Penning traps, with their ability to control planar crystals of tens to hundreds of ions, are versatile quantum simulators. Thermal occupations of the motional drumhead modes, transverse to the plane of the ion crystal, degrade the quality of quantum simulations. In this talk, I w ill present our theoretical and experimental demonstrations of near ground-state cooling of the drumhead modes of 2D arrays with up to 190 Beryllium ions stored in a Penning trap. This is an order of magnitude increase in the size of an ion crystal that has been ground state cooled. Using the technique of electromagnetically induced transparency (EIT) cooling, we observe simultaneous and substantial sub-Doppler cooling for all the drumhead modes. Quantitative measurements on the highest frequency drumhead mode reveal mean thermal occupations as low as 0.3(0.2) within 200 microseconds. We also measure, rather surprisingly, a cooling rate that is faster than predicted by single particle theory- an observation that is consistent with a quantum many-body calculation. My talk will cover, in equal parts, the theoretical methods used for modeling and interpreting the experiment as well as the experimental techniques, data and inferences.
 E. Jordan, K. A. Gilmore, A .Shankar, A .Safavi-Naini, J. G. Bohnet, M. J. Holland and J. J. Bollinger, arXiv:1809.06346 (2018) (in press, to appear in Phys. Rev. Lett.)
 A. Shankar, E. Jordan, K. A. Gilmore, A. Safavi-Naini, J. J. Bollinger and M. J. Holland, arXiv:1809.05492 (2018) (in press, to appear in Phys. Rev. A)