Optimal state transfer and entanglement generation in power-law interacting systems

We present an optimal protocol for encoding an unknown qubit state into a multiqubit Greenberger-Horne-Zeilinger-like state and, consequently, transferring quantum information in large systems exhibiting power-law (1/r^\alpha interactions. For all power-law exponents \alphabetween dand 2d+1 where dis the dimension of the system, the protocol yields a polynomial speedup for \alpha>2dand a superpolynomial speedup for $\alpha\leq...