History-dependent effects in subcycle-waveform strong-field ionization

Recent developments in laser sources allow one to shape the precise electric-field waveform oscillation at the subcycle level. These waveforms may then be used to drive and control ultrafast nonlinear phenomena at the attosecond timescale. By utilizing numerical solutions of time-dependent Schr\"odinger equations and exact solutions of a simple quantum-mechanical system, we show that an atom driven by such sources exhibit coherent history-dependent effects. These manifest themselves in ``macroscopic'' quantities such as the yield in multicolor, strong-field ionization. We argue that weakly bound, metastable electronic states may enable the dependence on the system history even in long-duration, relatively weak driving waveforms.