In 1997 Alexei Kitaev, at Caltech, presents "Fault-tolerant quantum computation by anyons" (published 2003), introducing the toric code: the first quantum error-correction scheme based on topological properties. Kitaev encodes a logical qubit in the collective state of many physical qubits arranged on a toroidal surface, so local errors do not destroy the globally protected information; anyons signal errors via their topological behavior. The toric code is the theoretical basis of all modern fault-tolerant quantum computing architectures, including Google's, IBM's, and Microsoft's.