Breakthrough in Carbon-Based Quantum Materials at NUS

Researchers at the National University of Singapore (NUS) have unveiled a groundbreaking innovation in quantum materials science: Janus graphene nanoribbons (JGNRs). This development, detailed in a January 2025 Nature publication, promises to propel advancements in quantum computing and spintronics. Led by Associate Professor Lu Jiong from the NUS Department of Chemistry, the team engineered these novel structures with a unique asymmetric design, enabling the first one-dimensional ferromagnetic carbon chain.

The significance of this work lies in its potential to create stable, room-temperature operable spin qubits, addressing key challenges in scaling quantum technologies. As Singapore positions itself as a global quantum hub, NUS's contribution underscores the nation's growing prowess in higher education-driven research.

Understanding Graphene Nanoribbons: Foundations of the Innovation

Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene, a single layer of carbon atoms arranged in a honeycomb lattice, typically less than 10 nanometers wide. Discovered in 2004, graphene's exceptional properties—such as high electron mobility, mechanical strength, and thermal conductivity—make it a cornerstone for next-generation electronics. When sliced into nanoribbons, quantum confinement effects emerge, altering their electronic band structure based on edge type: armchair or zigzag.

Zigzag-edged GNRs (ZGNRs) are particularly intriguing due to unpaired π-electrons at the edges, leading to magnetic phenomena like antiferromagnetic coupling in symmetric designs. However, achieving isolated ferromagnetic states has been elusive until now. NUS's JGNRs break this barrier by introducing asymmetry, drawing inspiration from Janus materials—those with distinct properties on opposing sides, named after the two-faced Roman god.

The Unique Design of Janus Graphene Nanoribbons

JGNRs feature one pristine zigzag edge hosting localized ferromagnetic states and an opposing 'defective' edge modified with periodic benzene motifs. This topological defect array, guided by Lieb's theorem on sublattice imbalance and spin symmetry breaking, quenches magnetism on the modified side while concentrating it on the pristine edge. Two variants—(4,2)-JGNR and (5,2)-JGNR—were fabricated, with the parameter m denoting defect periodicity, tunable for customized properties.

Assoc Prof Lu Jiong explains: "Magnetic graphene nanoribbons offer tremendous potential for quantum technologies due to their long spin coherence times and room-temperature operation. Creating a single zigzag edge is daunting but essential for assembling multiple spin qubits." This design realizes the world's first 1D ferromagnetic carbon chain, verified through density functional theory (DFT) simulations showing ferromagnetic ground states.

On-Surface Synthesis: Precision Engineering at Atomic Scale

The synthesis begins with designing Z-shaped molecular precursors via solution-phase chemistry. These precursors are deposited on a gold (Au(111)) surface in an ultra-high vacuum chamber. Step-by-step:

1. Deposition and polymerization: Precursors align and covalently bond at 200°C, forming polymer chains.
2. Cyclization: Heating to 350°C aromatizes rings, yielding the GNR backbone.
3. Defect formation: Further annealing at 400°C introduces benzene motifs on one edge, creating the Janus asymmetry.

Scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) provided atomic-resolution images, while dI/dV spectroscopy mapped edge states. DFT corroborated experimental findings, confirming spin-polarized channels with tunable bandgaps.

Photo by Mari Ganesh Kumar on Unsplash

Experimental Verification and Theoretical Insights

High-resolution imaging revealed the precise atomic structure, with ferromagnetic states localized exclusively on the pristine zigzag edge—absent on the defective side. Bias-dependent spectroscopy showed metallic conduction along the spin chain, ideal for quantum transport. Collaborators like Prof Steven G Louie (UC Berkeley) and Prof Hiroshi Sakaguchi (Kyoto University) contributed theoretical modeling, predicting scalability to multi-qubit arrays.

This marks a leap from symmetric ZGNRs, where antiferromagnetic coupling limited utility. JGNRs' stability on Au(111) hints at transferability to other substrates for device integration.

Revolutionizing Quantum Computing with JGNRs

Quantum computing relies on qubits maintaining coherence against decoherence. Traditional superconducting qubits require cryogenic cooling; JGNRs offer carbon-based alternatives operable near room temperature with long coherence times. The 1D ferromagnetic chain acts as a robust spin qubit array, enabling bottom-up assembly for scalable quantum processors.

In spintronics—electronics harnessing electron spin—JGNRs provide tunable spin-polarized channels, potentially outperforming silicon in energy efficiency. For Singapore, this aligns with the National Quantum Strategy, investing S$37 billion by 2030 in quantum R&D.Singapore's quantum push positions NUS at the forefront.

Singapore's Quantum Ecosystem and NUS Leadership

Singapore's Centre for Quantum Technologies (CQT) at NUS drives quantum research, partnering with IBM (IBM-NUS Centre, 2025) and Quantinuum (Helios quantum computer arriving 2026). The National Quantum Office fosters talent, with JGNRs complementing photonic and trapped-ion efforts.

NUS's graphene expertise, including prior 'butterfly' nanographenes, builds a nanomaterials pipeline. International collaborations enhance global impact, attracting top researchers to Singapore's universities.

Challenges, Future Directions, and Career Opportunities

Challenges include ambient stability and large-scale production. Future work: varying m for magnetism tuning, spin resonance studies, device prototyping. Assoc Prof Lu envisions JGNRs enabling carbon spintronics at 1D limits.

For aspiring researchers, NUS offers PhD programs in quantum materials via CQT. Singapore's ecosystem provides industry linkages, fostering careers in quantum tech.

Photo by Danist Soh on Unsplash

• Benefits: Room-temp qubits reduce cooling costs by 90% vs. superconductors.
• Risks: Edge defects could introduce scattering; mitigated by precise synthesis.
• Comparisons: Superior to transition-metal dichalcogenides in carbon purity.

Stakeholder Perspectives and Global Implications

Prof Louie notes JGNRs' tunability from antiferro- to ferromagnetism. Sakaguchi highlights precursor design challenges. Industry views JGNRs accelerating quantum advantage, with market projected at US$10B by 2030.

Singapore's balanced ecosystem—universities like NUS, NTU, government funding—exemplifies higher education's role in innovation. This positions local colleges as hubs for quantum talent development.

Outlook: Singapore Leading Quantum Materials Revolution

JGNRs exemplify NUS's transformative research, blending chemistry, physics, and engineering. As quantum computing matures, expect JGNR-based prototypes by 2028, bolstering Singapore's tech sovereignty. For students and faculty, opportunities abound in this vibrant field.