@article{Cubitt2015UndecidabilityOT,
title={Undecidability of the spectral gap},
author={T. S. Cubitt and D. P{\'e}rez-Garc{\'i}a and M. Wolf},
journal={Nature},
year={2015},
volume={528},
pages={207-211}
}

The spectral gap—the energy difference between the ground state and first excited state of a system—is central to quantum many-body physics. Many challenging open problems, such as the Haldane conjecture, the question of the existence of gapped topological spin liquid phases, and the Yang–Mills gap conjecture, concern spectral gaps. These and other problems are particular cases of the general spectral gap problem: given the Hamiltonian of a quantum many-body system, is it gapped or gapless… Expand