Ramsey oscillations typically exhibit an exponential decay envelope due to environmental noise. However, recent experiments have observed nonmonotonic Ramsey fringes characterized by beating patterns, which deviate from the standard behavior. These beating patterns have primarily been attributed to charge-noise fluctuations. In this paper, we investigate the flux-noise origin of these nonmonotonic Ramsey fringes in frequency-tunable transmon qubits. We develop a random telegraph noise (RTN) model to simulate the impact of telegraph-like flux-noise sources on Ramsey oscillations. Our simulations demonstrate that strong flux-RTN sources can induce beating patterns in the Ramsey fringes, showing excellent agreement with experimental observations in transmon qubits influenced by electronic environment-induced flux-noise. Our findings provide valuable insights into the role of flux-noise in qubit decoherence and underscore the importance of considering flux-noise RTN when analyzing nonmonotonic Ramsey fringes.
@article{arxiv.2502.05499,
title = {Telegraph flux noise induced beating Ramsey fringe in transmon qubits},
author = {Zhi-Hao Wu and Ling-Xiao Lei and Xin-Fang Zhang and Shi-Chuan Xue and Shun Hu and Cong Li and Xiang Fu and Ping-Xing Chen and Kai Lu and Ming-Tang Deng and Jun-Jie Wu},
journal= {arXiv preprint arXiv:2502.05499},
year = {2025}
}