Bolometric detection of Josephson inductance in a highly resistive environment

• Published in: Nature communications 2023-12, Vol.14 (1), p.7924-7924, Article 7924
• Main Authors: Subero, Diego, Maillet, Olivier, Golubev, Dmitry S., Thomas, George, Peltonen, Joonas T., Karimi, Bayan, Marín-Suárez, Marco, Yeyati, Alfredo Levy, Sánchez, Rafael, Park, Sunghun, Pekola, Jukka P.
• Format: Article
• Language: English
• Subjects: 639/766/1130/1064; 639/766/119/2795; Charge transport; Cooper pairs; Coupling; Critical current (superconductivity); Fluctuations; Heat transport; High frequencies; Humanities and Social Sciences; Inductance; Inductors; Josephson junctions; multidisciplinary; Phase transitions; Physics; Science; Science (multidisciplinary); Shunt resistance
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-43668-3

The Josephson junction is a building block of quantum circuits. Its behavior, well understood when treated as an isolated entity, is strongly affected by coupling to an electromagnetic environment. In 1983, Schmid predicted that a Josephson junction shunted by a resistance exceeding the resistance quantum R Q  =  h /4 e 2  ≈ 6.45 kΩ for Cooper pairs would become insulating since the phase fluctuations would destroy the coherent Josephson coupling. However, recent microwave measurements have questioned this interpretation. Here, we insert a small Josephson junction in a Johnson-Nyquist-type setup where it is driven by weak current noise arising from thermal fluctuations. Our heat probe minimally perturbs the junction’s equilibrium, shedding light on features not visible in charge transport. We find that the Josephson critical current completely vanishes in DC charge transport measurement, and the junction demonstrates Coulomb blockade in agreement with the theory. Surprisingly, thermal transport measurements show that the Josephson junction acts as an inductor at high frequencies, unambiguously demonstrating that a supercurrent survives despite the Coulomb blockade observed in DC measurements. The predicted dissipative quantum phase transition in a Josephson junction coupled to resistive environment has been examined in recent experiments. In a heat transport experiment, Subero et al. show that the junction acts as an inductor at high frequencies, while DC charge transport confirms insulating behaviour.