Listening to Quantum Materials Using Nonlinear Noise Spectroscopy

Quantum materials such as superconductors, magnets, and topological insulators have great potential for realizing advanced electronic and computing devices, but characterizing and understanding these materials has remained a challenge. Conventional tools like nonlinear optics or transport are often difficult to employ or interpret since they are severely limited in spatial resolution. Especially given the rise of two-dimensional moiré materials, it is more important than ever to find probes which can resolve the rich spatial and dynamical correlations present in these materials. One such technique is noise magnetometry, which utilizes nanoscale spin qubits to map out the landscape of magnetic fluctuations in a material with spatial resolution on the order of 10’s of nm. In this talk I will provide a theoretical example of how nanoscale noise spectroscopy can be used to uncover superconducting fluctuations in a two-dimensional material, before highlighting the need for nonlinear probes. I will then unveil a new set of protocols which can be used to study nonlinear correlations in the magnetic noise, blending the crisp spatial resolution of noise spectroscopy with the insights of nonlinear spectroscopy. As an example, I will show how this technique can be used to study critical magnetic fluctuations in a two-dimensional material, such as a Van der Waals magnet, and how cooperative noise onsets near a phase transition. I will then conclude by providing an outlook on the next generation of probes which can use multiple qubits to detect spatially non-local correlations, and what we can look for using these tools.