Hybrid scheme for entanglement generation via non-linear excitations

Abstract: Many proposals for realizing quantum devices require the capability of entanglingdistant qubits without moving them. Quantum channels used to this purpose are often made byinteracting quantum systems distributed along one-dimensional lattices, a general setup that havedemonstrated effective, at the expense of a high sensitivity to noise and decoherence, thus requiringgood protection against external interactions. On the other hand, chains of interacting classicalsystems are known to feature dynamical evolutions that make them transmission lines robustagainst noise of various types but, by definition, they cannot convey quantum properties. In thiswork we propose a hybrid scheme, where a semi-classical spin chain, i.e. a chain of interactingparticles with large spin S, is locally coupled with two distant qubits: the idea is that a large valueof S guarantees the presence of robust non-linear excitations (such as dynamical solitons), and yetdoes not totally wipe out the quantum character of the channel, that remains defined as a systemwith a Hilbert space, and whose components are still described by spin operators. The dimension ofthe Hilbert space of one such channel is too large for allowing an exact analysis of the overall(channel+qubits) dynamics; however, using spin-coherent states, we obtain an approximationscheme that allows us to evaluate the amount of entanglement dynamically generated between thetwo distant qubits. We find that when the evolution of the channel is ruled by strongly localizedexcitations, and one has the possibility of switching on and off the coupling between each qubit andthe respective nearby portion of the spin-chain, non-negligible entanglement is indeed generated.We discuss if, and to what extent, this could be a possible way of reducing the vulnerability ofentanglement transfer via quantum channels with respect to noise, imperfections, and decoherence.