NQCP Life in Quantum - Ass. Professor Morten Kjaergaard, NQCP

Parameter estimation, gate calibration and performance benchmarking on millisecond timescales with superconducting qubits

I will discuss recent results from the NQCP superconducting C&R team on developing a tight control-and-feedback loop between rapid FPGA-based advanced logic and superconducting qubit control, which enables qubit characterization, optimization, gate benchmarking, and parameter estimation on millisecond wall-clock timescales. We developed a suite of sparse-sampling and on-FPGA inference methods, including efficient estimators for exponential and sinusoidal response functions as well as on-FPGA implementations of Nelder–Mead optimization, golden-section search and an adaptive Bayesian updating algorithm. With this approach, we estimate T1 in a few milliseconds, optimize readout parameters in roughly 100 ms, optimize pulse amplitudes in 1 ms, perform Clifford randomized benchmarking in 107 ms, and sustain more than 74,000 consecutive recalibrations during a 6-hour closed-loop run. These approaches enable in situ recalibration that can track evolving qubit dynamics and enable new approaches to maximizing superconducting qubit processor performance towards QEC applications.

 Relevant papers: arXiv:2602.11912 and https://journals.aps.org/prx/abstract/10.1103/gk1b-stl3