Curator's Take
AI Commentary
This article demonstrates that picosecond single‑flux‑quantum pulses from Josephson digital circuits can drive fluxonium qubits with gate fidelities exceeding 99.99 percent, overcoming the long‑standing difficulty of applying SFQ control to low‑frequency devices. By introducing a simple high‑frequency pulse‑packet scheme and a more aggressive phase‑shifted flux‑and‑charge sequence, the authors show both robust operation across parameter variations and substantially faster gates than previously possible. The work paves the way for fully cryogenic, scalable control electronics that could dramatically reduce wiring heat load and accelerate the integration of fluxonium into larger quantum processors.
— Mark Eatherly
Summary
We develop a control strategy for fluxonium qubits based on picosecond single-flux-quantum (SFQ) pulses generated by Josephson digital circuits. A major challenge is that SFQ protocols originally designed for transmon control become inefficient for low-frequency fluxonium. In this regime, the asymmetry of flux and charge couplings leads either to excessive leakage or excessively long gate times. We show that this limitation can be overcome by two complementary protocols. The first protocol employs high-frequency SFQ pulse packets applied through the flux channel, offering a simple, analytically transparent, and robust approach for high-fidelity single-qubit control. The second protocol combines phase-shifted flux and charge pulse sequences to enhance the resonant drive and reduce the gate duration. Multilevel simulations demonstrate single-qubit gate fidelities above $99.99\%$; the simpler protocol remains robust under moderate variations of qubit parameters and flux bias, while the combined protocol preserves high fidelity while substantially accelerating the gate. These results establish SFQ-based cryogenic control as a realistic route to fast, accurate, and scalable manipulation of fluxonium qubits.