Study of Novel Low Noise Superconducting Mixers for Terahertz Radio Astronomy (TERAMIX)

Forskningsprojekt, 2012 – 2017

Terahertz heterodyne receivers are valuable tools for molecular gas spectroscopy both for space (radioastronomy, planetary science) and terrestrial applications. They provide both high resolution spectral data, as well as broad bandwidth line survey data. Due to the progress in device physics, such receivers can now reach several THz. At such high radio frequencies, neither electronic nor photonic approaches for THz detectors work, but rather a combination of both is required. Superconducting devices have proven to provide sensitivity levels close to the quantum limit, hf/k. Superconducting Hot- Electron Bolometers (HEB) based on ultrathin NbN and NbTiN films are currently the only devices which are used as mixers for frequencies above 1.2THz (SIS mixer limit). However, their speed (i.e. the instantaneous bandwidth) is limited by the finite electron energy relaxation rate, of 40-100 ps. It corresponds to the bandwidth of maximum 4-5GHz. Such applications in radio astronomy as extragalactic spectroscopy, molecular line survey require this bandwidth to be doubled to say at least. In this project we will investigate response rate in ultra thin MgB2 superconducting films. Preliminary investigation measured the electron-phonon interaction time as short as 1ps. Our recent data, point out on the response rate being limited by the phonon dynamic in the thick films. We will develop technology for ultrathin MgB2 film deposition, and processing THz nanobolometers.The response rate will be investigated with regards to the film parameters. In particularly, the phonon diffusion in superconducting nanobolometers will be studied in order to enhance the instantaneous bandwidth of MgB2 mixers. We estimate that the bandwidth of the novel THz detectors will be at least doubled compared to the existing once, providing completely new functionalities for THz radio astronomical receivers.