  We investigate the dynamics of mixed-species ion crystals during transport
between spatially distinct locations in a linear Paul trap in the diabatic
regime. In a general mixed-species crystal, all degrees of freedom along the
direction of transport are excited by an accelerating well, so unlike the case
of same-species ions, where only the center-of-mass-mode is excited, several
degrees of freedom have to be simultaneously controlled by the transport
protocol. We design protocols that lead to low final excitations in the
diabatic regime using invariant-based inverse-engineering for two
different-species ions and also show how to extend this approach to longer
mixed-species ion strings. Fast transport of mixed-species ion strings can
significantly reduce the time overhead in certain architectures for scalable
quantum information processing with trapped ions.
