Hybrid scheme for entanglement generation via non-linear excitations

Abstract: Many proposals for realizing quantum devices require the capability of entangling distant qubits without moving them. Quantum channels used to this purpose are often made by interacting quantum systems distributed along one-dimensional lattices, a general setup that have demonstrated effective, at the expense of a high sensitivity to noise and decoherence, thus requiring good protection against external interactions. On the other hand, chains of interacting classical systems are known to feature dynamical evolutions that make them transmission lines robust against noise of various types but, by definition, they cannot convey quantum properties. In this work we propose a hybrid scheme, where a semi-classical spin chain, i.e. a chain of interacting particles with large spin S, is locally coupled with two distant qubits: the idea is that a large value of S guarantees the presence of robust non-linear excitations (such as dynamical solitons), and yet does not totally wipe out the quantum character of the channel, that remains defined as a system with a Hilbert space, and whose components are still described by spin operators. The dimension of the 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 approximation scheme that allows us to evaluate the amount of entanglement dynamically generated between the two distant qubits. We find that when the evolution of the channel is ruled by strongly localized excitations, and one has the possibility of switching on and off the coupling between each qubit and the 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 of entanglement transfer via quantum channels with respect to noise, imperfections, and decoherence.