Ultra-sensitive hot-electron nanobolometers for THz astrophysics

The background-limited spectral imaging of the early Universe requires terahertz (THz) detectors with the sensitivity 2-3 orders of magnitude better than that of the state-of-the-art bolometers. To realize this sensitivity without sacrificing the operating speed, the sensing element of a bolometric detector should have an exceptionally high thermal isolation from the environment combined with an ultrasmall heat capacity. We have demonstrated that this goal can be achieved by realizing a superconducting hot-electron nanobolometer whose design blocks photon and phonon energy exchange through its contact leads. The remaining coupling due to electron-phonon interaction provides thermal control at a level of one thousandth of the quantum of thermal conductance G_Q ap 1 [pW/K] times T. These hot-electron nanobolometers with a heat capacity of ~ 0.1 aJ/K will be sufficiently sensitive for registration of single THz photons. These devices are very promising for submillimeter astronomy and other applications based on quantum calorimetry and photon counting.