Perfect transfer of multiple excitations in quantum networks
  We present a general formalism to the problem of perfect state-transfer (PST), where the state involves multiple excitations of the quantum network. A key feature of our formalism is that it allows for inclusion of nontrivial interactions between the excitations. Hence, it is perfectly suited to addressing the problem of PST in the context of various types of physical realizations. The general formalism is also flexible enough to account for situations where multiple excitations are "focused" onto the same site. 
T. Brougham, G. M. Nikolopoulos, and I. Jex
quant-ph