Digital Control of a Superconducting Qubit Using a Josephson Pulse Generator at 3 K

Abstract

Scaling of quantum computers to fault-tolerant levels relies critically on the integration of energy-efficient, stable, and reproducible qubit control and readout electronics. In comparison to traditional semiconductor-control electronics (TSCE) located at room temperature, the signals generated by rf sources based on Josephson-junctions (JJs) benefit from small device sizes, low power dissipation, intrinsic calibration, superior reproducibility, and insensitivity to ambient fluctuations. Previous experiments to colocate qubits and JJ-based control electronics have resulted in quasiparticle poisoning of the qubit, degrading the coherence and lifetime of the qubit. In this paper, we digitally control a 0.01-K transmon qubit with pulses from a Josephson pulse generator (JPG) located at the 3-K stage of a dilution refrigerator. We directly compare the qubit lifetime T_{1}, the coherence time T_{2}^{∗}, and the thermal occupation P_{th} when the qubit is controlled by the JPG circuit versus the TSCE setup. We find agreement to within the daily fluctuations of ±0.5μs and ±2μs for T_{1} and T_{2}^{∗}, respectively, and agreement to within the 1% error for P_{th}. Additionally, we perform randomized benchmarking to measure an average JPG gate error of 2.1×10^{−2}. In combination with a small device size (<25mm^{2}) and low on-chip power dissipation (≪100μW), these results are an important step toward demonstrating the viability of using JJ-based control electronics located at temperature stages higher than the mixing-chamber stage in highly scaled superconducting quantum information systems.