Increasing the degree of control over physical qubits is a crucial component of quantum computing research. We report a superconducting qubit of fluxonium type with the Ramsey coherence time reaching T2∗=1.48±0.13ms, which exceeds the state of the art value by an order of magnitude. As a result, the average single-qubit gate fidelity grew above 0.9999, surpassing, to our knowledge, any other solid-state quantum system. Furthermore, by measuring energy relaxation of the parity-forbidden transition to second excited state, we exclude the effect of out-of-equilibrium quasiparticles on coherence in our circuit. Combined with recent demonstrations of two-qubit gates on fluxoniums, our result paves the way for the next generation of quantum processors.
@article{arxiv.2103.08578,
title = {Millisecond coherence in a superconducting qubit},
author = {Aaron Somoroff and Quentin Ficheux and Raymond A. Mencia and Haonan Xiong and Roman V. Kuzmin and Vladimir E. Manucharyan},
journal= {arXiv preprint arXiv:2103.08578},
year = {2021}
}