High quality epitaxial NbN/MgO/NbN Josephson junctions have been realized with MgO barriers up to a thickness of d=1 nm. The junction properties coherently scale with the size of barrier, and low critical current densities down to 3 A/cm2 have been achieved for larger barriers. In this limit, junctions exhibit macroscopic quantum phenomena for temperatures lower than 90 mK. Measurements and junction parameters support the notion of a possible use of these devices for multiphoton quantum experiments, taking advantage of the fast non equilibrium electron-phonon relaxation times of NbN.
@article{arxiv.1111.5091,
title = {Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions with low critical current density},
author = {Luigi Longobardi and Davide Massarotti and Giacomo Rotoli and Daniela Stornaiuolo and Gianpaolo Papari and Akira Kawakami and Giovanni Piero Pepe and Antonio Barone and Francesco Tafuri},
journal= {arXiv preprint arXiv:1111.5091},
year = {2013}
}