Low-noise readout of superconducting bolometers based on electrothermal feedback

We have developed a simple room-temperature readout for superconducting bolometers and calorimeters. Due to electro-thermal feedback, the bolometer can be noise-matched with the readout amplifier. The constructed amplifier consists of low-noise field-effect transistors, and voltage bias is actively provided by electrical feedback. According to our measurements on superconducting vacuum-bridge bolometers, the total noise is limited by the bolometer phonon and Johnson noise characterized by a critical temperature of 8.5 K. We show that, with proper sensor design, it is possible to reach the photon noise limit in video-rate submillimetre imaging applications