Abstract: The discovery of superconductivity in 1911 by K.Onnes was based on the striking observation of a zero resistivity in some metals below a certain temperature. This unique property explains why superconductors are at the heart of circuit QED : one can fabricate superconducting cavities with low losses, and create quantum superpositions with long coherence time thanks to a non-dissipative and non-linear element : the Josephson junction. One can then wonder what happens if one embeds a superconductor in a circuit of high impedance. Can superconductivity be able to overcome the large voltage fluctuations imposed by that environment ? It was recognized long ago that in this regime, the phase of the order parameter starts to become ill-defined, a phenomenon that manifests itself by the occurrence of jumps of 2 pi. These so called "phase slips" have been predicted to have strong consequences on superconductivity.
In this talk, I will focus on two theoretical predictions : the Schmid-Bulgadaev dissipative quantum phase transition [1] and the Mooij-Nazarov phase slip qubit [2]. Based on microwave experiments, I will argue that the physics is perhaps more complicated [3] (or simpler [4]) than what was initially thought.
[1] Albert Schmid, Phys. Rev. Lett. 51 (1983) [2] Mooij and Nazarov, Nat. Phys. 2 (2006)[3] Hélène le Sueur et. al., arXiv:1810.12801 (2018)[4] Anil Murani et. al., arXiv:1905.01161 (2019)
Host: M. Aspelmeyer