Advances in laser pump-probe techniques open the door for observations in real time of ultrafast electronic processes. Particularly attractive is the visualization of interatomic processes where one can follow the energy transfer from one atom to another. The interatomic Coulombic decay (ICD) provides such a process which is abundant in nature. A wave packet propagation method now enables us to trace fully ab initio the electron dynamics of the process in real time and space, taking into account all electrons of the system and their correlations. The evolution of the electronic cloud during the ICD process in NeAr following $\mathrm{Ne}2s$ ionization is computed and analyzed. The process takes place on a femtosecond time scale, and a surprisingly strong response is found already in the attosecond regime.

• Received 28 August 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.083201