PhD defense of Ugur YILMAZ

Josephson junction, ADC, SQUID, Asynchronous, Mixed signal

Abstract:
Digital superconducting electronics based on the SFQ (Single Flux Quantum) architecture enables logical operations with a magnetic flux quantum Φ0 (h/2e = 2.07 mV.ps) which is propagated, stored or released in the form of a voltage pulse of a few picoseconds of quantized area. This disruptive electronics allows logic operations with a switching energy of the order of 10^-19 J and switching frequencies in the order of 40 to 100 GHz, under the assumption of a fabrication technology having a sufficiently high characteristic RNIC voltage.
This work presents a flexible superconducting analogue-to-digital converter (ADC) architecture used to digitize low frequency signals with high dynamic range and quantum sensitivity. A new architecture of asynchronous mixed-signal HSQUID (Hybrid Superconducting QUantum Interference Device) is presented and studied experimentally in a Gifford-McMahon cryocooler at 4.2K. The analogue output of the asynchronous HSQUID allows the measurement of the signal change between digital switchings with an approximate sensitivity of 10 µΦ0/√Hz, with Φ0 being the quantization step of the asynchronous SQUID. The dynamics, the bias margins, as well as the influence of thermal noise are presented for this architecture based on two types of superconducting comparators. A study of INRiM's Superconductor-Normal metal-Insulator-Superconductor (SNIS) technology with self-shunted nano-junctions fabricated with the 3D Focused Ion Beam (FIB) technique was also carried out in order to design radio frequency nano-comparators with high energy efficiency.

Jury members :

• Mrs Claire ANTOINE - CEA SACLAY : Reviewer
• Mrs Annick DÉGARDIN - University Sorbonne : Reviewer
• Mrs Laurence MÉCHIN - CNRS : Examiner
• Mr Gilles MICOLAU - University Avignon : Examiner
• Mr Matteo FRETTO - INRIM : Examiner
• Mr Denis LE-JEUNE - ENSTA Bretagne : Examiner
• Mr Pascal FEBVRE - University Savoie Mont Blanc : Guest
• Mr Jean-Luc ISSLER - National Center for Space Studies : Guest