Coherent control of ionization via stabilization by resonant pulse pairs

We study the nonlinear and resonant process of two-photon ionization of atoms (He and H) in a pump-probe scheme. The pump pulse prepares the quantum system in a superposition of the ground state and an excited bound state. By varying the phase difference between the pulses, we show how it is possible to coherently control the dressed-state population during the probe pulse. Our main result is that for certain laser parameters, the control over the dressed-state population leads to strong control of the ionization probability during the probe pulse. The effect arises due to one of the dressed states becoming stabilized against ionization. Contrasting effects from circular and linear polarized pulses demonstrate how such “bound states in the continuum” are sensitive to the degeneracy of the coupled continuum.