An Ising Computer Based on Simulated Quantum Annealing by Path Integral Monte Carlo Method

In the near future, one of the main processes is solving large combinatorial optimization problems. However, the performance growth of von Neumann architecture will slow due to the end of semiconductor scaling. To resolve this problem, we propose an Ising computer that maps the optimization problems to the ground state search of Ising models. We previously proposed a computer that finds the ground state of Ising models by simulated annealing (SA) approximately. Though the solution quality of the previous prototype is comparable to that of SA, enhancing the solution quality will be required to solve real-world applications. In this paper, we present our FPGA-based Ising computer that executes simulated quantum annealing by using a path integral quantum Monte Carlo method for Ising models on a 48-by-48 king graph with 8-bit couplings. We also propose a shared random number supply, which contributes to decrease the number of random number generators to two. Experimental results indicate that the proposed Ising computer is more than 15 times faster to obtain 99.9%-solution with a probability of 99% than SA running on a state-of-the-art CPU.