Laurell H, Baños-Gutiérrez J, L'Huillier A, Busto D, Finkelstein-Shapiro D
Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Department of Chemistry, University of California, Berkeley, CA, 94720, USA.
Sci Rep. 2025 Jan 31;15(1):3937. doi: 10.1038/s41598-025-86701-9.
There is a growing interest in reconstructing the density matrix of photoelectron wavepackets, in particular in complex systems where decoherence can be introduced either by a partial measurement of the system or through coupling with a stochastic environment. To this end, several methods to reconstruct the density matrix, quantum state tomography protocols, have been developed and tested on photoelectrons ejected from noble gases following absorption of extreme ultraviolet (XUV) photons from attosecond pulses. It remains a challenge to obtain model-free, single scan protocols that can reconstruct the density matrix with high fidelities. Current methods require extensive measurements or involve complex fitting of the signal. Efficient single-scan reconstructions would be of great help to increase the number of systems that can be studied. We propose a new and more efficient protocol that is able to reconstruct the continuous variable density matrix of a photoelectron in a single time delay scan. It is based on measuring the coherences of a photoelectron created by absorption of an XUV pulse using a broadband infrared (IR) probe that is scanned in time and a narrowband IR reference that is temporally fixed to the XUV pulse. We illustrate its performance for a Fano resonance in He as well as mixed states in Ar arising from spin-orbit splitting. We show that the protocol results in excellent fidelities and near-perfect estimation of the purity.
人们对重建光电子波包的密度矩阵越来越感兴趣，特别是在复杂系统中，在这种系统中，退相干可以通过对系统的部分测量或通过与随机环境耦合来引入。为此，已经开发了几种重建密度矩阵的方法，即量子态层析成像协议，并在从阿秒脉冲吸收极紫外（XUV）光子后从稀有气体中射出的光电子上进行了测试。获得能够以高保真度重建密度矩阵的无模型单扫描协议仍然是一个挑战。目前的方法需要大量测量或涉及信号的复杂拟合。高效的单扫描重建将极大地有助于增加可研究系统的数量。我们提出了一种新的、更有效的协议，该协议能够在单次时间延迟扫描中重建光电子的连续变量密度矩阵。它基于使用随时间扫描的宽带红外（IR）探测器和在时间上固定于XUV脉冲的窄带IR参考来测量由吸收XUV脉冲产生的光电子的相干性。我们展示了它在氦中的法诺共振以及氩中由自旋轨道分裂产生的混合态方面的性能。我们表明，该协议产生了出色的保真度和对纯度的近乎完美的估计。
