  Frustration represents an essential feature in the behavior of magnetic
materials when constraints on the microscopic Hamiltonian cannot be satisfied
simultaneously. This gives rise to exotic phases of matter including spin
liquids, spin ices, and stripe phases. Here we demonstrate an approach to
understanding the microscopic effects of frustration by computing the phases of
a 468-spin Shastry-Sutherland Ising Hamiltonian using a quantum annealer. Our
approach uses mean-field boundary conditions to mitigate effects of finite size
and defects alongside an iterative quantum annealing protocol to simulate
statistical physics. We recover all phases of the Shastry-Sutherland Ising
model -- including the well-known fractional magnetization plateau -- and the
static structure factor characterizing the critical behavior at these
transitions. These results establish quantum annealing as an emerging method in
understanding the effects of frustration on the emergence of novel phases of
matter and pave the way for future comparisons with real experiments.
