Development of highly sensitive nanoscale transition edge sensors for gigahertz astronomy and dark matter search

Terahertz (THz) and sub-terahertz (sub-THz) band detection has a key role in both fundamental interactions physics and technological applications, such as medical imaging, industrial quality control, and homeland security. In particular, transition edge sensors (TESs) and kinetic inductance detectors (KIDs) are the most employed bolometers and calorimeters in the THz and sub-THz band for astrophysics and astroparticles research. Here, we present the electronic, thermal, and spectral characterization of an aluminum/copper bilayer sensing structure that, thanks to its thermal properties and a simple miniaturized design, could be considered a perfect candidate to realize an extremely sensitive class of nanoscale TES (nano-TES) for the giga-terahertz band. Indeed, thanks to the reduced dimensionality of the active region and the efficient Andreev mirror heat confinement, our devices are predicted to reach state-of-the-art TES performance. In particular, as a bolometer the nano-TES is expected to have a noise equivalent power of5 x10- 20W/Hz and a relaxation time ofsimilar to 10ns for the sub-THz band, typical of cosmic microwave background studies. When operated as a single-photon sensor, the devices are expected to show a remarkable frequency resolution of 100GHz, pointing toward the necessary energy sensitivity requested in laboratory axion search experiments. Finally, different multiplexing schemes are proposed and sized for imaging applications.