A topological state of matter governed by a kind of -gauge theory and thought to exhibit topological order. The state was originally conceived under the name resonating valence bond states in: 8 2 (1973) 153-160 [doi:10.1016/0025-5408(73)90167-0] Further early discussion: Textbook account: Further review: Lucile Savary, Leon Balents, Quantum Spin Liquids, Rep. Prog. Phys. 80 016502 (2017) [arXiv:1601.03742, doi:10.1088/0034-4885/80/1/016502] C. Broholm et al.: Quantum spin liquids, Science 367..