Background

Superconducting electronics are attracting renewed interest as a platform for ultra-energy-efficient information processing. Recent developments include superconducting digital logic, adiabatic and reversible computing, oscillator-based computing, neuromorphic circuits, and other forms of unconventional computing. In most existing approaches, however, the nonlinear circuit functionality is fixed during fabrication through predefined Josephson junction parameters.

In parallel, gate-tunable Josephson junctions, often referred to as JoFETs, have emerged as a new class of superconducting devices in which the critical current can be controlled electrostatically. So far, these devices have mainly been studied in the context of mesoscopic superconductivity, hybrid quantum devices, and superconducting qubits.

This project explores a di6erent question: can sparse integration of gate-programmable Josephson elements into otherwise conventional superconducting circuits enable new nonlinear dynamical behaviour and new computational functionality?

Scientific Motivation

The aim is not to replace established Josephson circuit technology. Instead, the project investigates architectures in which a small number of gate-programmable Josephson elements are embedded at strategically selected locations within otherwise conventional superconducting circuits.

This approach combines the maturity, reproducibility, and scalability of established superconducting circuit technology with the additional flexibility of post-fabrication electrostatic programmability. The central hypothesis is that sparse programmability may provide access to nonlinear dynamical regimes that are difficult, inefficient, or impossible to realize using fixed Josephson circuits alone.

Possible directions include tunable nonlinear response, excitability and threshold dynamics, oscillator synchronization, reservoir-like behaviour, and reconfigurable superconducting circuit elements for unconventional computing architectures.

Objectives

The student will:

  • review the state of the art in superconducting unconventional computing, including adiabatic logic, reversible logic, neuromorphic circuits, reservoir computing, and oscillator networks;
  • connect superconducting circuit functions to computing operations needed in neuromorphic paradigms, such as Hodgkin–Huxley or FitzHugh–Nagumo behaviors, and/or tunable nonlinear functions used, for example, in Kolmogorov-Arnold networks (KAN);
  • investigate which superconducting circuit functions could benefit from sparse gateprogrammable Josephson elements;
  • develop simplified circuit models for selected candidate architectures;
  • identify experimentally feasible proof-of-principle circuits for possible future implementation.

Student Profile

We are looking for a highly motivated MSc student with a background in electronic device physics, superconducting circuits, nonlinear dynamics, or closely related fields. The project is well suited for a student with a strong interest in applied modelling, circuit design, and the physics of nonlinear electronic devices.

Since the project involves several departments, the student should be able to work independently and flexibly, while maintaining clear communication with supervisors from different research groups.

Your Task

The main task is to create and test a superconducting contact, using the state-of-the-art nanofabrication tools in the Helmholtz Nano Facility of FZ Jülich, and the cryogenic electronic measurement facilities in our cryolabs at the Peter Grünberg Institute of FZ Jülich. GeSn materials will be provided by the team of Dr. Dan Bucca. We envision trialing diffusion based superconducting contacts (e.g. realize creation of superconducting Platinum-Germanide PtGe2), as well as using reactive ion etching to etch down to the quantum well and seek contact with established superconductors such as Aluminum, Titanium, Niobium Titanium Nitride.

What we offer

  • Supervision by experts in gate-tunable Josephson devices and JoFET operation: Dr. Vincent Mourik, PGI-11
  • Supervision by experts in n superconducting circuit design and operation: Dr. Pavel Bushev, PGI-13
  • Supervision by experts in in neuromorphic computing and unconventional computing concepts: Prof. Dr. John Paul Strachan, PGI-14
  • Integration into the teams of Dr. Mourik, Dr. Bushev, and Prof. Dr. Strachan
  • Workplace access at Campus Boulevard 79, Campus Melaten, Aachen, and at PGI-14 Forschungszentrum Jülich, with the exact workplace arrangement to be confirmed
  • A laptop

Supervision

  • Dr. Vincent Mourik, FZ Jülich, PGI-11 [email protected]
    • Core expertise: Josephson junction characterization, Ge-based nanofabrication
  • Dr. Pavel Bushev, FZ Jülich, PGI-13 [email protected]
    • Core expertise: Josephson junction characterization, nanofabrication
  • Prof Dr. John Paul Strachan, FZ Jülich, PGI-14, [email protected]
    • Core expertise: GeSn heterostructure development, material characterization