1,097 research outputs found
Glassy Chimeras could be blind to quantum speedup: Designing better benchmarks for quantum annealing machines
Recently, a programmable quantum annealing machine has been built that
minimizes the cost function of hard optimization problems by adiabatically
quenching quantum fluctuations. Tests performed by different research teams
have shown that, indeed, the machine seems to exploit quantum effects. However
experiments on a class of random-bond instances have not yet demonstrated an
advantage over classical optimization algorithms on traditional computer
hardware. Here we present evidence as to why this might be the case. These
engineered quantum annealing machines effectively operate coupled to a
decohering thermal bath. Therefore, we study the finite-temperature critical
behavior of the standard benchmark problem used to assess the computational
capabilities of these complex machines. We simulate both random-bond Ising
models and spin glasses with bimodal and Gaussian disorder on the D-Wave
Chimera topology. Our results show that while the worst-case complexity of
finding a ground state of an Ising spin glass on the Chimera graph is not
polynomial, the finite-temperature phase space is likely rather simple: Spin
glasses on Chimera have only a zero-temperature transition. This means that
benchmarking optimization methods using spin glasses on the Chimera graph might
not be the best benchmark problems to test quantum speedup. We propose
alternative benchmarks by embedding potentially harder problems on the Chimera
topology. Finally, we also study the (reentrant) disorder-temperature phase
diagram of the random-bond Ising model on the Chimera graph and show that a
finite-temperature ferromagnetic phase is stable up to 19.85(15)%
antiferromagnetic bonds. Beyond this threshold the system only displays a
zero-temperature spin-glass phase. Our results therefore show that a careful
design of the hardware architecture and benchmark problems is key when building
quantum annealing machines.Comment: 8 pages, 5 figures, 1 tabl
Domino, an experience of Theatre of the Oppressed
In this moving report the author recounts a series of TO workshops with immigrant mothers in Tehran as the women try to cope with arranged marriages, poverty, sexism, and child-rearing issues. The problems are passed from one generation to the next, but the intervention of TO creates change
Robust Parameter Selection for Parallel Tempering
This paper describes an algorithm for selecting parameter values (e.g.
temperature values) at which to measure equilibrium properties with Parallel
Tempering Monte Carlo simulation. Simple approaches to choosing parameter
values can lead to poor equilibration of the simulation, especially for Ising
spin systems that undergo -order phase transitions. However, starting
from an initial set of parameter values, the careful, iterative respacing of
these values based on results with the previous set of values greatly improves
equilibration. Example spin systems presented here appear in the context of
Quantum Monte Carlo.Comment: Accepted in International Journal of Modern Physics C 2010,
http://www.worldscinet.com/ijmp
Bayesian Optimization for Adaptive MCMC
This paper proposes a new randomized strategy for adaptive MCMC using
Bayesian optimization. This approach applies to non-differentiable objective
functions and trades off exploration and exploitation to reduce the number of
potentially costly objective function evaluations. We demonstrate the strategy
in the complex setting of sampling from constrained, discrete and densely
connected probabilistic graphical models where, for each variation of the
problem, one needs to adjust the parameters of the proposal mechanism
automatically to ensure efficient mixing of the Markov chains.Comment: This paper contains 12 pages and 6 figures. A similar version of this
paper has been submitted to AISTATS 2012 and is currently under revie
SLAVONIC ANTIQUITIES WITH S AND SH/AN UNIVERSAL UNIT OF SACRUM AS AN APPEAL TO COMMON SENSE THROUGH CULTURES
The paper analyses the spiritual and aesthetic messages of the artist Marek Sobczyk whose exposition, containing 15 metal paintings painted over aluminum iron (because it produces sounds and reflects light) with the enigmatic title Slavonic antiquities with S and Sh, represents a powerful stimulus for interdisciplinary studies aimed at active resistance to the global, ideological, and moral crisis of modernity and to discrimination of cultures. The exposition is a unique aesthetic attempt to overcome them
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