Curator's Take
AI Commentary
This article shows how periodic‑drive (Floquet) engineering can turn a simple pulse train into a systematic toolbox for synthesising high‑fidelity two‑qubit gates and fast excitation‑transfer across superconducting chains up to seven sites, delivering gate times (~170 ns) that sit comfortably below typical T₁ lifetimes of fixed‑frequency transmons. By combining analytic Floquet resonance conditions with CMA‑ES optimisation, the authors achieve an iSWAP implementation comparable to state‑of‑the‑art hardware while exposing a clear scaling pathway for larger linear arrays. The work also highlights a practical limitation—sub‑percent static disorder can degrade performance because of spectral crowding—pointing toward closed‑loop topologies or adaptive calibration as needed next steps.
— Mark Eatherly
Summary
Precise control of multi-qubit architectures remains a critical bottleneck in superconducting quantum processors. In this work, we investigate the synthesis of high-fidelity quantum operations and state transfer protocols within an extended superconducting linear chain, scaling from three to seven sites. Using Floquet theory, we model the periodic drive as a train of delta-like pulses, mapping the quantum control problem onto quasi-energy resonance conditions. Combining the Baker-Campbell-Hausdorff expansion with Floquet spectral decomposition, we analytically identify optimal driving parameters, refined via the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). In the three-qubit architecture, this enables high-fidelity synthesis of the iSWAP gate. Extending to a seven-site chain, we implement periodic trains of finite-width Gaussian pulses to activate distinct double-excitation transport channels with ultra-short gate durations t_gate (~170 ns). This achieves a clear scale separation from energy-relaxation times (T1) typical of fixed-frequency transmon devices with tunable couplers, such as IBM Quantum hardware. Finally, we benchmark stability under realistic imperfections, revealing a heightened sensitivity to static parameter disorder at the sub-percent level (eta ~ 10^-3) driven by spectral crowding, and discuss how closed-loop topologies could mitigate this constraint. This framework bridges time-periodic control theory and practical quantum gate engineering.