Presentation Information
[ED7-01-INV]High-Fidelity Qubit Control with Single-Flux-Quantum Circuits
*Zhirong Lin1 (1. Shanghai Institute of Microsystem and Information Technology, CAS (China))
Keywords:
Single-Flux-Quantum Electronics,Superconducting Qubit,Qubit Gate Fidelity,Cryogenic Qubit Control
Superconducting circuits are a leading platform for large-scale quantum processors, but scaling to thousands of qubits is hindered by the extensive room-temperature hardware required for classical microwave control. Single-flux-quantum (SFQ) electronics offer a power-efficient, integrable alternative for cryogenic control. However, existing on-chip integration SFQ controllers suffer from fidelity degradation due to SFQ-induced quasiparticle poisoning and parasitic antenna coupling[1-2]. We introduce a spatially decoupled SFQ control architecture that overcomes these issues. Our design integrates an on-chip low-pass filter for spectral purity and an impedance-matching network optimized for millikelvin operation, effectively isolating the qubit from the SFQ driver. Operating within a dilution refrigerator, our controller achieves a single-qubit gate fidelity of 99.9%. This high performance is enabled by carefully shaped control pulses (60-ns rise time, -77 dBm peak power into a 50 Ω load) and effective suppression of high-frequency noise, which mitigates both quasiparticle poisoning and antenna coupling. Crucially, we observe no degradation in qubit coherence times and single-qubit gate fidelity compared to control with conventional room-temperature electronics. We further demonstrate the viability of our architecture by implementing an SFQ-activated two-qubit gate for transmon qubits [3]. Our work establishes a scalable pathway for integrating high-fidelity quantum processors and their control systems at millikelvin temperatures. By enabling the flexible cryogenic deployment of SFQ electronics without compromising qubit performance, this architecture represents a critical step toward building practical, large-scale quantum computers.
Figure 1 Single-qubit gate fidelity measurement with a spatially decoupled SFQ controller
References 1) K. Liu et al. Physical Review B Vol 108, pp064512, 2023
2) J. Bernhardt et al. arXiv:2503.09879, 2025
3) Y. F. Wang et al. Physical Review Applied Vol.19, p044031, 2023
Figure 1 Single-qubit gate fidelity measurement with a spatially decoupled SFQ controller
References 1) K. Liu et al. Physical Review B Vol 108, pp064512, 2023
2) J. Bernhardt et al. arXiv:2503.09879, 2025
3) Y. F. Wang et al. Physical Review Applied Vol.19, p044031, 2023