Akira Fujimaki

Nagoya University, Japan

A New Era of Superconductor Digital Electronics Ushered in by π Junctions

Abstract

The superconductor π-phase-shift magnetic Josephson junctions (π-JJs), invented in the 2000s, function as a complement to the conventional Josephson junction (0-JJ). When a superconducting loop including a π-JJ is formed, the energy spontaneously possessed by the π junction itself is distributed to other elements in the loop, such as inductances and 0-JJs, bringing new functions to various circuits that could not be imagined in the past. Such functions will overcome the issues left for practical use, opening a new era of superconductor digital electronics. The specific effect of the π-JJs appears as a spontaneous current resulting from the distribution of energy of the π-JJ. This current reduces the energy required for switching 0-JJs, enabling logic circuits whose power consumption is one order smaller than that of the single-flux-quantum (SFQ) circuit, while ultra-high-speed microprocessors based on the SFQ circuit have been demonstrated so far. In addition, π-JJ-based impulse-driven matrix memories can operate above 20 GHz because the memories are free from charging and discharging processes in cell selection. Furthermore, quantum annealing circuits can efficiently combine two physically separated qubits. In this presentation, I will report on the latest research and development of the above-mentioned π-JJ-based technologies.

Biography

Akira Fujimaki received his B.E., M.E., and Dr. Eng. Degrees from Tohoku University in 1982, 1984, and 1987, respectively. He was a visiting researcher at the University of California, Berkeley, in 1987. Since 1988, he has been working at the Graduate School of Engineering, Nagoya University, Japan, where he is currently a professor. Since 2019, he has also been a vice president of Nagoya University. He has been working on superconducting digital electronics since 1981. He observed various dynamic behaviors of fluxons in Josephson networks. He also demonstrated the single flux quantum circuits by using Nb-based Josephson junctions, and high-temperature-superconductor-based junctions. The circuits are applied to the software-defined radio receivers, the detector systems. Currently his research focuses on high-performance computers. His group developed the integration technology of π-phase-shifted magnetic Josephson junctions. Based on those, he has been tackling to develop energy-efficient logic circuit, matrix memories, and quantum annealing circuits.