Trapped-ion quantum simulation of tunable-range Heisenberg chains
  Quantum-optical techniques allow for generating controllable spin-spin interactions between ions, making trapped ions an ideal quantum simulator of Heisenberg chains. A single parameter, the detuning of the Raman coupling, allows to switch between ferromagnetic and antiferromagnetic chains, and to modify the range of the interactions. On the antiferromagnetic side, the system can be tuned from an extreme long-range limit, in which any pair of ions interacts with almost equal strength, to interactions with a $1/r^3$ decay. By exact diagonalization, we study how a system of up to 20 ions behaves upon tuning the interactions. We find that it undergoes a transition from a dimerized state with extremely short-ranged correlations towards a state with quasi long-range order, that is, algebraically decaying correlations. On the ferromagnetic side of the system, we demonstrate the feasibility of witnessing non-locality of quantum correlations. 
Tobias Gra{\ss} and Maciej Lewenstein
cond-mat.quant-gas cond-mat.str-el quant-ph