  Light-induced states are commonly observed in the photoionization spectra of
laser-dressed atoms. The properties of autoionizing polaritons, entangled
states of light and Auger resonances, however, are largely unexplored. We
employ attosecond transient-absorption spectroscopy to study the evolution of
autoionizing states in argon, dressed by a tunable femtosecond laser pulse. The
avoided crossings between the $3s^{-1}4p$ and several light-induced states
indicates the formation of polariton multiplets. We measure a controllable
stabilization of the polaritons against ionization, in excellent agreement with
\emph{ab initio} theory. Using an extension of the Jaynes-Cummings model to
autoionizing states, 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 give new insights into the optical
control of electronic structure in the continuum, and unlock the door to
applications of autoionizing polaritons in poly-electronic systems.

Atomic Physics