Non-stabilizerness versus entanglement in matrix product states

TL;DR

This paper explores the relationship between entanglement and non-stabilizerness (magic) in matrix product states, revealing that magic converges faster than entanglement with respect to bond dimension, especially at critical points.

Contribution

It demonstrates that non-stabilizerness converges more rapidly than entanglement in MPS and introduces improved methods for computing mutual magic and information.

Findings

Magic converges with bond dimension faster than entanglement.

At critical points, full state magic shows $1/ ext{chi}^2$ convergence.

Mutual magic scales slower than mutual information with partition size.

Abstract

In this paper, we investigate the relationship between entanglement and non-stabilizerness (also known as magic) in matrix product states (MPSs). We study the relation between magic and the bond dimension used to approximate the ground state of a many-body system in two different contexts: full state of magic and mutual magic (the non-stabilizer analogue of mutual information, thus free of boundary effects) of spin-1 anisotropic Heisenberg chains. Our results indicate that obtaining converged results for non-stabilizerness is typically considerably easier than entanglement. For full state magic at critical points and at sufficiently large volumes, we observe convergence with $1/\chi^2$, with $\chi$ being the MPS bond dimension. At small volumes, magic saturation is so quick that, within error bars, we cannot appreciate any finite-$\chi$ correction. Mutual magic also shows a fast convergence with bond dimension, whose specific functional form is however hindered by sampling errors. As a by-product of our study, we show how Pauli-Markov chains (originally formulated to evaluate magic) resets the state of the art in terms of computing mutual information for MPS. We illustrate this last fact by verifying the logarithmic increase of mutual information between connected partitions at critical points. By comparing mutual information and mutual magic, we observe that, for connected partitions, the latter is typically scaling much slower - if at all - with the partition size, while for disconnected partitions, both are constant in size.