Anisotropy Induced Electronic Coherence Signal in Attosecond Transient Absorption Spectroscopy*

Probing electronic coherence in molecules is essential for controlling chemical reactivity.  Although attosecond transient absorption spectroscopy (ATAS) has been a prominent method for probing electronic coherence, how the intense pump laser creates the coherence in molecules is not well understood due to the computational challenges of simulating strong-field processes. Using a density matrix approach recently developed by our group [1, 2], we demonstrate that the emergence of coherent ATAS signals in nitrogen molecular ions critically depends on the anisotropy induced by strong-field ionization [3]. This work highlights that the density matrix approach can be integrated with more accurate quantum chemistry methods to describe the creation, evolution, and detection of electronic coherence in molecules. It also motivates further development in first-principles approaches to obtain orientation-dependent density matrices for the electronic states of molecular ions created by strong laser pulses. Lastly, we call for future ATAS experiments to validate our findings.

[1] Yuen and Lin, Phys. Rev. A 108, 023123 (2023)

[2] Yuen and Lin, Phys. Rev. A 109, 033108 (2024)

[3] Yuen and Lin, Commun. Phys. 7, 115 (2024)