A Pair of Pioneering Quantum Devices: Catching up with the Pribiag Group

Pribiag’s group published an article in the October Issue of Nano Letters about finding evidence for π-Shifted Cooper Quartets and Few-Mode Transport in PbTe Nanowire Three-Terminal Josephson Junctions. Pribiag’s group demonstrated the first successful few mode three terminal Josephson junction three years ago and has been working to unlock new physics with this experimental technique. According to Pribiag, hybrid superconductor–semiconductor Josephson devices offer a promising path to engineering tunable quantum matter, which is an important step toward building quantum simulators. These simulators combine predictable quantum correlations and coherence via the superconductor component with precise local electrostatic control, owing to their simultaneous semiconducting character.

The Josephson effect happens when two (or more) superconductors are placed in close proximity to one another with some barrier between them. In typical superconductors, two electrons become bound together at low temperatures. These electrons are called Cooper pairs.  In the multi-terminal Josephson junction, two Cooper pairs can become correlated, forming a state known as Cooper quartets. This can lead to multiple superconductors becoming coupled phase-coherently with one another, which is a requirement for realizing certain proposals for tunable artificial quantum matter. To achieve this multi-terminal coupling, the Pribiag group used specially-designed semiconductor nanowires with three prongs, grown by collaborators in the Erik Bakkers group at T. U. Eindhoven. This specific nanowire geometry allows the superconductors to connect in a small common region of space, which preserves phase-coherence and allows electrostatic gate control of the superconductivity.   

The members of Pribiag’s group that worked on the research and paper are Mohit Gupta, Vipin Khade, Colin Riggert, Lior Shani and Gavin Menning. 

The second article appeared in Science Advances in late March, detailing an effort to create a deterministically-positioned three dimensional electronic device, using nature as inspiration and as a core building block.  A three dimensional architecture would allow for a much greater density of information for a quantum device. Two dimensional nanoscale devices are typically created by patterning materials with the aid of nanolithographic processes, a top down approach used in research and industry. Creating a three dimensional structure with this process has met serious technical roadblocks. To work around this, the physicists turned to DNA strands for help in building a bottom up nanometer structure, but in the past this approach resulted in randomly-dispersed structures, which could not be used for a large-scale device fabrication. To address this, collaborators in the Oleg Gang group at Columbia University and Brookhaven National Laboratory created a prototype device using an array of small gold squares as the base of a lattice, onto which short strands of DNA were spliced. The gold arrays allowed the physicists to grow a 3D DNA scaffolding in the desired locations on the chip, with high reproducibility. The team then converted these DNA scaffolds with silicon oxide laced with the semiconductor tin oxide, and connected metallic electrodes to each structure. The result — 3D photosensitive devices that respond electrically when illuminated.

This successful prototype will allow engineers to incorporate self-assembled DNA nanostructures into silicon wafers in a precise and deterministic manner, compatible with scalability requirements. Vlad Pribiag and Lior Shani from the School of Physics and Astronomy worked on the project. This research was sponsored by the W. M. Keck Foundation, a charitable foundation supporting scientific engineering and medical research in the United States since 1954, through a joint University of Minnesota-Columbia University effort led by Pribiag.