Physics Colloquium with Karthik Ramanathan on Direct Detection of Dark Matter

Determining the nature of dark matter (DM), a mysterious ‘missing mass’ in the universe, is crucial to completing our models of cosmology and high-energy physics. However, repeated null searches for the most favored DM candidates has motivated a community re-evaluation of the theoretical biases towards this parameter space. Two recent areas of interest, among the many decades of potential DM masses, are particle-like ‘light DM’ with masses less than a GeV and wave-like candidates of O(10) ueV. In this talk, I will discuss R&D work and experiments that seek to probe both avenues. Notably, experiments targeting these regimes can benefit from overlapping advances in superconducting tools and techniques that exploit quantum phenomena. In the case of wave-like DM I will present leading constraints from a broadband search for Hidden Photon DM, which uses a Kinetic Inductance Parametric Amplifier to achieve ‘quantum limited’ noise performance. For light DM, I will touch on the challenges in measuring their meV-to-eV scale energy deposits within a crystalline target and present designs & roadmaps for phonon-mediated sensors with the potential to do so. These include demonstrated Kinetic Inductance Detectors and R&D work in realizing Quantum Capacitance Detectors (QCDs). QCDs are effectively ‘qubits’ from the quantum computing world and, ambitiously, should allow for the literal counting of quasiparticles within a superconducting absorber as produced by single meV phonons.