2,646 research outputs found
Population annealing: Theory and application in spin glasses
Population annealing is an efficient sequential Monte Carlo algorithm for
simulating equilibrium states of systems with rough free energy landscapes. The
theory of population annealing is presented, and systematic and statistical
errors are discussed. The behavior of the algorithm is studied in the context
of large-scale simulations of the three-dimensional Ising spin glass and the
performance of the algorithm is compared to parallel tempering. It is found
that the two algorithms are similar in efficiency though with different
strengths and weaknesses.Comment: 16 pages, 10 figures, 4 table
Recommended from our members
Population Annealing Monte Carlo Studies of Ising Spin Glasses
Spin glasses are spin-lattice models with quenched disorder and frustration. The mean field long-range Sherrington-Kirkpatrick (SK) model was solved by Parisi and displays replica symmetry breaking (RSB), but the more realistic short-range Edwards-Anderson (EA) model is still not solved. Whether the EA spin glass phase has many pairs of pure states as described by the RSB scenario or a single pair of pure states as described by two-state scenarios such as the droplet/scaling picture is not known yet. Rigorous analytical calculations of the EA model are not available at present and efficient numerical simulations of spin glasses are crucial in making progresses in the field. In addition to being a prototypical example of a classical disordered system with many interesting equilibrium as well as nonequilibrium properties, spin glasses are of great importance across multiple fields from neural networks, various combinatorial optimization problems to benchmark tests of quantum annealing machines. Therefore, it is important to gain a better understanding of the spin glass models.
In an effort to do so, our work has two main parts, one is to develop an efficient algorithm called population annealing Monte Carlo and the other is to explore the physics of spin glasses using thermal boundary conditions. We present a full characterization of the population annealing algorithm focusing on its equilibration properties and make a systematic comparison of population annealing with two well established simulation methods, parallel tempering Monte Carlo and simulated annealing Monte Carlo. We show numerically that population annealing is similar in performance to parallel tempering, each has its own strengths and weaknesses and both algorithms outperform simulated annealing in combinatorial optimization problems.
In thermal boundary conditions, all eight combinations of periodic vs antiperiodic boundary conditions in the three spatial directions appear in the ensemble with their respective Boltzmann weights, thus minimizing finite-size effects due to domain walls. With thermal boundary conditions and sample stiffness extrapolation, we show that our data is consistent with a two-state picture, not the RSB picture for the EA model. Thermal boundary conditions also provides an elegant way to study the phenomena of temperature chaos and bond chaos, and our results are again in agreement with the droplet/scaling scenario
Unconstrained Tree Tensor Network: An adaptive gauge picture for enhanced performance
We introduce a variational algorithm to simulate quantum many-body states
based on a tree tensor network ansatz which releases the isometry constraint
usually imposed by the real-space renormalization coarse-graining: This
additional numerical freedom, combined with the loop-free topology of the tree
network, allows one to maximally exploit the internal gauge invariance of
tensor networks, ultimately leading to a computationally flexible and efficient
algorithm able to treat open and periodic boundary conditions on the same
footing. We benchmark the novel approach against the 1D Ising model in
transverse field with periodic boundary conditions and discuss the strategy to
cope with the broken translational invariance generated by the network
structure. We then perform investigations on a state-of-the-art problem, namely
the bilinear-biquadratic model in the transition between dimer and
ferromagnetic phases. Our results clearly display an exponentially diverging
correlation length and thus support the most recent guesses on the peculiarity
of the transition.Comment: 11 pages, 13 figure
Reentrant Behavior of the Spinodal Curve in a Nonequilibrium Ferromagnet
The metastable behavior of a kinetic Ising--like ferromagnetic model system
in which a generic type of microscopic disorder induces nonequilibrium steady
states is studied by computer simulation and a mean--field approach. We pay
attention, in particular, to the spinodal curve or intrinsic coercive field
that separates the metastable region from the unstable one. We find that, under
strong nonequilibrium conditions, this exhibits reentrant behavior as a
function of temperature. That is, metastability does not happen in this regime
for both low and high temperatures, but instead emerges for intermediate
temperature, as a consequence of the non-linear interplay between thermal and
nonequilibrium fluctuations. We argue that this behavior, which is in contrast
with equilibrium phenomenology and could occur in actual impure specimens,
might be related to the presence of an effective multiplicative noise in the
system.Comment: 7 pages, 4 figures; Final version to appear in Phys. Rev. E; Section
V has been revise
Scalable Emulation of Sign-ProblemFree Hamiltonians with Room Temperature p-bits
The growing field of quantum computing is based on the concept of a q-bit
which is a delicate superposition of 0 and 1, requiring cryogenic temperatures
for its physical realization along with challenging coherent coupling
techniques for entangling them. By contrast, a probabilistic bit or a p-bit is
a robust classical entity that fluctuates between 0 and 1, and can be
implemented at room temperature using present-day technology. Here, we show
that a probabilistic coprocessor built out of room temperature p-bits can be
used to accelerate simulations of a special class of quantum many-body systems
that are sign-problemfree or stoquastic, leveraging the well-known
Suzuki-Trotter decomposition that maps a -dimensional quantum many body
Hamiltonian to a +1-dimensional classical Hamiltonian. This mapping allows
an efficient emulation of a quantum system by classical computers and is
commonly used in software to perform Quantum Monte Carlo (QMC) algorithms. By
contrast, we show that a compact, embedded MTJ-based coprocessor can serve as a
highly efficient hardware-accelerator for such QMC algorithms providing several
orders of magnitude improvement in speed compared to optimized CPU
implementations. Using realistic device-level SPICE simulations we demonstrate
that the correct quantum correlations can be obtained using a classical
p-circuit built with existing technology and operating at room temperature. The
proposed coprocessor can serve as a tool to study stoquastic quantum many-body
systems, overcoming challenges associated with physical quantum annealers.Comment: Fixed minor typos and expanded Appendi
Monte-Carlo simulation of supercooled liquids using a self-consistent local temperature
We combine Creutz energy conservation with Kawasaki spin exchange to simulate
the microcanonical dynamics of a system of interacting particles. Relaxation
occurs via Glauber spin-flip activation using a self-consistent temperature.
Heterogeneity in the dynamics comes from finite-size constraints on the spin
exchange that yield a distribution of correlated regions. The simulation
produces a high-frequency response that can be identified with the boson peak,
and a lower-frequency peak that contains non-Debye relaxation and non-Arrhenius
activation, similar to the primary response of supercooled liquids.Comment: 16 pages, 4 figure
GPU accelerated population annealing algorithm
Population annealing is a promising recent approach for Monte Carlo
simulations in statistical physics, in particular for the simulation of systems
with complex free-energy landscapes. It is a hybrid method, combining
importance sampling through Markov chains with elements of sequential Monte
Carlo in the form of population control. While it appears to provide
algorithmic capabilities for the simulation of such systems that are roughly
comparable to those of more established approaches such as parallel tempering,
it is intrinsically much more suitable for massively parallel computing. Here,
we tap into this structural advantage and present a highly optimized
implementation of the population annealing algorithm on GPUs that promises
speed-ups of several orders of magnitude as compared to a serial implementation
on CPUs. While the sample code is for simulations of the 2D ferromagnetic Ising
model, it should be easily adapted for simulations of other spin models,
including disordered systems. Our code includes implementations of some
advanced algorithmic features that have only recently been suggested, namely
the automatic adaptation of temperature steps and a multi-histogram analysis of
the data at different temperatures.Comment: 12 pages, 3 figures and 5 tables, code at
https://github.com/LevBarash/PAisin
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