近日，瑞士保罗·谢勒研究所Gregor Knopp团队研究了核-壳层电子的相干非线性X射线四光子相互作用。2026年1月14日，《自然》杂志发表了这一成果。

相干非线性X射线-物质相互作用为超快光谱学研究开辟了新领域，实现了原子级空间分辨率与飞秒-阿秒时间尺度的结合。其中，X射线四波混频技术通过单个相干非线性过程包含多个共振跃迁，有望以态选择性和位点选择性方式揭示电子态耦合、相干电子运动、关联效应及动力学特征。

研究组利用自由电子激光产生的宽带单脉冲X射线，实现了与核壳电子的相干、无背景四光子相互作用。在气态氖中观测到的全X射线四波混频信号来源于包含拉曼跃迁的双共振非线性过程，其中包含X射线相干反斯托克斯电子拉曼散射。通过获取二维（光子输入/光子输出）光谱图，研究组向原子尺度的多维关联光谱学迈出了关键一步。进一步采用多色时间延迟X射线脉冲方案，证实了将该方法拓展至超快时间域的可行性。这些成果揭示了该方法在研究生物分子至关联量子材料等多种体系中局域电子动力学的潜力，在能量转换、生物医学成像及量子信息技术等领域具有重要应用前景。

附：英文原文

Title: Coherent nonlinear X-ray four-photon interaction with core-shell electrons

Author: Morillo-Candas, Ana Sofia, Augustin, Sven, Prat, Eduard, Sarracini, Antoine, Knurr, Jonas, Zerdane, Serhane, Sun, Zhibin, Yang, Ningchen, Rebholz, Marc, Zhang, Hankai, Deng, Yunpei, Xie, Xinhua, Zyaee, Elnaz, Rohrbach, David, Cannizzo, Andrea, Al-Haddad, Andre, Schnorr, Kirsten, Ott, Christian, Feurer, Thomas, Bostedt, Christoph, Pfeifer, Thomas, Knopp, Gregor

Issue&Volume: 2026-01-14

Abstract: Coherent nonlinear light–matter interaction with X-rays gives access to a regime in ultrafast spectroscopy in which atomic resolution meets femtosecond and attosecond timescales1,2. Particularly, X-ray four-wave mixing, involving several resonant transitions in a single coherent nonlinear process, has the potential to provide information on the electronic states coupling, coherent electron motion, correlation and dynamics, with state and site selectivity3,4,5. Here we demonstrate coherent, background-free four-photon interactions with core-shell electrons using single broadband X-ray pulses from a free-electron laser. The all-X-ray four-wave mixing signals, measured in gaseous neon, arise from doubly resonant nonlinear processes involving Raman transitions6, including X-ray coherent anti-Stokes electronic Raman scattering. The 2D spectral maps (photon-in/photon-out) represent a step towards multidimensional correlation spectroscopy at the atomic scale. Using a multicolour time-delayed X-ray pulse scheme, we further demonstrate the feasibility of extending the proposed methodology to the ultrafast time domain. These results reveal potential for studying localized electron dynamics in multiple systems, from biomolecules to correlated quantum materials, with applications in areas such as energy conversion, biomedical imaging and quantum information technologies.

DOI: 10.1038/s41586-025-09911-1

Source: https://www.nature.com/articles/s41586-025-09911-1