# Quantum circuits with SINIS structures

## TL;DR

SINIS structures are used to create sensitive cryogenic devices capable of detecting microwave radiation with high responsivity.

## Contribution

The paper presents SINIS arrays with improved sensitivity for detecting 90 GHz radiation at the BTA telescope.

## Key findings

- SINIS devices achieved a best responsivity of 72000 A/W at 350 GHz.
- Voltage responsivity reached 3.9 × 10^9 V/W with black body radiation.
- SINIS arrays are designed for 90 GHz detection with noise equivalent power below 10^-16 W·Hz^-1/2.

## Abstract

The superconductor–insulator–normal metal–insulator–superconductor (SINIS) tunnel junction structure is the basic building block for various cryogenic devices. Microwave detectors, electron coolers, primary thermometers, and Aharonov–Bohm interferometers have been fabricated by various methods and measured at temperatures down to 100 mK. The manufacturing methods included Dolan-type shadow evaporation, Manhattan-type shadow evaporation, and magnetron sputtering with selective etching of superconducting and normal metal electrodes. Improvement in ultimate sensitivity is achieved by suspending the absorber above the substrate. Best responsivity of up to 30 electrons per photon at a frequency of 350 GHz, or 72000 A/W, and voltage responsivity up to 3.9 × 109 V/W were obtained with a black body radiation source and series of band-pass filters. The specially designed SINIS arrays are intended to detect 90 GHz radiation at the “Big Telescope Alt-azimuthal” (romanized Russian: “Bolshoi Teleskop Alt-azimutalnyi”, BTA) with noise equivalent power of less than 10−16 W·Hz−1/2. The receiver in a 3He cryostat with an optical window was mounted at the Nasmyth focus of the BTA and tested at a temperature of 260 mK with a IMPATT diode radiation source.