Looped Pipelines Enabling Effective 3D Qubit Lattices in a Strictly 2D Device

TL;DR

The paper introduces looped pipelines that enable 3D-like qubit lattice advantages in strictly 2D quantum devices, leveraging qubit shuttling to enhance error mitigation and fault-tolerant quantum computing.

Contribution

It proposes a novel looped pipeline architecture that stacks qubit arrays in 2D devices, broadening the scope of quantum error correction and reducing resource costs.

Findings

Enables layered 2D codes with transversal CNOTs

Reduces magic state distillation costs by two orders of magnitude

Maintains code thresholds with realistic noise models

Abstract

Many quantum computing platforms are based on a two-dimensional physical layout. Here we explore a concept called looped pipelines which permits one to obtain many of the advantages of a 3D lattice while operating a strictly 2D device. The concept leverages qubit shuttling, a well-established feature in platforms like semiconductor spin qubits and trapped-ion qubits. The looped pipeline architecture has similar hardware requirements to other shuttling approaches, but can process a stack of qubit arrays instead of just one. Even a stack of limited height is enabling for diverse schemes ranging from NISQ-era error mitigation through to fault-tolerant codes. For the former, protocols involving multiple states can be implemented with a space-time resource cost comparable to preparing one noisy copy. For the latter, one can realise a far broader variety of code structures; as an example we consider layered 2D codes within which transversal CNOTs are available. Under reasonable assumptions this approach can reduce the space-time cost of magic state distillation by two orders of magnitude. Numerical modelling using experimentally-motivated noise models verifies that the architecture provides this benefit without significant reduction to the code's threshold.