Phase control of the degree of ionization of Rydberg atoms by a strong laser field

It is shown that the rate and degree of ionization of an atom can be controlled by preparing a specific superposition of Rydberg states. This effect is due to the Raman interaction of Rydberg levels via resonant lower-lying levels of the atom. Depending on the initial population of an atom interacting with a strong laser field, the atom either ionizes completely or exhibits an extremely high degree of stability (in this case the probability of the atom remaining in a bound state when the laser pulse is switched off is close to 1). It is shown that states which are stable against ionization decay or, conversely, decay rapidly into the continuum can be prepared using double laser pulses with a controllable time delay