Southwest Quantum Information and Technology

Coherence in logical quantum channels

Presenting Author: Joseph Iverson, California Institute of Technology
Contributing Author(s): John Preskill

We study the effectiveness of quantum error correction against coherent noise. Coherent noise can cause the infidelity to accumulate quadratically when a fixed channel is applied many times in succession, rather than linearly as in the case of incoherent noise. We consider stabilizer quantum codes, and describe how to characterize coherence of the residual logical noise after applying coherent physical noise followed by error recovery. For the case of the toric code subjected to independent coherent noise, and for minimal weight decoding, we prove that the logical channel becomes incoherent as the size of the code increases, assuming that the physical noise strength is below a specified constant. A similar conclusion holds for weakly correlated coherent noise. We also comment on extensions of these results to other codes and other decoders. Our work provides evidence indicating that fault-tolerant quantum computing schemes will work effectively against coherent noise.

(Session 5 : Sunday from 5:00pm - 7:00pm)