The infinite occupation number basis of bosons - solving a numerical challenge

TL;DR

This paper introduces a new truncation scheme for bosonic lattice systems that includes a coherent-tail state, improving numerical accuracy and efficiency in representing the many-body ground state.

Contribution

The authors propose a novel truncation method adding a coherent-tail state to the local occupation basis, enhancing numerical methods for bosonic systems.

Findings

Improved numerical accuracy in ground state calculations.

Enhanced efficiency of the Gutzwiller and dynamical mean-field methods.

Better representation of condensate contributions.

Abstract

In any bosonic lattice system, which is not dominated by local interactions and thus "frozen" in a Mott-type state, numerical methods have to cope with the infinite size of the corresponding Hilbert space even for finite lattice sizes. While it is common practice to restrict the local occupation number basis to $N_c$ lowest occupied states, the presence of a finite condensate fraction requires the complete number basis for an exact representation of the many-body ground state. In this work we present a novel truncation scheme to account for contributions from higher number states. By simply adding a single \textit{coherent-tail} state to this common truncation, we demonstrate increased numerical accuracy and the possible increase in numerical efficiency of this method for the Gutzwiller variational wave function and within dynamical mean-field theory.