%0 Journal Article %J Quantum Information and Computation %D 2016 %T Complexity of the XY antiferromagnet at fixed magnetization %A Andrew M. Childs %A David Gosset %A Zak Webb %X We prove that approximating the ground energy of the antiferromagnetic XY model on a simple graph at fixed magnetization (given as part of the instance specification) is QMA-complete. To show this, we strengthen a previous result by establishing QMA-completeness for approximating the ground energy of the Bose-Hubbard model on simple graphs. Using a connection between the XY and Bose-Hubbard models that we exploited in previous work, this establishes QMA-completeness of the XY model. %B Quantum Information and Computation %V 16 %P 1-18 %8 2016/01/01 %G eng %U http://arxiv.org/abs/1503.07083v1 %N 1-2