Measuring Environmental Quantum Noise Exhibiting a Nonmonotonic Spectral Shape

Quantum noise spectroscopy is an important tool for understanding the ubiquitous noise sources in quantum systems. Traditional spectroscopic methods are usually inefficient in measuring noise spectra that are broadband and decay nonmonotonically (exhibiting resonances, for example). Here a fresh approach uses a continuous driving method called gDYSCO. Performance of the continuous and traditional pulsed sequences is quantified analytically and numerically, and compared, revealing gDYSCO's advantages in reconstructing nontrivial spectral features. Experiments confirm the findings, pointing to improved understanding and handling of quantum noise sources through this superior technique.