IQI Weekly Seminar

Abstract: Covariant codes are quantum codes such that symmetry transformations on the logical system could be realized by symmetry transformations on the physical system, usually with limited capability of performing quantum error correction (an important case being the Eastin-Knill theorem). The need for understanding the limits of covariant quantum error correction arises in various realms of physics including fault-tolerant quantum computation, condensed matter physics and quantum gravity. Here, we explore covariant quantum error correction from the perspectives of quantum metrology and quantum resource theory, building solid connections between these formerly disparate fields. We prove new and powerful lower bounds on the infidelity of covariant quantum error correction, which not only extend the scope of previous no-go results but also provide a substantial improvement over existing bounds. Explicit lower bounds are derived for both erasure and depolarizing noises. We also present a type of covariant codes which nearly saturate these lower bounds.