Topological order

Summary

Topological order is a kind of order in gapped quantum phases at zero temperature that no local order parameter detects. One sign is a ground-state degeneracy that depends on the topology of the surface carrying the system. Another is that no local measurement can tell the ground states apart. It arises in fractional quantum Hall states and in models such as the toric code. Its excitations can be anyons, and its protected degeneracy is a resource for fault-tolerant quantum computation.