New perspectives on covariant quantum error correction

TL;DR

This paper investigates the fundamental limits of covariant quantum error correction under continuous symmetries, establishing new bounds and connecting quantum metrology and resource theory.

Contribution

It introduces new lower bounds on infidelity for covariant codes, extending previous no-go results and providing nearly optimal code constructions.

Findings

Derived explicit lower bounds for erasure and depolarizing noise.

Connected covariant error correction with quantum metrology and resource theory.

Presented covariant codes that nearly saturate the bounds.

Abstract

Covariant codes are quantum codes such that a symmetry transformation on the logical system could be realized by a symmetry transformation 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 with respect to continuous symmetries from the perspectives of quantum metrology and quantum resource theory, establishing 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 saturates these lower bounds.