Dephasing-Robust Characterization of Temporally-Correlated Qubit Control Noise*

Precise control of quantum systems is a requirement for quantum technologies spanning fields from quantum metrology to quantum computing. A major factor limiting control fidelity is noise due to fluctuations in control fields.  To design optimally robust control sequences, it is first necessary to have a high-accuracy characterization of the statistical properties of control noise. Previous approaches to characterize control noise are limited by their vulnerability to low-frequency dephasing noise, which can overwhelm the target control noise signal and prevent reliable characterization. In this work, we apply optimized narrowband quantum control sequences to probe fine spectral features of amplitude control noise while simultaneously suppressing dephasing noise. This extends the spectroscopy of control noise to experimentally relevant settings where dephasing is strong relative to control noise, such as superconducting qubits.