Attosecond Correlated Dynamics of Two Electrons Passing through a Transition State

The strong-field induced decay of a doubly excited, transient Coulomb complex Ar** -> Ar2+ + 2e(-) is explored by tracing correlated two-electron emission in nonsequential double ionization of Ar as a function of the carrier-envelope phase. Using <6 fs pulses, electron emission is essentially confined to one optical cycle. Classical model calculations support that the intermediate Coulomb complex has lost memory of its formation dynamics and allows for a consistent, though model-dependent definition of emission time, empowering us to trace transition-state two-electron decay dynamics with sub-fs resolution. We find a most likely emission time difference of similar to 200 +/- 100 as.