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Abstract

The direct and optical control of x-ray transitions is studied theoretically by investigating the spectra of resonance fluorescence and absorption. The work is motivated by the rapid advances in x-ray science, enabling the application of quantum-control schemes at short wavelengths. In a two-level system we study Rabi oscillations of atomic inner-shell electrons, induced by intense x-ray pulses and competing with Auger decay, and their signature in the spectrum of resonance fluorescence. Subsequently, optical manipulation of x-ray transitions is examined, by employing an optical frequency comb coupling nearby excited levels to control their spontaneous decay. First, narrow-bandwidth x rays are adopted, giving rise to the periodic shaping of the atomic dynamic variables and the imprinting of a comb onto the x-ray resonance fluorescence spectrum. A more realistic model for an immediate experimental implementation is then provided, by developing a scheme to imprint a comb onto the absorption spectrum of an ultrashort x-ray pulse. An experimental realization of the predicted comb structures is anticipated to transfer the accuracy of optical frequency combs into the x-ray regime.