Barbara M. Terhal, Guido Burkard
Physical Review A - AMO
We describe a classical approximation algorithm for evaluating the ground state energy of the classical Ising Hamiltonian with linear terms on an arbitrary planar graph. The running time of the algorithm grows linearly with the number of spins and exponentially with 1/ε, where ε is the worst-case relative error. This result contrasts the well known fact that exact computation of the ground state energy for the two-dimensional Ising spin glass model is NP-hard. We also present a classical approximation algorithm for the quantum Local Hamiltonian Problem or Quantum Ising Spin Glass problem on a planar graph with bounded degree which is known to be a QMA-complete problem. Using a different technique we find a classical approximation algorithm for the quantum Ising spin glass problem on the simplest planar graph with unbounded degree, the star graph.
Barbara M. Terhal, Guido Burkard
Physical Review A - AMO
David P. DiVincenzo, Patrick Hayden, et al.
Foundations of Physics
Nikhil Bansal, Kirk Pruhs
FOCS 2010
Barbara M. Terhal, Micha Horodecki, et al.
Journal of Mathematical Physics