Inplace Access to the Surface Code Y Basis

TL;DR

This paper introduces a method to significantly reduce the cost of Y basis measurement and initialization in the surface code, enabling more efficient quantum error correction and measurement on hardware with limited space.

Contribution

It proposes a novel technique using diagonally fused twist defects to perform Y basis operations without reducing code distance or leaving the patch boundary.

Findings

Nearly an order of magnitude reduction in Y basis measurement cost

Benchmarking shows improved performance under circuit noise

Enables Pauli measurement tomography on space-limited hardware

Abstract

In this paper, I cut the cost of Y basis measurement and initialization in the surface code by nearly an order of magnitude. Fusing twist defects diagonally across the surface code patch reaches the Y basis in $\lfloor d/2 \rfloor + 2$ rounds, without leaving the bounding box of the patch and without reducing the code distance. I use Monte Carlo sampling to benchmark the performance of the construction under circuit noise, and to analyze the distribution of logical errors. Cheap inplace Y basis measurement reduces the cost of S gates and magic state factories, and unlocks Pauli measurement tomography of surface code qubits on space-limited hardware.