We thank A. Chandran, E. Demler, A. Polkovnikov and A. Vishwanath for discussions. This work was supported by the National Science Foundation (NSF), CUA, ARO, AFOSR MURI, DOE and a Vannevar Bush Faculty Fellowship. A.O. acknowledges support from a research fellowship from the German Research Foundation (DFG). H.L. acknowledges support from a National Defense Science and Engineering Graduate (NDSEG) fellowship. S. Schwartz acknowledges funding from the European Union under the Marie Skłodowska Curie Individual Fellowship Programme H2020-MSCA-IF-2014 (project number 658253). H.P. acknowledges support from the NSF through a grant at the Institute of Theoretical Atomic Molecular and Optical Physics (ITAMP) at Harvard University and the Smithsonian Astrophysical Observatory. M.E. acknowledges funding provided by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center (NSF grant PHY-1733907). S. Sachdev acknowledges support from the US Department of Energy (grant number DE-SC0019030).

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Nature thanks David A. Huse and the other anonymous reviewer(s) for their contribution to the peer review of this work.