Entanglement and Coherence in Attosecond Science Experiments

阿秒科学是超快激光物理学的一个分支，旨在通过泵浦-探测实验来研究并可能控制电子在其自然时间尺度上的运动。由高次谐波产生过程形成的阿秒脉冲具有从极端紫外线(XUV)到软X射线光谱范围的波长。因此，阿秒脉冲是对放置在其路径上的任何介质(固体、液体或气体)的电离辐射。正如我的研究小组最近在初步的理论和实验工作中所表明的那样，离子和光电子通常会表现出量子力学纠缠，这会影响阿秒泵浦-探测实验所依赖的相干性。在这里，我提议执行一个项目，通过执行一系列实验，将利用孤立的阿秒激光脉冲的阿秒泵浦-探测光谱与运动学上完整的离子-光电子符合检测相结合，来澄清阿秒分子科学中纠缠和相干之间的关系。据我所知，我在MBI的实验室是目前世界上唯一可以进行孤立阿秒脉冲和符合探测相结合的实验的实验室。更具体地说，在该提案中将进行两项实验。一方面，实验将在H2中进行，在那里孤立的阿秒激光脉冲形成最大纠缠的离子+光电子态。我将研究离子或光电子与近红外探测激光的相互作用如何在离子中诱导电子相干性，这在实验上表现为当阳离子解离时在实验室框架下H+喷射的不对称性。我将探索电子相干性如何依赖于分子相对于激光极化轴和光电子抛射角的排列，并将通过实验研究平均光电子自由度如何导致从“封闭”到“开放”量子系统的转变。另一方面，实验将在氮气中进行，在氮气中，孤立的阿秒激光脉冲的电离将导致几种不同的阳离子状态的形成。这些态处于相干叠加的程度将使用超短(&lt；2fS)紫外激光脉冲的解离来探测，这既是分子相对于激光极化轴的排列和光电子的射出角度的函数。预计阳离子中的电子相干程度，或者相反，离子和光电子之间的纠缠程度将强烈地取决于这些参数。我期待这一提议将导致对纠缠在阿秒科学中的作用的重大澄清，从而将有助于阿秒科学的进一步发展，以充分实现其承诺。

Attosecond science is a branch of ultrafast laser physics that aims to investigate and possibly control electronic motion on its natural timescale by means of pump-probe experiments. Attosecond pulses formed by the process of high-harmonic generation have wavelengths in the extreme ultra-violet (XUV) to soft X-ray spectral range. Accordingly, attosecond pulses are ionizing radiation for any medium (solid, liquid or gaseous) that is placed in its path. As my research group has recently shown in preliminary theoretical and experimental work, the ion and photoelectron will commonly display quantum-mechanical entanglement, which influences the coherence that attosecond pump-probe experiments rely on. Here I propose to perform a project that will clarify the relation between entanglement and coherence in attosecond molecular science, by performing a series of experiments that combine attosecond pump-probe spectroscopy utilizing isolated attosecond laser pulses with kinematically complete ion-photoelectron coincidence detection. To the best of my knowledge, my laboratory at MBI is the only laboratory worldwide where experiments combining isolated attosecond pulses and coincidence detection can currently be performed. More specifically, two experiments will be performed within the proposal. On the one hand, experiments will be performed in H2, where the isolated attosecond laser pulse forms a maximally entangled ion+photoelectron state. I will investigate how interaction of the ion or the photoelectron with a near-infrared probe laser induces electronic coherence in the ion, which experimentally manifests as an asymmetry in the laboratory-frame H+ ejection when the cation dissociates. I will explore how the electronic coherence depends on the alignment of the molecule with respect to the laser polarization axis and the ejection angle of the photoelectron, and will experimentally investigate how averaging over the photoelectron degrees of freedom leads to a transition from a “closed” to an “open” quantum system. On the other hand, experiments will be performed in N2, where ionization by the isolated attosecond laser pulse will lead to the formation of several different cationic states. The degree to which these states are in a coherent superposition will be probed using dissociation by an ultrashort (<2fs) UV laser pulse, both as a function of the alignment of the molecule with respect to the laser polarization axis and the ejection angle of the photoelectron. It is expected that the degree of electronic coherence in the cation, or, conversely, the degree of entanglement between the ion and the photoelectron, will strongly depend on these parameters. I expect that this proposal will lead to significant clarification of the role of entanglement in attosecond science, and thus will contribute to the further development of attosecond science towards full realization of its promise.