Preparing Valence-Bond-Solid states on noisy intermediate-scale quantum computers

TL;DR

This paper introduces a non-deterministic method for preparing Valence-Bond-Solid states on noisy intermediate-scale quantum computers, enabling efficient exploration of quantum spin models beyond traditional numerical techniques.

Contribution

It presents a shallow, optimized quantum circuit approach for VBS state preparation that overcomes depth limitations of tensor-network methods on NISQ devices.

Findings

Shallow circuits of depth independent of lattice size are derived.

Optimization schemes outperform standard basis gate decomposition.

Quadratic reduction in repetition overhead for bipartite lattice VBS states.

Abstract

Quantum state preparation is a key step in all digital quantum simulation algorithms. Here we propose methods to initialize on a gate-based quantum computer a general class of quantum spin wave functions, the so-called Valence-Bond-Solid (VBS) states, that are important for two reasons. First, VBS states are the exact ground states of a class of interacting quantum spin models introduced by Affleck, Kennedy, Lieb and Tasaki (AKLT). Second, the two-dimensional VBS states are universal resource states for measurement-based quantum computing. We find that schemes to prepare VBS states based on their tensor-network representations yield quantum circuits that are too deep to be within reach of noisy intermediate-scale quantum (NISQ) computers. We then apply the general non-deterministic method herein proposed to the preparation of the spin-1 and spin-3/2 VBS states, the ground states of the AKLT models defined in one dimension and in the honeycomb lattice, respectively. Shallow quantum circuits of depth independent of the lattice size are explicitly derived for both cases, making use of optimization schemes that outperform standard basis gate decomposition methods. Given the probabilistic nature of the proposed routine, two strategies that achieve a quadratic reduction of the repetition overhead for any VBS state defined on a bipartite lattice are devised. Our approach should permit to use NISQ processors to explore the AKLT model and variants thereof, outperforming conventional numerical methods in the near future.