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Efe Gümüs presents

 Calorimetry of a phase slip in a Josephson junction

Friday, April 28th 2023 at 10:00 am

Seminar room – Building A – CNRS

The defence will be in French. 



Magnetic flux which is a continuous quantity in the classical world, becomes quantized when confined at the center of a superconducting loop. A quantum of flux can penetrate in/out of the loop under certain conditions via thermal activation or macroscopic quantum tunneling. Josephson junction, a key building block of the superconducting quantum devices, provides a straightforward implementation of this event where the transfer of a Cooper pair between the two superconducting reservoirs is visualized as the transverse tunneling of the magnetic flux quantum.

By bringing these concepts together in a superconducting quantum interference device (SQUID), it becomes possible to generate a so-called phase slip where a flux quantum enters/leaves the loop and the superconducting phase winds by 2π in a deterministic manner. This event is of dissipative nature when the SQUID operates in the strongly screening (hysteretic) regime therefore can be detected via calorimetry methods. In this thesis, we demonstrate the real time detection of a phase slip which is manifested as the abrupt increase and the subsequent relaxation of the electronic temperature of the Normal island placed in the SQUID loop as a weak link. The system is embedded in a microwave resonator. The phase slips are generated by nanosecond pulses sent on an on- ship flux line, and the temperature excursion is read via the variation of the transmitted power by exploiting the proximity effect as a secondary thermometer.

By addressing the observation of an elementary dissipative event, this work provides an insight on the role of dissipation ubiquitous in superconducting devices and showcases the potential use of the fast nano-calorimeters in the field of quantum sensors.