Real-time observation of valence electron motion in krypton atoms is achieved using attosecond pump-probe spectroscopy. The study reveals the subfemtosecond dynamics of valence electrons in krypton ions, which are generated by a controlled few-cycle laser field. The ions are probed using an attosecond extreme-ultraviolet (EUV) pulse, allowing the observation of electronic coherence and wave-packet motion over a multifemtosecond timescale. The results show that strong-field ionization can create a broadband valence electron wave packet with high coherence, persisting for more than 10 fs. The study demonstrates that attosecond transient absorption spectroscopy can reveal the electronic dynamics of molecules and solid-state materials, providing insights into the fundamental processes that govern physical, chemical, and biological properties. The research highlights the importance of electronic coherence in real-time observation of electron motion and shows that few-cycle ionization can generate robust electronic coherence. The findings have implications for understanding the dynamics of electron wave packets in atoms, molecules, and solids, and could lead to new methods for studying electronic processes in materials. The study also addresses the limitations of current experimental techniques in probing all degrees of freedom in open systems and emphasizes the need for further theoretical development to fully exploit the potential of attosecond spectroscopy. The results are supported by detailed simulations and experimental data, demonstrating the feasibility of real-time observation of electronic processes at the atomic scale.Real-time observation of valence electron motion in krypton atoms is achieved using attosecond pump-probe spectroscopy. The study reveals the subfemtosecond dynamics of valence electrons in krypton ions, which are generated by a controlled few-cycle laser field. The ions are probed using an attosecond extreme-ultraviolet (EUV) pulse, allowing the observation of electronic coherence and wave-packet motion over a multifemtosecond timescale. The results show that strong-field ionization can create a broadband valence electron wave packet with high coherence, persisting for more than 10 fs. The study demonstrates that attosecond transient absorption spectroscopy can reveal the electronic dynamics of molecules and solid-state materials, providing insights into the fundamental processes that govern physical, chemical, and biological properties. The research highlights the importance of electronic coherence in real-time observation of electron motion and shows that few-cycle ionization can generate robust electronic coherence. The findings have implications for understanding the dynamics of electron wave packets in atoms, molecules, and solids, and could lead to new methods for studying electronic processes in materials. The study also addresses the limitations of current experimental techniques in probing all degrees of freedom in open systems and emphasizes the need for further theoretical development to fully exploit the potential of attosecond spectroscopy. The results are supported by detailed simulations and experimental data, demonstrating the feasibility of real-time observation of electronic processes at the atomic scale.