N. Y. Yao1†∗, A. V. Gorshkov2†, C. R. Laumann1,3†, A. M. Lauchli, J. Ye, M. D. Lukin Physics Department, Harvard University, Cambridge, MA 02138, U.S.A. Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA 91125, U.S.A. ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, U.S.A. Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, Colorado 80309, USA †These authors contributed equally to this work and ∗e-mail: nyao@fas.harvard.edu