Optimization and Decoding QEC

Geometrically local quantum codes, which are error-correcting codes embedded in R^D with the checks only acting on qubits within a fixed spatial distance, have garnered significant interest. Recently, it has been demonstrated how to achieve geometrically local codes that maximize both the dimension and the distance, as well as the energy barrier of the code. In this work, we focus on the constructions involving subdivision and show that they have an almost linear time decoder, obtained by combining the decoder of the outer good qLDPC code and a generalized version of the Union-Find decoder. This provides the first decoder for an optimal 3D geometrically local code. We also consider the decoder under random circuit level noise and demonstrate the existence of a finite threshold error rate.