While conventional qubits remain as fragile as fine china, susceptible to environmental decoherence, topological qubits come naturally "armor-plated" with intrinsic fault tolerance. For decades, scientists have been seeking for suitable physical platforms for these robust quantum building blocks.
The field witnessed a breakthrough in 2013 when researchers from Tsinghua University first observed the quantum anomalous Hall effect (QAHE). Now, researchers are mining new treasures from this "quantum goldmine"—the fractional quantum anomalous Hall effect (FQAHE). As a new member of the quantum Hall family, FQAHE systems at specific high filling factors or under superconducting conditions may host Z 3 parafermions, enabling Fibonacci anyonic statistics and ultimately universal topological quantum computation.
A recent Science Bulletin News & Views article by Hai-Zhou Lu’s team at Southern University of Science and Technology provides commentary on this frontier. The review highlights twisted bilayer MoTe 2 and rhombohedral multilayer graphene/hBN moiré superlattices as promising material platforms for universal topological quantum computation, owing to their unique FQAHE signatures. The former exhibits pronounced FQAHE at -2/3 and -3/5 filling fractions, while the latter hosts more fractional states—including even-denominator fillings.
The team outlines two potential pathways toward Z 3 parafermions: (1) High-filling states (e.g., ν=13/5) could emulate the Read-Rezayi fractional quantum Hall state known to support Z 3 parafermions; (2) Coupling FQAHE with superconductivity may create fractional topological superconductors with Z 3 parafermion edge modes. Specifically, twisted MoTe 2 demonstrates high-filling fractional quantum spin Hall states and can be made superconducting via palladium metalization, while rhombohedral multilayer graphene shows high-Chern-number QAHE with possible intrinsic superconductivity.
Despite these advances, challenges remain in achieving the required high-filling states, stabilizing fractional topological superconductors, and improving material quality. Overcoming these hurdles will be crucial for transforming FQAHE systems into practical platforms for universal topological quantum computation.
Science Bulletin