Probing and controlling autoionizing polaritons in atomic ionization

Theoretical studies of laser dressed autoionizing states have predicted control and stabilization against ionization under specific conditions. Here we use attosecond extreme ultraviolet transient absorption spectroscopy to investigate the evolution of autoionizing states in argon atom dressed by a tunable femtosecond IR laser pulse. We observe avoided crossings between the 3s$^{-1}$4p and several light-induced states, indicating the formation of polaritons.  The properties of these autoionizing polaritons, entangled states of light and Auger resonances are largely unexplored. We show evidence of stabilization of the polaritons against ionization by using time-delay, frequency detuning, and laser intensity as control parameters. The experimental results match well with ab-initio theoretical calculations. We show that this stabilization is due to the destructive interference between the Auger decay and the radiative ionization of the polaritonic components. These results open the doors for optical control of continuum states in polyelectronic systems.