## Dongxia Qu | 19-LW-040

### Project Overview

Over the last few decades, scientists have been attempting to create quantum coherent devices that are needed for a new generation of quantum computers. The main challenge in developing quantum computers is the high sensitivity of the quantum systems to the external environment, which destroys quantum states. One promising option is to use topologically protected Majorana bound states that are resistant to most local sources of decoherence. Majorana bound states are predicted to arise in a topological superconductor. So far, topological superconductivity has only been observed in a limited number of material systems, most of which are realized using complicated fabrication processes and at very low temperatures.

Topological superconductors promise an avenue towards quantum computation with an unprecedented low error rate. Our project provided an approach to creating and characterizing topological superconductors without fabricating a Josephson junction. We explored, for the first time, the possibility of generating topological superconductivity in a superconductor-island-array/topological insulator heterostructure fabricated using the focused ion beam technique. We demonstrated that such a heterostructure behaves as a dynamic Josephson junction, showing a Fraunhofer-like pattern of the critical current versus the applied magnetic field. Our measurements suggest that topological superconductivity can be induced in a hybrid superconducting nanoislands/topological insulator heterostructure. Our work provides both a pathfinder for inducing topological superconductivity in a three-dimensional topological insulator and an innovative approach that can be extended to other materials to generate and characterize topological superconductors.

### Mission Impact

Our research supports Lawrence Livermore National Laboratory's mission research challenge in quantum science and technology, as well as the Department of Energy's goal to develop controllable and scalable quantum hardware devices and systems. In addition, this project advanced our ability to understand and ultimately synthesize topological superconductors in pursuit of topological quantum computation, which contributes to the Laboratory's core competency in advanced materials and manufacturing, including superconducting quantum systems.