The team led by Prof. Hosung Seo systematically studied the magnetic-field–dependent behavior of spin decoherence in the negatively charged boron vacancy (V_B^⁻) defect of hexagonal boron nitride (h-BN) and proposed practical guidelines for extending the coherence time (T₂). The study shows that the decoherence mechanism undergoes a transition across distinct magnetic-field regimes and provides recommended magnetic field ranges together with their microscopic origins for quantum information applications.

As a next-generation 2D materials platform for quantum technologies, the V_B^⁻ defect in h-BN offers an optically addressable spin qubit operating at room temperature. However, its short T₂ time has been a critical bottleneck to practical applications, calling for both practical strategy and microscopic understanding to enhance coherence.

In this work, the researchers combined density functional theory calculations with the generalized cluster-correlation expansion (CCE) to quantitatively investigate the decoherence across a broad range of magnetic fields. The results show that the isotopic composition of boron and nitrogen markedly affects T₂, and that a critical magnetic field strength (called transition boundary) exists, above which T₂ increases by two orders of magnitude. The analysis also identifies distinct modulations in coherence at particular magnetic fields originating from specific nuclear spins in h-BN.

This study presents a unified theoretical framework for the distinctive decoherence physics of h-BN, characterized by a dense nuclear-spin bath with high-nuclear-spin isotopes. Building on this framework, we propose design guidelines for spin qubits in 2D materials based on isotopic engineering and magnetic-field control. These guidelines support the quantum-devices design and the optimization of sensing conditions for h-BN based quantum information technologies.

This research was supported by the National Research Foundation of Korea (NRF), by Creation of the Quantum Information Science R&D Ecosystem through the NRF, and the education and training program of the Quantum Information Research Support Center at SKKU, funded through the NRF. The excellence of this work was recognized with publication in the Advanced Functional Materials (Impact Factor: 19.0), a leading international journal in the field of Applied Physics, on Aug. 24, 2025.

※ Paper Title: Magnetic-Field Dependent V_B⁻ Spin Decoherence in Hexagonal Boron Nitrides: A First-Principles Study

※ Journal: Advanced Functional Materials

※ DOI: https://doi.org/10.1002/adfm.202511274

V_B^- spin decoherence as functions of magnetic fields and transition boundary for decoherence