NITROGEN-VACANCY CENTER MAGNETOMETRY FOR CONDENSED MATTER SYSTEMS

Abstract

Nitrogen-vacancy (NV) centers in diamond are atomic-scale quantum sensors that combine nanoscale spatial resolution with quantitative magnetic-field readout under ambient conditions. This dissertation develops and applies NV magnetometry to three problems in nanoscale magnetism, in each case extending the sensing technique and using it to access physics that is difficult to reach by other means.

We first use spatially resolved NV magnetometry to image the nonlinear scattering dynamics of driven magnons in a yttrium iron garnet (YIG) thin film. A two-tone wave-mixing protocol isolates the elementary four-magnon interaction and extracts its strength directly from the spatial growth profile of the scattering product. Under strong single-tone driving, the system organizes into a spontaneous cascade of discrete, power-tunable parametric resonances whose growth is maximized where the magnon group velocity vanishes, resolving the pre-thermal approach to equilibrium as a structured hierarchy of discrete scattering channels rather than a diffusive continuum.

Second, we introduce a spectrum analyzer based on qubit dressed states that extends NV noise magnetometry beyond the conventional Rabi-rate limit. Embedding an off-resonant microwave probe in a dynamical-decoupling sequence uses the AC Stark shift to parametrically mix the probe with the target noise, so the accessible center frequency is set by the probe rather than the pulse repetition rate. We validate the method against a commercial spectrum analyzer and use it to extract the thermal magnon noise spectrum and group velocity in a YIG thin film at frequencies hundreds of megahertz above the NV resonance.

Third, we apply NV-ensemble magnetic-field imaging to artificial spin ice for the first time, mapping the stray fields of a pinwheel array through a field-driven reversal at room temperature with a diamond microchip placed directly on the sample. The maps resolve the full reversal of the superferromagnetic domain structure, from a uniform configuration through the nucleation, growth, and coalescence of mesoscopic domains to the reversed state, and show that the reversal is stochastic yet nucleates at the same locations.

Together, these projects extend NV magnetometry along three axes: spatial imaging of nonlinear many-body dynamics, the frequency range of noise spectroscopy, and confocal imaging of patterned magnetic systems. They help to establish NV magnetometry as a quantitative, non-invasive probe of magnetism at the nanoscale.