various regimes of the light-matter interaction, from the single- and multi-photon perturbative one to the strong-field non-perturbative one, as well as various statistical properties of the ionising light, from fully coherent to stochastic light pulses. By using quantum information and quantum state tomography approaches, we aim to discover new physical phenomena underpinned by quantum entanglement in ionising many-electron systems, occurring on the attosecond (10^{-18} of a second) time scale. As part of this research, we will study quantum entanglement between the photoelectron and the remaining ion, devise Bell-test experiments with photoelectrons to probe this entanglement and find out about the effect of measurement on the quantum many-electron dynamics. The proposed research programme will apply the world-leading theoretical and computational tools we developed to study the nature of charge migration and other previously unexplored attosecond-scale processes in atoms and molecules, including the building blocks of biomolecules. These tools, originally based on Feynman's diagrammatic approach to quantum mechanical perturbation theory, are significantly extended by us to describe the large-amplitude motion of the ionised electron. As a result of our work, there will emerge the presently lacking picture of the effect of quantum entanglement and quantum measurement in photo-ionised many-body systems. The knowledge gained from this research will lead to a new level of understanding of the first moments in the electronic excitation of matter. Ultimately, this may lead to new ways to control the radiation damage processes, with direct implications on radiobiology and eventually on radiotherapy. For instance, it has been shown that electronic excitation in key molecular building blocks of matter is followed by a universal primary event - sub-femtosecond to few femtosecond migration of electric charge across nanometres. This charge migration is expected to be extremely important for triggering the subsequent nuclear dynamics and therefore ultimately controlling the chemical change in what has become known as "attochemistry".