Extreme-ultraviolet frequency-comb spectroscopy

The spectroscopic study of simple atoms has played an important role in the development of quantum mechanics. The energy levels of hydrogen-like atoms can be accurately described by bound-state quantum electro- dynamics (QED). As an example, the 1s-2s transition of atomic hydrogen has been measured with a relative uncertainty of 10-15 and compared with QED prediction, which serves as a stringent test of QED. Another interesting target is hydrogen-like He+ ions. He+ has twice larger nuclear charge than hydrogen and therefore high-order QEQ-contributions are enhanced. We plan to perform a spectroscopy on He+ 1s-2s transition at 61 nm by utilizing extreme-ultraviolet (EUV) frequency combs. The target He+ ions will be trapped in the Paul trap in order to achieve the long interaction time with the spectroscopy laser and also to suppress systematic effects. In this talk, our recent progress on EUV frequency comb generation and He+ ion trap setup will be presented.
We discuss here first the out of equilibrium dynamics of spin and density degrees of freedom following a quench in one dimension. Using spin-resolved quantum gas microscopy we directly observe the spin-charge deconfinement dynamics after the removal of one fermion from the Hubbard chain.
We then contrast these results with the measurement of equilibrium correlations in particle-doped twodimensional Hubbard systems. We detect here a local reduction of the spin correlations in the direct vicinity of the double occupancies. We interpret it as the dressing cloud of a magnetic polaron and demonstrate that it originates from the competition between kinetic and magnetic energy.