Prospects for quantum simulations with mixed species crystals in Penning traps

Penning traps are now an established platform for quantum science experiments with tens to hundreds of ions. Such experiments have typically employed a single trapped ion species. The inclusion of multiple ion species can lead to the emergence of novel crystal geometries and normal mode properties that may enable new classes of quantum science experiments in Penning traps. In this work, we study the equilibrium structure and normal modes of crystals formed by two species of ions co-trapped in a Penning trap. We observe that, under specific conditions, the ions organize into a 2D planar crystal, with the heavier ions forming a clean, well-separated ring at the crystal boundary. This finding opens avenues for studying spin models with closed and periodic boundary conditions. When the trapping conditions are scanned across the one-to-two plane transition point, the lighter ions in the crystal interior form a 3D crystal, while the heavier ions can still be confined to a planar ring. Under these conditions, some of the axial normal modes of the ring acquire a chiral nature, potentially enabling interesting opportunities for quantum simulations. Finally, the addition of an anharmonic trapping potential leads to all the lighter ions forming a clean bilayer geometry, which is stabilized by the ring of heavier mass ions. Our study demonstrates the potential for diversifying quantum simulation applications of Penning traps by utilizing more than one species of ions.