Reconfigurable computing for Monte Carlo simulations: results and prospects of the Janus project

Abstract

We describe Janus, a massively parallel FPGA-based computer optimized for the simulation of spin glasses, theoretical models for the behavior of glassy materials. FPGAs (as compared to GPUs or many-core processors) provide a complementary approach to massively parallel computing. In particular, our model problem is formulated in terms of binary variables, and floating-point operations can be (almost) completely avoided. The FPGA architecture allows us to run many independent threads with almost no latencies in memory access, thus updating up to 1024 spins per cycle. We describe Janus in detail and we summarize the physics results obtained in four years of operation of this machine; we discuss two types of physics applications: long simulations on very large systems (which try to mimic and provide understanding about the experimental non-equilibrium dynamics), and low-temperature equilibrium simulations using an artificial parallel tempering dynamics. The time scale of our non-equilibrium simulations spans eleven orders of magnitude (from picoseconds to a tenth of a second). On the other hand, our equilibrium simulations are unprecedented both because of the low temperatures reached and for the large systems that we have brought to equilibrium. A finite-time scaling ansatz emerges from the detailed comparison of the two sets of simulations. Janus has made it possible to perform spin-glass simulations that would take several decades on more conventional architectures. The paper ends with an assessment of the potential of possible future versions of the Janus architecture, based on state-of-the-art technology.

19 pages, 3 figures

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• The three dimensional Ising spin glass in an external magnetic field: the role of the silent majority
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• Dynamical transition in the D = 3 Edwards-Anderson spin glass in an external magnetic field
• Quantum computing for chemistry and physics applications from a Monte Carlo perspective
• Phase Transition in 3d Heisenberg Spin Glasses with Strong Random Anisotropies, through a Multi-GPU Parallelization
• Parallel Tempering Simulation of the three-dimensional Edwards-Anderson Model with Compact Asynchronous Multispin Coding on GPU
• Comment on "Evidence of Non-Mean-Field-Like Low-Temperature Behavior in the Edwards-Anderson Spin-Glass Model"
• Highly optimized simulations on single- and multi-GPU systems of 3D Ising spin glass
• The cumulative overlap distribution function in realistic spin glasses
• Spin-glass dynamics: experiment, theory and simulation
• From quantum-enhanced to quantum-inspired Monte Carlo
• Explicit generation of the branching tree of states in spin glasses
• Numerical study of the overlap Lee-Yang singularities in the three-dimensional Edwards-Anderson model
• Correlated Domains in Spin Glasses