# Spatial Noise Correlations in a Si/SiGe Two-Qubit Device from Bell State Coherences

## TL;DR

This study investigates spatial noise correlations in a Si/SiGe two-qubit device using Bell state coherence measurements, revealing weak low-frequency correlations and no high-frequency correlations, informing quantum error correction strategies.

## Contribution

The paper introduces a method using decoherence-free subspaces to measure noise correlations in a silicon-based two-qubit device, providing new insights into noise behavior relevant for quantum error correction.

## Key findings

- Weak correlations in low-frequency noise
- No detectable correlations in high-frequency noise
- Theoretical model explains additive effects of noise sources

## Abstract

We study spatial noise correlations in a Si/SiGe two-qubit device with integrated micromagnets. Our method relies on the concept of decoherence-free subspaces, whereby we measure the coherence time for two different Bell states, designed to be sensitive only to either correlated or anti-correlated noise respectively. From these measurements, we find weak correlations in low-frequency noise acting on the two qubits, while no correlations could be detected in high-frequency noise. A theoretical model and numerical simulations give further insight into the additive effect of multiple independent (anti-)correlated noise sources with an asymmetric effect on the two qubits. Such a scenario is plausible given the data and our understanding of the physics of this system. This work is highly relevant for the design of optimized quantum error correction codes for spin qubits in quantum dot arrays, as well as for optimizing the design of future quantum dot arrays.