Effcient sympathetic cooling in mixed barium and ytterbium ion chains.

We Doppler cool barium ions in mixed barium-ytterbium chains confined in a linear RF trap and measure the motional average occupation quantum numbers of all radial normal modes. The full set of orderings in a chain of two barium and two ytterbium ions have been probed, and we show that the average thermal occupation number for all chain configurations strongly depends on the trap aspect ratio. We demonstrate efficient sympathetic cooling of all radial normal modes for the trap aspect ratio of 2.9.