Reweighted Time-Evolving Block Decimation for Improved Quantum Dynamics Simulations

TL;DR

The paper proposes a reweighted TEBD algorithm that improves quantum dynamics simulations by prioritizing low-weight expectation values, leading to higher accuracy and better conservation of quantities.

Contribution

It introduces a reweighted TEBD method that enhances the accuracy of MPDO simulations by focusing on important low-weight expectation values during truncation.

Findings

rTEBD outperforms standard TEBD in accuracy for MPDO simulations.

rTEBD better preserves conserved quantities during evolution.

The method is sometimes superior to TEBD using MPS.

Abstract

We introduce a simple yet significant improvement to the time-evolving block decimation (TEBD) tensor network algorithm for simulating the time dynamics of strongly correlated one-dimensional (1D) mixed quantum states. The efficiency of 1D tensor network methods stems from using a product of matrices to express either: the coefficients of a wavefunction, yielding a matrix product state (MPS); or the expectation values of a density matrix, yielding a matrix product density operator (MPDO). To avoid exponential computational costs, TEBD truncates the matrix dimension while simulating the time evolution. However, when truncating an MPDO, TEBD does not favor the likely more important low-weight expectation values, such as $\langle c_i^\dagger c_j \rangle$, over the exponentially many high-weight expectation values, such as $\langle c_{i_1}^\dagger c^\dagger_{i_2} \cdots c_{i_n} \rangle$ of weight $n$, despite the critical importance of the low-weight expectation values. Motivated by this shortcoming, we propose a reweighted TEBD (rTEBD) algorithm that deprioritizes high-weight expectation values by a factor of $\gamma^{-n}$ during the truncation. This modification makes rTEBD significantly more accurate than the TEBD time-dependent simulation of an MPDO, and competitive with and sometimes better than TEBD using MPS. Furthermore, by prioritizing low-weight expectation values, rTEBD preserves conserved quantities to high precision.