Infinite boundary conditions for matrix product state calculations

TL;DR

This paper introduces a formalism using infinite boundary conditions in matrix product state calculations to accurately study the dynamics of quantum many-body systems in the thermodynamic limit, avoiding finite-size effects.

Contribution

The authors develop a novel approach with infinite boundary conditions for matrix product states, improving accuracy and efficiency over traditional finite-size methods.

Findings

Efficient calculation of spectral functions in infinite systems

Elimination of boundary effects like Friedel oscillations

Enhanced accuracy in dynamical simulations

Abstract

We propose a formalism to study dynamical properties of a quantum many-body system in the thermodynamic limit by studying a finite system with infinite boundary conditions (IBC) where both finite size effects and boundary effects have been eliminated. For one-dimensional systems, infinite boundary conditions are obtained by attaching two boundary sites to a finite system, where each of these two sites effectively represents a semi-infinite extension of the system. One can then use standard finite-size matrix product state techniques to study a region of the system while avoiding many of the complications normally associated with finite-size calculations such as boundary Friedel oscillations. We illustrate the technique with an example of time evolution of a local perturbation applied to an infinite (translationally invariant) ground state, and use this to calculate the spectral function of the S=1 Heisenberg spin chain. This approach is more efficient and more accurate than conventional simulations based on finite-size matrix product state and density-matrix renormalization-group approaches.