Fault-tolerant quantum computation against biased noise

TL;DR

This paper presents a fault-tolerant quantum computing scheme optimized for highly biased noise environments, significantly improving error thresholds by exploiting noise asymmetry, especially in dephasing-dominated scenarios.

Contribution

The authors develop a fault-tolerance scheme tailored for biased noise, demonstrating improved accuracy thresholds by leveraging noise asymmetry in quantum operations.

Findings

Thresholds are higher with noise bias, e.g., fivefold increase with four orders of magnitude bias.

Scheme uses only preparations, measurements, and CPHASE gates, simplifying implementation.

Rigorous bounds on error thresholds are established for biased noise conditions.

Abstract

We formulate a scheme for fault-tolerant quantum computation that works effectively against highly biased noise, where dephasing is far stronger than all other types of noise. In our scheme, the fundamental operations performed by the quantum computer are single-qubit preparations, single-qubit measurements, and conditional-phase (CPHASE) gates, where the noise in the CPHASE gates is biased. We show that the accuracy threshold for quantum computation can be improved by exploiting this noise asymmetry; e.g., if dephasing dominates all other types of noise in the CPHASE gates by four orders of magnitude, we find a rigorous lower bound on the accuracy threshold higher by a factor of five than for the case of unbiased noise.