Epitaxy of Advanced Nanowire Quantum Devices (1705.01480v3)

Abstract: Semiconductor nanowires provide an ideal platform for various low-dimensional quantum devices. In particular, topological phases of matter hosting non-Abelian quasi-particles can emerge when a semiconductor nanowire with strong spin-orbit coupling is brought in contact with a superconductor. To fully exploit the potential of non-Abelian anyons for topological quantum computing, they need to be exchanged in a well-controlled braiding operation. Essential hardware for braiding is a network of single-crystalline nanowires coupled to superconducting islands. Here, we demonstrate a technique for generic bottom-up synthesis of complex quantum devices with a special focus on nanowire networks having a predefined number of superconducting islands. Structural analysis confirms the high crystalline quality of the nanowire junctions, as well as an epitaxial superconductor-semiconductor interface. Quantum transport measurements of nanowire "hashtags" reveal Aharonov-Bohm and weak-antilocalization effects, indicating a phase coherent system with strong spin-orbit coupling. In addition, a proximity-induced hard superconducting gap is demonstrated in these hybrid superconductor-semiconductor nanowires, highlighting the successful materials development necessary for a first braiding experiment. Our approach opens new avenues for the realization of epitaxial 3-dimensional quantum device architectures.

• The paper introduces a scalable epitaxial approach for constructing single-crystalline InSb nanowire networks with precisely defined superconducting islands.
• It demonstrates robust phase coherence through Aharonov-Bohm oscillations and confirms a hard superconducting gap via high-resolution microscopy.
• The research paves the way for Majorana braiding operations in topological quantum computing, showing device performance up to 1.6 K and 0.9 T.

Overview of "Epitaxy of Advanced Nanowire Quantum Devices"

The paper "Epitaxy of Advanced Nanowire Quantum Devices" presents a comprehensive investigation into the fabrication and electronic characterization of semiconductor nanowire networks for quantum applications. The research primarily focuses on bottom-up synthesis techniques for constructing high-quality InSb nanowire networks, which are pivotal for achieving the Majorana Zero Modes (MZMs) essential for topological quantum computing.

Key Contributions

The authors have made significant advancements in the controlled epitaxial growth of nanowire networks with predefined superconducting islands using InSb nanowires interfaced with superconductors. These devices exhibit high crystalline integrity and form a crucial foundation for future quantum computing technologies. The research addresses major challenges such as achieving a hard superconducting gap and phase coherence, necessary for Majorana braiding operations.

1. Nanowire Network Synthesis: The paper introduces a novel approach for constructing single-crystalline InSb nanowire networks with precise control over the number and arrangement of superconducting islands. This is achieved through careful fabrication steps on an engineered substrate with trench-defined growth sites, utilizing electron-beam lithography (EBL) and catalyst deposition techniques.
2. Structural and Electronic Analysis: High-resolution techniques, such as STEM and HRTEM, confirm the high crystalline quality and epitaxial interface of the synthesized nanowires. Moreover, device measurements demonstrate phase coherent transport phenomena and the presence of a hard superconducting gap, affirmed by Aharonov-Bohm oscillations and weak-antilocalization effects.
3. Scalable Fabrication Process: The fabrication process minimizes crystal lattice mismatches and optimizes the yield of crossed junctions, crucial for scalable quantum architectures. The integration of semiconductors with superconductors is achieved without additional etching, preserving device performance.

Experimental Results

• Phase Coherence and Spin-Orbit Coupling: The "hashtag" nanowire networks showed clear Aharonov-Bohm oscillations with a phase coherence length of approximately 2.3 ± 0.3 µm at 300 mK, indicating robust phase coherence. A strong spin-orbit coupling is evidenced by the observation of weak-antilocalization peaks.
• Induced Hard Superconducting Gap: The research successfully demonstrates an induced superconducting gap with a sub-gap conductance ratio (G /G ) of ~100, showcasing the high quality of the superconductor-semiconductor interface critical for Majorana modes.
• Temperature and Magnetic Field Dependence: The persistence of Aharonov-Bohm oscillations up to ~1.6 K and the superconducting gap enduring magnetic fields up to B ~ 0.9 T underscore the thermal and magnetic robustness of the fabricated devices, which surpasses the threshold required for achieving the topological phase transition in InSb.

Implications and Future Directions

This paper directly impacts the future development of quantum devices by providing a pathway to achieve high-quality nanowire junctions suitable for implementing topological quantum computations. The demonstrated material advances pave the way for experimental verification of Majorana braiding, a milestone toward scalable quantum computing systems. Furthermore, the generic nature of the platform opens avenues for alternative superconductor-semiconductor combinations, offering broad applicability in quantum device architectures.

In conclusion, the paper provides a substantial contribution to the field of quantum device fabrication, specifically in exploiting semiconductor nanowires for topological quantum computing. The approaches and findings documented could significantly enhance the development trajectory of quantum computing technologies, propelling further research into robust quantum systems with operational feasibility at reasonable temperatures and magnetic fields.