TY - JOUR T1 - Complexity of the XY antiferromagnet at fixed magnetization JF - Quantum Information and Computation Y1 - 2016 A1 - Andrew M. Childs A1 - David Gosset A1 - Zak Webb AB - 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. VL - 16 U4 - 1-18 UR - http://arxiv.org/abs/1503.07083v1 CP - 1-2 ER -