Improving Phase Coherence in Flux Tunable Qubit Lattices

Tunable coupler-based lattice architectures are a promising modality in superconducting quantum computing [1]. However, these systems are highly susceptible to both intrinsic and extrinsic flux noise, making it challenging to maintain coherence while balancing control and heat load requirements. While academic discussions often focus on intrinsic flux noise, the origins and mitigations of extrinsic flux noise from control hardware are less often discussed, or solutions used do not adequately address the needs of scaled qubit systems. This talk will delve into practical techniques for characterizing and mitigating extrinsic flux noise caused by current noise originating from control hardware and associated power systems. We validate bench-top noise measurements using various qubit-informed noise metrology techniques [2,3] and demonstrate significant improvements in free-induction decay time ($T_2^*$) and echo decay time ($T_{2E}$) both on and off the flux sweet spot through a straightforward mitigation strategy. We will also discuss how this solution does not fully resolve extrinsic current noise limitations and conclude with a brief discussion of necessary improvements in future control systems to further enhance qubit lattice performance.

[1] Google Quantum AI and Collaborators. Quantum error correction below the surface code threshold. Nature 638, 920–926 (2025).

[2] D. Sank et al. Phys. Rev. Lett. **109**, 067001 (2012).

[3] J. Bylander et al. Nature Phys. vol. 7, pp. 565-570 (2011).