High-Order Qubit Dephasing at Sweet Spots by Non-Gaussian Fluctuators: Symmetry Breaking and Floquet Protection

Although the Gaussian noise assumption is widely adopted in studying qubit decoherence, non -Gaussian noise sources have been detected in many qubits. Further understanding and mitigating the distinctive decoherence effect of the non-Gaussian noise remain critical. Here, we study the qubit dephasing caused by non-Gaussian fluctuators, and predict a symmetry-breaking effect that is unique to non-Gaussian noise. This broken symmetry results in an experimentally measurable mismatch between the extremum points of the dephasing rate and qubit frequency, which demands extra carefulness in char-acterizing the noise and locating the optimal working point. To further enhance the coherence time, we propose suppressing the second-order derivative of the qubit frequency by Floquet engineering. Our sim-ulation on a tunable and gapped two-level quantum system, with the parameters from a heavy fluxonium, shows an order-of-magnitude improvement of the dephasing time, even after including the drive noise.

Automated summary

Although the Gaussian noise assumption is widely used in studying qubit decoherence, non-Gaussian noise sources have been found in many qubits. This study investigates qubit dephasing caused by non-Gaussian fluctuators and predicts a unique symmetry-breaking effect. The study also proposes a method to enhance coherence time by suppressing the second-order derivative of the qubit frequency using Floquet engineering.