Quantum Capacitance Detectors with meV Resolution for Astroparticle Physics

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Determining the nature of dark matter, a mysterious ‘missing mass’ in the universe only presently observable by its large-scale gravitational effects, is crucial to furthering our understanding of both cosmology and fundamental forces and particles. One new well-motivated area to probe is in the ‘light’ dark matter regime, with particle masses roughly below that of a proton. This new regime necessitates new and sensitive techniques to detect potential interactions induced by these candidates in deep underground detectors. One such promising technology is Quantum Capacitance Detectors (QCDs), which are superconducting quantum mechanical circuitry that have heritage in the quantum computing world. This award will support a group at the California Institute of Technology to investigate this novel class of ‘qubit’ inspired particle detectors, Which have previously been demonstrated for other use cases. Additionally, the award will be used to broaden the participation of under-represented groups by targeted recruitment of undergraduate and high-school students to work on scientifically relevant projects, with an eye to producing open-access educational video-content in the process. The dark matter community considers the advancement of meV to eV energy scale particle detectors a critical requirement for future progress in the field. Specifically then, this award funds the development of detectors coupling interaction induced athermal phonon generation in crystalline silicon with a superconducting Cooper-pair box sensor. The latter is sensitive to the number parity of quasiparticles (broken Cooper-pair electrons) within its absorbing element. Such a scheme enables the literal counting of quasiparticles produced by single meV phonons and thus reach to the sub-GeV mass dark matter regime. The scope of the award includes for the design, fabrication, and testing of multiple generations of QCDs over a two-year pilot phase, with a roadmap of demonstrating eV and subsequently lower energy resolution on deposited energy within the crystalline substrate.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.