FPGA-Based Prototype of a Quantum Annealing Simulator for Sparse Ising Model

Quantum annealing (QA) is a probabilistic approx-imation method to find the global optimum of a combinatorial optimization problem. QA is done on quantum annealers such as D-wave using quantum properties. Since the number of qubits in quantum annealers is limited, it is difficult to use those to solve large-scale real-world problems. Therefore, quantum annealing simulation on digital computers is necessary. In this paper, we discuss an FPGA based quantum annealing simulator for sparse Ising model. Unlike a fully-connected Ising model, the number of connections among spins in sparse model is limited. Highly sparse Ising models require significantly low amount of computations while allowing more parallel operations. One the other hand, sparsity and the connections among spins are not the same for different Ising models, and it is difficult to propose one specific accelerator architecture for all. We propose a method to automatically generate an application specific accelerator archi-tecture for a given sparse Ising model. The proposed accelerator fully exploits the parallelism to increase the processing speed. We design an FPGA prototype of the proposed accelerator and confirmed the correct behavior. In future, we expect to extend the proposed method to execute large quantum annealing simulations using multiple FPGAs.