The interplay between superconductivity and quantum Hall effect has recently been demonstrated in graphene-based devices, revealing intriguing possibilities for new quantum phases[1,2]. However, graphene requires large magnetic fields (~8T) for the quantum Hall effect to fully develop, severely limiting the parameter space where superconductivity can survive. This project aims to investigate this rich physics using germanium quantum wells [3] - a uniquely promising platform where the quantum Hall effect emerges at remarkably low magnetic fields of around 1 Tesla, offering unprecedented opportunities for quantum computing applications.
Research Goals
This DPhil project at Oxford's Department of Materials will focus on two key research directions:
1. Topological Josephson Junctions in Germanium Quantum Wells:
- Engineer and characterize Josephson junctions in the quantum Hall regime
- Develop microwave spectroscopy techniques to probe the nature of bound states at the superconductor-quantum Hall interface
- Investigate the potential of these states for topologically protected qubits operating at accessible magnetic fields
2. Novel Qubit Architectures Exploiting Low-Field Quantum Hall States:
- Design and implement new types of quantum devices that leverage the unique low-field regime of germanium
- Study coherence properties of quantum states emerging at the interface between superconductivity and quantum Hall effect
- Explore ways to control and manipulate these states for quantum information processing
- Work towards demonstration of basic braiding operations as building blocks for topological quantum computation
The work combines advanced device fabrication with sophisticated quantum measurements:
- Development of high-mobility germanium quantum wells with superconducting contacts
- Implementation of high-frequency measurement techniques for qubit characterization
- Design and fabrication of interferometric devices for quantum state manipulation
- Low-temperature transport measurements in the quantum Hall regime
The successful candidate will gain expertise in:
- Device fabrication
- Advanced measurement techniques
- Data acquisition and processing
This work is particularly timely as the quantum computing community seeks new platforms for robust qubits. The unique properties of germanium quantum wells - especially the ability to reach the quantum Hall regime at low magnetic fields - may provide crucial advantages for developing protected quantum bits operating in parameter regimes more compatible with existing superconducting quantum computing architectures.
[1] Barrier, Julien, et al. "One-dimensional proximity superconductivity in the quantum Hall regime." Nature 628.8009 (2024): 741-745.
[2] Vignaud, Hadrien, et al. "Evidence for chiral supercurrent in quantum Hall Josephson junctions." Nature 624.7992 (2023): 545-550.
[3] Myronov, Maksym, et al. "Holes outperform electrons in group IV semiconductor materials." Small Science 3.4 (2023): 2200094.
