CAREER: Characterization of Material Defects Using Broadband Two-Level-System Spectroscopy

Nontechnical Description This CAREER project advances the understanding of atomic-scale defects that limit the performance of next-generation materials in quantum electronics. These defects, known as two-level systems, can absorb energy and create noise in materials at very low temperatures. The research uses Broadband Cryogenic Transient Dielectric Spectroscopy (BCTDS), a measurement technique developed by the PI. The BCTDS technique enables direct probes of defects in quantum materials such as two-level systems. By connecting defects to how the materials are made and processed, the project helps the research community identify which materials host harmful defects, their nature, and how to avoid them. The activity also produces open data sets, analysis tools, and teaching materials that make it easier for students, educators, and researchers at a wide range of institutions to explore real data from quantum materials. Outreach efforts include interactive online modules, a podcast that highlights the people and processes behind the research, and an illustrated children’s book that explains the hidden structure inside materials. These activities make advanced materials research more accessible to entering undergraduates and help prepare a new generation of students to work at the intersection of materials science and modern quantum engineering. Technical Description This project establishes Broadband Cryogenic Transient Dielectric Spectroscopy as a quantitative, modular platform for characterizing two-level systems and related point defects in materials that support semiconducting and superconducting technologies. Two-level system defects are dominant sources of microwave dielectric loss and noise in thin films, interfaces, and bulk substrates. Yet their atomistic structure and dependence on processing history remain poorly understood. Conventional probes based on resonators and quantum bits are narrow band, spatially localized, and typically infer defects only indirectly through device coherence. In contrast, BCTDS uses a three-dimensional waveguide to deliver strong, broadband microwave pulses at cryogenic temperatures and measures the transient dielectric response across gigahertz bandwidths, enabling direct extraction of effective Rabi frequencies, dipole moments, and interaction strengths. The research establishes this technique as an in-situ probe throughout material processing by incorporating tunable microwave polarization, static electric and magnetic field biasing, optical access, and cryogenic positioning to perform longitudinal studies through multiple processing steps and to establish causal relationships between processing and defect properties. The research team also builds an open database that links BCTDS spectra to detailed processing metadata and material stacks. In parallel, the team will model the materials using processing-aware density functional theory and effective spin models that are compared to experiment to identify likely defect species and to connect their spectroscopic fingerprints to specific structural motifs and processing conditions. Together, these efforts establish quantitative relationships between processing, defect properties, and dielectric loss, provide design rules for low-defect materials and interfaces, and enable the community to identify low-loss material stacks and processing conditions without extensive trial-and-error studies. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2540460 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT,01002930DB NSF RESEARCH & RELATED ACTIVIT,01002829DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Mattias Fitzpatrick | Institution: Dartmouth College, HANOVER, NH | Award Amount: $530,000 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2540460 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2540460.html