Quantum Device Architecture for Robust Phase-Coherent Electron Transport in Topological Hinge States

Background

Topological insulators (TIs) represent a rapidly advancing field in condensed matter physics, distinguished by their unique electronic properties: while the bulk of these materials is insulating, their surfaces or edges can conduct electricity via special states protected by topological invariants. More recently, the concept of higher-order topological insulators (HOTIs) has emerged, where conduction is not just limited to surfaces but can be confined to even lower-dimensional boundaries, such as edges or hinges. These exotic states offer the promise of robust, dissipationless transport channels that are immune to certain types of disorder and defects, making them highly attractive for quantum electronic devices. The ability to exploit quantum coherence in these systems, particularly through phenomena like the Aharonov-Bohm effect, is seen as a crucial step toward realizing scalable, energy-efficient quantum technologies.

Despite their promise, current approaches to harnessing quantum coherent transport in topological materials face significant limitations. In conventional TIs, surface or edge conduction often competes with unwanted bulk conduction, especially at finite temperatures or in imperfectly synthesized materials, leading to reduced device performance and loss of quantum coherence. Attempts to observe quantum interference effects, such as Aharonov-Bohm oscillations, have typically required complex nanostructuring or ultra-clean samples, and even then, bulk or surface conduction paths can obscure the contribution from topological channels. Moreover, many candidate materials are sensitive to disorder, environmental degradation, or symmetry breaking, which can destroy the protected states and limit practical device applications. These challenges underscore the need for new material systems and device architectures that can provide robust, phase-coherent transport exclusively through topologically protected channels, while suppressing unwanted conduction and maintaining stability under realistic operating conditions.

Technology

This technology is a quantum electronic device based on atomically thin, even-layered flakes of α-Bi₄Br₄, a higher-order topological insulator (HOTI). In this structure, the bulk and surfaces are insulating, but the edges—specifically, the hinges—host robust, gapless conducting states. The device is engineered so that these hinge states form a closed loop, enabling phase-coherent electron transport. When the phase coherence length of electrons exceeds the loop’s perimeter, the device exhibits clear Aharonov-Bohm oscillations in magnetoresistance, a signature of quantum interference. The fabrication process involves mechanical exfoliation of α-Bi₄Br₄ crystals, careful layer selection, and encapsulation to preserve integrity, followed by low-temperature transport measurements that confirm the presence and resilience of hinge conduction channels.

What differentiates this technology is its demonstration of quantum coherent transport exclusively through topologically protected hinge states in a truly insulating material. Unlike previous systems—where conduction often occurs through bulk or surface states, or requires complex nanostructuring—this approach leverages the intrinsic properties of HOTIs to achieve nearly non-dissipative, disorder-immune conduction in a scalable, flake-based geometry. The hinge states are robust against non-magnetic disorder and inversion symmetry breaking, ensuring stable operation even under practical conditions. This unique combination of topological protection, phase coherence at relatively high temperatures, and straightforward device architecture positions the technology as a promising platform for quantum interconnects, energy-efficient electronics, and future quantum information or spintronic applications.

Benefits

• Robust quantum coherent electron transport confined to topological hinge states
• Immunity to non-magnetic disorder and inversion symmetry breaking, ensuring stable device operation
• Low-dissipation conduction enabling energy-efficient quantum electronic devices
• Phase coherence length exceeding device perimeter, supporting strong quantum interference effects (Aharonov-Bohm oscillations)
• Scalable device architecture using atomically thin flakes suitable for integration into quantum circuits
• Potential applications in quantum information processing and spintronics due to spin-momentum locking and topological protection
• Experimental demonstration of quantum transport in an insulating higher-order topological insulator, minimizing bulk conduction issues

Applications

• Quantum interconnects for quantum computers
• Low-dissipation topological electronic circuits
• Robust spintronic device platforms
• Phase-coherent quantum sensors

Additional info

This quantum device utilizes even-numbered layers of $\alpha$-Bi₄Br₄, a higher-order topological insulator with insulating bulk and surfaces. Gapless hinge states form a singly connected loop, enabling phase-coherent electron transport. By maintaining coherence lengths exceeding the loop perimeter, the system exhibits Aharonov-Bohm oscillations. This configuration ensures stable, low-dissipation conduction confined to topological hinges, remaining resilient against non-magnetic disorder and inversion symmetry breaking.