# A high threshold code for modular hardware with asymmetric noise

## TL;DR

This paper proposes a fault-tolerant quantum computing approach using a simple error detecting code combined with a surface code, achieving high error thresholds under asymmetric noise conditions.

## Contribution

It introduces a novel fault-tolerant quantum computing scheme with a customized decoder and demonstrates superior error thresholds compared to standard surface codes under asymmetric noise.

## Key findings

- Threshold gate-level error rate of 1.42% with asymmetric noise
- Threshold increases to 6.24% with higher local operation fidelity
- Method outperforms standard surface code under specified noise conditions

## Abstract

We consider an approach to fault tolerant quantum computing based on a simple error detecting code operating as the substrate for a conventional surface code. We develop a customised decoder to process the information about the likely location of errors, obtained from the error detect stage, with an advanced variant of the minimum weight perfect matching algorithm. A threshold gate-level error rate of 1.42% is found for the concatenated code given highly asymmetric noise. This is superior to the standard surface code and remains so as we introduce a significant component of depolarising noise; specifically, until the latter is 70% the strength of the former. Moreover, given the asymmetric noise case, the threshold rises to 6.24% if we additionally assume that local operations have 20 times higher fidelity than long range gates. Thus for systems that are both modular and prone to asymmetric noise our code structure can be very advantageous.