Subsystem codes with spatially local generators

We study subsystem codes whose gauge group has local generators in two-dimensional (2D) geometry. It is shown that there exists a family of such codes defined on lattices of size L with the number of logical qubits k and the minimum distance d both proportional to L. The gauge group of these codes involves only two-qubit generators of type XX and ZZ coupling nearest-neighbor qubits (and some auxiliary one-qubit generators). Our proof is not constructive as it relies on a certain version of the Gilbert-Varshamov bound for classical codes. Along the way, we introduce and study properties of generalized Bacon-Shor codes that might be of independent interest. Secondly, we prove that any 2D subsystem n, k, d code with spatially local generators obeys upper bounds kd=O (n) and d^2=O (n). The analogous upper bound proved recently for 2D stabilizer codes is kd^2=O (n). Our results thus demonstrate that subsystem codes can be more powerful than stabilizer codes under the spatial locality constraint.