When Noise is the Signal: Highlights in Qubit-Based Quantum Spectral Estimation

Abstract: Accurate characterization and control of open quantum systems exposed to realistic, spatio-temporally correlated noise are vital for exploiting the full potential of quantum technologies. Thanks to their exquisite sensitivity to the surrounding environment, qubits can be naturally considered as “spectrometers”, or sensors, of their own noise. I will first explain how formalizing this intuition has led, over the past decade, to the development of quantum control techniques - collectively referred to as “quantum noise spectroscopy” - for determining the noise spectral properties in a variety of qubit platforms. I will then highlight some of our contributions, by describing how protocols inspired by “spin-locking relaxometry” may be used to characterize noise that is both spatio-temporally correlated and non-classical in single- and two-qubit systems, and how these protocols can be made robust against state preparation and measurement errors. Finally, I will discuss limitations of standard frequency-based noise spectroscopy methods, and point to a recently introduced approach which leverages the notion of a “frame” to incorporate finite control resources from the outset - thereby allowing for a more efficient, “model-reduced” solution to the characterization and control problem of interest.