Graphene Josephson Junction-based Adjustable Power and Frequency Microwave Generator

Graphene, a monolayer of carbon atoms known for its exceptional electron transport properties, has demonstrated considerable promise in applications involving Josephson junctions and the superconducting proximity effect. Its gate-tunable charge density enables precise control over the number of conduction channels, directly influencing the critical current of Josephson junctions. Josephson junctions, formed by weakly coupling two superconductors with a nanoscale insulator or mesoscopic conductor, emit microwaves when subjected to a DC voltage, owing to the AC Josephson effect, 2eV/ℏ = dφ/dt corresponding to 0.483 GHz/μV. In this study, we implemented a GHz-range microwave generator composed of graphene-based Josephson junctions and shunt resistors. The generated signals in our system exhibited power proportional to the square of the critical current and matched the theoretical power predictions within the same order of magnitude. This study focuses on manipulating graphene's gate-tunability to develop a cryogenic microwave generator capable of adjusting power and frequency. The proposed system is particularly suitable for integration into cryogenic high-frequency measurement setups, where local generation of microwaves reduces dependence on external signal sources and minimizes losses in long coaxial transmission lines. Furthermore, the cryogenically generated signals are inherently free from thermal noise and provide stable, high-quality microwave excitation, thereby offering a valuable tool for advanced low-temperature spectroscopy and high-frequency quantum transport experiments.