Abstract
We consider a computational problem where the goal is to approximate the maximum eigenvalue of a twolocal Hamiltonian that describes Heisenberg interactions between qubits located at the vertices of a graph. Previous work has shed light on this problemâ€™s approximability by product states. For any instance of this problem the maximum energy attained by a product state is lower bounded by the Max Cut of the graph and upper bounded by the standard GoemansWilliamson semidefinite programming relaxation of it. Gharibian and Parekh described an efficient classical approximation algorithm for this problem which outputs a product state with energy at least 0.498 times the maximum eigenvalue in the worst case, and observe that there exist instances where the best product state has energy 1/2 of optimal. We investigate approximation algorithms with performance exceeding this limitation which are based on optimizing over tensor products of fewqubit states and shallow quantum circuits. We provide an efficient classical algorithm which achieves an approximation ratio of at least 0.53 in the worst case. We also show that for any instance defined by a 3 or 4regular graph, there is an efficiently computable shallow quantum circuit that prepares a state with energy larger than the best product state (larger even than its semidefinite programming relaxation).
BibTeX  Entry
@InProceedings{anshu_et_al:LIPIcs:2020:12066,
author = {Anurag Anshu and David Gosset and Karen Morenz},
title = {{Beyond Product State Approximations for a Quantum Analogue of Max Cut}},
booktitle = {15th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2020)},
pages = {7:17:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {9783959771467},
ISSN = {18688969},
year = {2020},
volume = {158},
editor = {Steven T. Flammia},
publisher = {Schloss DagstuhlLeibnizZentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/opus/volltexte/2020/12066},
URN = {urn:nbn:de:0030drops120660},
doi = {10.4230/LIPIcs.TQC.2020.7},
annote = {Keywords: Approximation algorithms, Quantum manybody systems}
}
Keywords: 

Approximation algorithms, Quantum manybody systems 
Collection: 

15th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2020) 
Issue Date: 

2020 
Date of publication: 

08.06.2020 