Sequential Tunneling vs. Electron Correlation in Multiple   Photo-ionization
  We take advantage of the information provided by use of elliptical polarization in a recent two-electron release time experiment [A.N. Pfeiffer et al., Nature Physics 7, 428 (2011)]. This allows a comparative test of the currently dominant conjectures regarding independent-electron tunneling theory vs. fully electron-correlated classical release theory to describe electron release in strong-field double ionization. 
X. Wang, J. Tian, A. N. Pfeiffer, C. Cirelli, U. Keller, and J. H.   Eberly
physics.atom-ph