Attosecond two-photon interferometry for doubly excited states of helium
  We show that the correlation dynamics in coherently excited doubly excited resonances of helium can be followed in real time by two-photon interferometry. This approach promises to map the evolution of the two-electron wave packet onto experimentally easily accessible non-coincident single electron spectra. We analyze the interferometric signal in terms of a semi-analytical model which is validated by a numerical solution of the time-dependent two-electron Schr\"odinger equation in its full dimensionality. 
J. Feist, S. Nagele, C. Ticknor, B. I. Schneider, L. A. Collins, J.   Burgd\"orfer
quant-ph physics.atom-ph