• DOI:10.1103/PHYSREVX.11.011010
• Corpus ID: 211296872

Universal Fast-Flux Control of a Coherent, Low-Frequency Qubit

@article{Zhang2020UniversalFC,
  title={Universal Fast-Flux Control of a Coherent, Low-Frequency Qubit},
  author={Helin Zhang and Srivatsan Chakram and Tanay Roy and Nathan Earnest and Yao Lu and Ziwen Huang and Daniel Weiss and Jens Koch and David I. Schuster},
  journal={arXiv: Quantum Physics},
  year={2020}
}

• Helin Zhang, S. Chakram, +6 authors D. Schuster
• Published 24 February 2020
• Physics
• arXiv: Quantum Physics

The \textit{heavy-fluxonium} circuit is a promising building block for superconducting quantum processors due to its long relaxation and dephasing time at the half-flux frustration point. However, the suppressed charge matrix elements and low transition frequency have made it challenging to perform fast single-qubit gates using standard protocols. We report on new protocols for reset, fast coherent control, and readout, that allow high-quality operation of the qubit with a 14 MHz transition frequency, an order of magnitude lower in energy than the ambient thermal energy scale. We utilize higher levels of the fluxonium to initialize the qubit with $97$\% fidelity, corresponding to cooling it to $190~\mathrm{\mu K}$. We realize high-fidelity control using a universal set of single-cycle flux gates, which are comprised of directly synthesizable fast pulses, while plasmon-assisted readout is used for measurements. On a qubit with $T_1, T_{2e}\sim$~300~$\mathrm{\mu s}$, we realize single-qubit gates in $20-60$~ns with an average gate fidelity of $99.8\%$ as characterized by randomized benchmarking.