Superconducting and semiconducting hybrids and advance memory concepts for superconducting electronics

M. R. Beasley, Mannie Horowitz

The goal of this program is to explore advanced alternatives to the standard approaches to memory in Josephson junction digital electronics. The work includes the physics, circuits and systems aspects of the problem. It is widely recognized that memory is the weak suit of digital superconductive electronics. There are several problems. They are hard to build, particularly at high densities. Their speed is being challenged by leading edge semiconductor memories, albeit at the expense of high power dissipation. They are susceptible to trapped flux, which is both random in space and likely varying in time. All the current approaches to memory are based on the concept of storage of magnetic flux in a superconducting ring first proposed over 25 years ago by Anacker. Basically, there have been no new ideas in superconductive memory since that time.

Pascal Febvre

Hisao Hayakawa

M. R. Beasley, Horowitz

Superconducting logic circuits based on Josephson junctions (JJ) are the fastest, lowest power solid state digital circuit technology known. Large scale integration of such circuits has also been demonstrated. By contrast, current superconducting memory circuits based on flux quantization are not equivalently advanced. Very dense memory chips have not been possible to date and seem unlikely to come without new invention. The goal of this project was to explore alternative approaches to memory that would be compatible with Josephson junction logic circuits and capable of much denser memory arrays. Five new approaches were investigated ranging from modification to the current approach, use of semiconductor CMOS and wholly new concepts based on new physical principles. Three of these were identified as worth pursuing. They are use of cooled CMOS, use of cryogenic hybrid JJ/CMOS memory concepts and a totally new magnetoresistive approach to memory based on the superconductor/ferromagnet proximity effect.

Kaveh Delfanazari, Jiahui Li, Yusheng Xiong +11 more

A quantum point contact (QPC)—a constriction in a semiconducting two-dimensional electron system with a quantized conductance—is a building block of novel spintronic and topological electronic circuits. QPCs can also be used as readout electronics, charge sensors, or switches in quantum nanocircuits. A short and impurity-free constriction with superconducting contacts is a Cooper-pair QPC analogue known as a superconducting quantum point contact (SQPC). The technological development of such quantum devices has been prolonged due to the challenges of maintaining their geometrical requirement and near-unity superconductor-semiconductor interface transparency. Here, we develop advanced nanofabrication, material and device engineering techniques and report on an innovative realization of nanoscale hybrid SQPC arrays with split gate technology in semiconducting 2D electron systems. We exploit the special gate tunability of the quantum wells, and demonstrate the first experimental observation of conductance quantization in hybrid InGaAs-Nb SQPCs. We observe reproducible quantized conductance at zero magnetic fields in multiple quantum nanodevices fabricated in a single chip and systematically investigate the quantum transport of SQPCs at low and high magnetic fields for their potential applications in quantum metrology, for extremely accurate voltage standards, and fault-tolerant quantum technologies. Published by the American Physical Society 2024

Pascal Febvre