  Femtosecond extreme ultraviolet wave packet interferometry (XUV-WPI) was
applied to study resonant inter-atomic Coulombic decay (ICD) in the HeNe dimer.
The high demands on phase stability and sensitivity for vibronic XUV-WPI of
molecular-beam targets are met using an XUV phase-cycling scheme. The detected
quantum interferences exhibit vibronic dephasing and rephasing signatures along
with an ultrafast decoherence assigned to the ICD process. A Fourier analysis
reveals the molecular absorption spectrum with high resolution. The
demonstrated experiment shows a promising route for the real-time analysis of
ultrafast ICD processes with both high temporal and spectral resolution.
