Magnetic-field dependent VB- spin decoherence in hexagonal boron nitrides: A first-principles study

TL;DR

This study uses first-principles simulations to analyze how magnetic fields influence spin decoherence of VB- defects in hexagonal boron nitrides, revealing a transition in decoherence mechanisms and guiding qubit design.

Contribution

It provides the first detailed analysis of magnetic-field-dependent VB- decoherence in h-BN using ab initio methods, identifying a transition boundary and effects of isotopic variations.

Findings

Decoherence mechanism shifts at a specific magnetic field (transition boundary).

Larger nuclear spins extend the magnetic field range of decoherence effects.

Analytical models accurately predict the transition boundary and decoherence behavior.

Abstract

The negatively charged boron vacancy (VB-) in h-BN is a spin-1 defect functioning as an optically addressable spin qubit in two-dimensional materials. A precise understanding of its spin decoherence is essential to advance it into a robust qubit platform. First-principles quantum many-body simulations are employed to investigate VB- decoherence in dense nuclear spin baths of h-BN under magnetic fields from 0.01 to 3 T, considering isotopic variants h-10B14N, h-11B14N, h-10B15N, and h-11B15N. A transition boundary (TB) is observed where the dominant decoherence mechanism changes: below the TB, sub-microsecond decoherence is governed by independent nuclear spin dynamics, whereas above it, pairwise flip-flops dominate, extending T2 to tens of microseconds. Analytical predictions place the TB at 0.502 T for h-10B14N and 0.205 T for h-11B14N. The larger TB in h-10BN results from the larger nuclear spin of 10B (I = 3), which produces stronger nuclear modulation over a wider field range. The analytical approach also explains the magnetic-field-insensitive fast modulation observed below the TB. These findings clarify the role of dense nuclear spin baths with large nuclear spins (I >= 1) in VB- decoherence and provide design principles for isotopically engineered h-BN spin qubits.