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 (pseudopure) 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.