标题： 超快瞬态吸收光谱中的分子轴分布矩：通往超快量子态层析成像之路 显示英文标题

标题： Molecular Axis Distribution Moments in Ultrafast Transient Absorption Spectroscopy: A Path Towards Ultrafast Quantum State Tomography

摘要： 在气相分子的超快实验中，分子轴相对于相互作用激光脉冲偏振方向的排列在确定光与物质相互作用后的动力学过程中起着至关重要的作用。 分子轴分布受到相互作用脉冲的影响，并且本质上与激发分子的电子相干性相关联。 然而，在此类相互作用的典型理论计算中，信号要么是针对分子坐标系中的单个分子计算的，要么是在所有可能的分子取向上平均以与实验进行比较。 这种平均导致了关于分子轴分布各向异性的信息丢失，这可能会显著影响所测量的实验信号。 在这里，我们用分离的分子坐标系和实验室坐标系量来计算实验室坐标系下的瞬态电子一阶极化（$P^{(1)}$）光谱。 实验室坐标系下的极化与取向平均的量子主方程 (QME) 计算结果进行了比较，证明了取向平均仅捕捉到了各向同性贡献。 我们展示了我们的方法还可以评估光谱的各向异性贡献。 最后，我们讨论了这种方法在利用瞬态吸收光谱和非线性光谱中的场可观测量实现超快量子态层析成像方面的应用。 显示英文摘要

摘要： In ultrafast experiments with gas phase molecules, the alignment of the molecular axis relative to the polarization of the interacting laser pulses plays a crucial role in determining the dynamics following this light-matter interaction. The molecular axis distribution is influenced by the interacting pulses and is intrinsically linked to the electronic coherences of the excited molecules. However, in typical theoretical calculations of such interactions, the signal is either calculated for a single molecule in the molecular frame or averaged over all possible molecular orientations to compare with the experiment. This averaging leads to the loss of information about anisotropy in the molecular-axis distribution, which could significantly affect the measured experimental signal. Here, we calculate the laboratory frame transient electronic first-order polarization ($P^{(1)}$) spectra in terms of separated molecular frame and laboratory frame quantities. The laboratory frame polarizations are compared with orientation-averaged Quantum Master Equation (QME) calculations, demonstrating that orientation-averaging captures only the isotropic contributions. We show that our formalism allows us to also evaluate the anisotropic contributions to the spectrum. Finally, we discuss the application of this approach to achieve ultrafast quantum state tomography using transient absorption spectroscopy and field observables in nonlinear spectroscopy.