9,666 research outputs found
Quantum Belief Propagation
We present an accurate numerical algorithm, called quantum belief propagation
(QBP), for simulation of one-dimensional quantum systems at non-zero
temperature. The algorithm exploits the fact that quantum effects are
short-range in these systems at non-zero temperature, decaying on a length
scale inversely proportional to the temperature. We compare to exact results on
a spin-1/2 Heisenberg chain. Even a very modest calculation, requiring
diagonalizing only 10-by-10 matrices, reproduces the peak susceptibility with a
relative error of less than , while more elaborate calculations
further reduce the error.Comment: 4 pages, 1 figure; revised time estimates due to improved
implementation. Typographical corrections to Eq. 7 made; thanks to David
Poulin for pointing out the mistak
Decay of Correlations in Fermi Systems at Non-zero Temperature
The locality of correlation functions is considered for Fermi systems at
non-zero temperature. We show that for all short-range, lattice Hamiltonians,
the correlation function of any two fermionic operators decays exponentially
with a correlation length which is of order the inverse temperature for small
temperature. We discuss applications to numerical simulation of quantum systems
at non-zero temperature.Comment: 3 pages, 0 figure
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