Al/AlO$_{\rm {x}}$/Al-Josephson-junction-based microwave generators for weak-signal applications below 100 mK

TL;DR

This paper develops and analyzes a Josephson junction-based microwave generator operating below 100 mK, capable of calibrating single-photon detectors in the 110-170 GHz range with tunable frequency and power.

Contribution

It introduces a novel on-chip microwave generator based on Al/AlO$_{ m {x}}$/Al Josephson junctions, with detailed theoretical modeling and experimental validation for weak-signal applications.

Findings

The generator operates effectively in the 110-170 GHz range.

Tuning of frequency and power is achieved via bias and magnetic field.

Predicted low linewidth and minimal black-body radiation emission.

Abstract

An application-specific Josephson generator is being developed as an on-chip calibration source for single-microwave-photon detectors operating below $T \sim $100 mK in the frequency range from 110 to 170 GHz. The targeted calibration power corresponds to the photon detection rate of 0.01 to 10 counts per second. We analyze the Josephson oscillations within the framework of the tunnel junction microscopic (TJM) model and find the corrections to be made to a standard RSJ model of the junction, operating as a quasi-monochromatic source of microwaves. Experimentally, we implemented a number of aluminium-based two-junction interferometers connected to the leads via microstripline resistors made of partly oxidized titanium films. The $I$-$V$ curves exhibit a behaviour ensuring generation of the microwave signal in the frequency range required. By setting the biasing point $\bar{V}$ and applying the magnetic field, one can tune the generator's frequency and power, respectively. A small oscillation linewidth, down to a few GHz, and a low level of black-body radiation emitted by hot parts of the circuit are predicted, using the experimental parameters.