We introduce Cryoscope, a method for sampling on-chip baseband pulses used to dynamically control qubit frequency in a quantum processor. We specifically use Cryoscope to measure the step response of the dedicated flux control lines of two-junction transmon qubits in circuit QED processors with the temporal resolution of the room-temperature arbitrary waveform generator producing the control pulses. As a first application, we iteratively improve this step response using optimized real-time digital filters to counter the linear-dynamical distortion in the control line, as needed for high-fidelity, repeatable one- and two-qubit gates based on dynamical control of qubit frequency.
@article{arxiv.1907.04818,
title = {Time-domain characterization and correction of on-chip distortion of control pulses in a quantum processor},
author = {M. A. Rol and L. Ciorciaro and F. K. Malinowski and B. M. Tarasinski and R. E. Sagastizabal and C. C. Bultink and Y. Salathe and N. Haandbaek and J. Sedivy and L. DiCarlo},
journal= {arXiv preprint arXiv:1907.04818},
year = {2025}
}