Professor Chris Palmstrøm at ECE Fall 2023 Colloquium
Superconductor/Semiconductor Heterostructures for Quantum Computing Applications
Superconductor/semiconductor heterostructures have theoretically been predicted to have unique applications in quantum information systems. Coupling superconductivity to near surface quantum wells (QW) and nanowires of high spin-orbit semiconductors have allowed the observation of zero bias peaks, which can be a signature of, but not proof of, Majorana Zero Modes, a key ingredient for topological quantum computing. Although the Majorana Zero Modes have not been experimentally confirmed, induced superconductivity is observed and paves the way for lithographically defined complex superconductor/semiconductor nanostructured networks necessary for quantum computing.
Our efforts have focused on developing high mobility of near surface quantum wells of the high spin-orbit semiconductors InAs, InSb and InAsySb1-y. Rather than just relying on post growth lithography and top down etching to form semiconductor nanostructures, we have also investigated the development of shadow superconductor growth on atomic hydrogen cleaned MOVPE-grown vapor-liquid-solid InSb nanostructures and in-vacuum chemical and molecular beam epitaxy selective area grown InAs nanostructures. We have identified Sn as an alternative for Al for use as superconductor contacts to InSb vapor-liquid-solid nanowires, demonstrating a hard superconducting gap, with superconductivity persisting in magnetic field up to 4 Tesla. Further, a small island of Sn-InSb exhibits the two-electron charging effect, a clear indication of a supercurrent.
Lateral superconductor/semiconductor/superconductor structures allow for selective control of conductance modes in planar lateral multi-terminal Josephson Junctions. Vertical superconductor/semiconductor/superconductor heterostructures have the potential for combining the capacitor and Josephson Junction in a superconducting transmon qubit device into a single device, a merged element transmon, resulting in orders of magnitude reduction in size.
In this presentation, my group’s progress in developing superconductor/semiconductor heterostructures for quantum computing applications will be presented. This will include progress in in-situ patterning and selective area growth, multi-terminal Josephson Junctions and the recent progress towards developing a Si fin based merged element transmon – the FinMET.