Electromagnetically induced transparency for x-rays*

We discuss electromagnetically induced transparency~(EIT) for x-rays in laser-dressed neon. We use a newly devised \emph{ab initio} theory to calculate the x-ray photoabsorption cross section and the x-ray polarizability of a neon atom dressed by an optical laser ($800 \, \mathrm{nm}$, $10^{13} \, \mathrm{\frac{W}{cm^2}}$) with a photon energy close to the $1s^{-1} \, 3s \to 1s^{-1} \, 3p$~transition. The results are investigated further in terms of an exactly solvable $\Lambda$-type three-level model where we point out the need for an intense dressing laser due to the femtosecond lifetime of core-excited neon. Practical experimental realization of EIT for x-rays is discussed and potential applications are outlined. This work opens new opportunities for research with ultrafast x-ray sources.