Curator's Take
This article extends the analytical fidelity‑reduction framework from static Markovian noise to the realistic case where dissipation varies during a gate, filling a gap that has limited error budgeting for tunable superconducting processors. By deriving explicit bounds for adiabatic CZ gates and showing how flux‑dependent loss and qubit‑coupler hybridization can erode fidelity, it connects directly to recent efforts to push two‑qubit gate errors below the 0.1 % threshold on platforms such as Google’s Sycamore and IBM’s Eagle. The results give hardware designers a concrete tool for optimizing pulse schedules and coupler architectures, though the bounds assume weak coupling and may need refinement for strongly non‑Markovian environments.
— Mark Eatherly
Summary
As quantum-computing platforms are susceptible to noise, the fidelity of quantum operations is limited by decoherence. Understanding this limitation is crucial for building utility-scale quantum processors. In previous works [Phys. Rev. Lett. 129, 150504 (2022); Quantum 9, 1684 (2025)], we presented analytical formulae for the average gate fidelity of multi-qubit operations under static Markovian noise processes, including operations that temporarily leave the computational subspace. However, some quantum-computing architectures dynamically modulate qubit or coupler frequencies to implement two-qubit gates, e.g., baseband flux gates; such modulation can lead to dissipation rates varying in time. In this Letter, we therefore generalize the fidelity-reduction formulae to encompass time-dependent dissipation. Applying our generalized formula, we obtain a fidelity bound for adiabatic operations and demonstrate that flux-dependent noise sensitivity, combined with qubit-coupler hybridization, significantly reduces the fidelity of adiabatic controlled-Z (CZ) gates in superconducting quantum computers. Our work thus provides essential theoretical tools for evaluating error budgets and optimizing the design of quantum operations in tunable quantum-computing architectures, and may also find applications in quantum-sensing and quantum-communication protocols that are affected by time-dependent dissipation.