In 1962 Josephson predicted that an electric current can flow with no applied voltage through a thin insulating layer separating two superconductors. Since then, such "Josephson junction" has become has become the routinely used in many quantum electronic circuits (squids magnetometers, parametric amplifiers, superconducting qubits,...) and its use in the Volt metrology has helped reshape the International System of Units around quantum effects. Surprisingly, despite these long and successful applications in various areas, there are still subtle unresolved issues regarding how the junction interacts with its electromagnetic environment.
Here, we show experimentally that, contrary to what is long predicted and commonly believed, a Josephson junction connected to a resistor does not become insulating above some value of the resistance due to a dissipative quantum phase transition. We develop a new theoretical analysis which accounts for our observation and resolves previous inconsistencies in the theory. We also discuss why a phase transition is not observed in this system even though its presence was confirmed in systems thought to be equivalent.
We are hosting the Fall 2020 JQI Seminars virtually as Zoom meetings. JQI members and affiliates will receive a Zoom link in an email announcing each seminar. For those without access to Zoom, we will also be live streaming each seminar on YouTube. Once a seminar starts, you will find a link to the live stream on our YouTube page at https://www.youtube.com/user/JQInews