3 years ago

# Precise extrapolation of the correlation function asymptotics in uniform tensor network states with application to the Bose-Hubbard and XXZ models.

Piotr Czarnik, Marek M. Rams, Lukasz Cincio

We analyze the problem of extracting the correlation length from infinite matrix product states (MPS) and corner transfer matrix (CTM) simulations. When the correlation length is calculated directly from the transfer matrix, it is typically significantly underestimated for finite bond dimensions used in numerical simulation. This is true even when one considers ground states at a distance from the critical point. In this article we introduce extrapolation procedure to overcome this problem. To that end we quantify how much the dominant part of the MPS/CTM transfer matrix spectrum deviates from being continuous. The latter is necessary to capture the exact asymptotics of the correlation function where the exponential decay is typically modified by an additional algebraic term. By extrapolating such a refinement parameter to zero, we show that we are able to recover the exact value of the correlation length with high accuracy. In a generic setting, our method reduces the error by a factor of $\sim 100$ as compared to the results obtained without extrapolation and a factor of $\sim 10$ as compared to simple extrapolation schemes employing bond dimension. We test our approach in a number of solvable models both in 1d and 2d. Subsequently, we apply it to one-dimensional XXZ spin-$\frac{3}{2}$ and the Bose-Hubbard models in a massive regime in the vicinity of Berezinskii-Kosterlitz-Thouless critical point. We then fit the scaling form of the correlation length and extract the position of the critical point and obtain results comparable or better than those of other state-of-the-art numerical methods. Finally, we show how the algebraic part of the correlation function asymptotics can be directly recovered from the scaling of the dominant form factor within our approach.

Publisher URL: http://arxiv.org/abs/1801.08554

DOI: arXiv:1801.08554v1

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