Quantum Phase Transition of Ground-state Entanglement in a Heisenberg   Spin Chain Simulated in an NMR Quantum Computer
  Using an NMR quantum computer, we experimentally simulate the quantum phase transition of a Heisenberg spin chain. The Hamiltonian is generated by a multiple pulse sequence, the nuclear spin system is prepared in its (pseudo-pure) ground state and the effective Hamiltonian varied in such a way that the Heisenberg chain is taken from a product state to an entangled state and finally to a different product state. 
Xinhua Peng, Jiangfeng Du, Dieter Suter