Entanglement in helium
  Using a configuration-interaction variational method, we accurately compute the reduced, single-electron von Neumann entropy for several low-energy, singlet and triplet eigenstates of helium atom. We estimate the amount of electron-electron orbital entanglement for such eigenstates and show that it decays with energy. 
Giuliano Benenti, Stefano Siccardi, Giuliano Strini
quant-ph