EAGER: BRAIDING: Materials to enable voltage-gateable Majorana systems in silicon using top-down fabrication techniques

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Non-technical Abstract: Modern state of the art single-chip processors that go into our everyday electronic devices, such as cellphones, contain billions of transistors. This number has been doubling ever since 1971 approximately every two years following the trend of Moore's law. We are now at the threshold of ultimate capacity, which motivates the search for new integrated circuits. This EAGER project is for novel exploratory work whose eventual goal is to create and manipulate silicon-based superconducting heterostructures in order to provide a foundation for topological quantum transistors. This project builds on recent experimental progress demonstrating that superconductivity arises in doped covalent semiconductors, and the use of Si is attractive because this material is the most common semiconductor in the modern microelectronics industry. It is therefore motivating to explore an approach where highly scalable gate control of semiconductors can be incorporated into superconducting devices for quantum computing purposes. This could be achieved by defining superconducting-semiconductor quantum circuits using metal top gates, a technology similar to that currently employed in large scale microelectronics. Under certain conditions these circuits have very special properties encoded by Majorana modes, which are excitations that enable operations that are protected by topological principles. Thus, these systems are potentially highly resistant to various sources of decoherence, which is the main problem in non-topological quantum processors. Implementing topological quantum computation is a grand challenge with potentially transformative societal implications. The work on the project will have an impact on development of human resources by training of graduate students and other junior scientists in quantum information, nanofabrication, characterization of qubits and materials, theoretical simulation and calculation, and experimental design and practice. Technical Abstract: This EAGER project is for novel work to explore an approach where highly scalable gate control of semiconductors can be incorporated into superconducting devices for quantum computing purposes. The proposed research aims to characterize and develop superconducting semiconductor quantum circuits supporting Majorana fermion states using metal top gates, a technology similar to that currently employed in large-scale microelectronics. The project is balanced between the experiment and theory in the Physics Department of the University of Wisconsin-Madison. Experimental goals include: (i) development of lithographically patternable and voltage-gateable superconducting layers in silicon enriched by gallium; (ii) realization of all-silicon superconducting semiconductor Josephson field effect transistors; (iii) measurements of various transport characteristics of Josephson junctions such as current voltage characteristics, current-phase relationships, and Fraunhofer interference patterns. Theoretical efforts include exploration of patternable micromagnet configurations within the superconducting silicon channel that enable formation of robust Majorana modes. Theory work additionally includes computation of essential parameters for the silicon-gallium superconductor in the presence of doping-induced inhomogeneities, modeling transport characteristics of proposed devices, and determination of the phase diagram that hosts topologically nontrivial states in terms of realistic parameters that are controllable experimentally.