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 of 5 Â 10 À20 W/ ffiffiffiffiffiffi Hz p and a relaxation time of 10 ns 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 100 GHz, pointing toward the necessary energy sensitivity requested in laboratory axion search experiments. Finally, different multiplexing schemes are proposed and sized for imaging applications.

Single-photon detectors and bolometers represent the bridge between different topics in science, such as quantum computation, astronomy, particle physics, and biology. Nowadays, superconducting bolometers and calorimeters are the most-sensitive detectors in the terahertz and subterahertz bands. Here, we propose and demonstrate a Josephson escape sensor (JES) that could find natural application in astrophysics. The JES is composed of a fully superconducting one-dimensional Josephson junction, whose resistance-versus-temperature characteristics can be precisely controlled by a bias current. Therefore, differently from traditional superconducting detectors, the JES sensitivity and working temperature can be in situ simply and finely tuned depending on the application requirements. A JES bolometer is expected to show an intrinsic thermal-fluctuation-noise noise-equivalent power on the order of 10 −25 W/Hz 1/2 , while a JES calorimeter could provide a frequency resolution of about 2 GHz, as deduced from the experimental data. In addition, the sensor can operate at the critical temperature (i.e., working as a conventional transition-edge sensor), with a noise-equivalent power of approximately 6 × 10 −20 W/Hz 1/2 and a frequency resolution of approximately 100 GHz.

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