Watching the quantum race of electrons

When a photon of sufficient high energy hits an atom it may kick out an electron. Quantum mechanics predicts that the electron behaves like a wave that runs away from the atom. If the photon energy was chosen right then a second electron (Auger electron) may be liberated from the atom, racing behind the first one. We were able to detect how this second electron overtakes the first one within only a few femtoseconds (1 fs = 10-15 seconds) and observe the dynamic exchange of energy between the two electrons when they are passing each other.