Photodynamics and Temperature Dependence of Single Spin Defects in Hexagonal Boron Nitride Reveal Cascading Spin Transitions and Enhanced Coherence at Reduced Temperatures
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Single spin defects within hexagonal boron nitride currently attract considerable attention as promising building blocks for future quantum technologies, but a detailed understanding of how these defects behave remains elusive. Benjamin Whitefield, Ivan Zhigulin, and Nicholas P. Sloane, from the University of Technology Sydney, alongside Jean-Philippe Tetienne from RMIT University and Igor Aharonovich and Mehran Kianinia from the University of Technology Sydney, now present a comprehensive investigation into the photodynamics and temperature dependence of these defects. Their work reveals that spin transitions occur within a metastable energy landscape, following a cascading rate model, and demonstrates that both spin-lattice relaxation and coherence times improve at lower temperatures. Significantly, the team finds that the optical frequencies of these defects remain remarkably stable across a range of cryogenic temperatures, establishing their potential as robust and reliable quantum sensors. HBN Defects and Their Quantum Spin Properties Quantum emitters in hexagonal boron nitride (hBN) exhibiting optically detected magnetic resonance (ODMR) signatures are attracting significant attention as a promising solid-state platform for quantum technologies. This work investigates the underlying spin dynamics and mechanisms determining the origin of these spin-active emitters, aiming to establish a fundamental understanding of their spin properties and potential for quantum information processing. The research focuses on identifying the atomic structure of the defects responsible for the ODMR signals, and characterizing their spin coherence times and interactions with the surrounding hBN lattice. Through a combination of advanced optical spectroscopy, including ODMR measurements at cryogenic temperatures, and theoretical modelling, the team unravels the complex interplay between defect structure, spin dynamics, and optical properties. This approach allows for detailed analysis of the energy levels, g-factors, and hyperfine interactions associated with the spin-active defects, providing crucial insights into their potential as qubits.
Charge Transfer Creates Stable Spin Pairs This research details the investigation of optically addressable spin defects in hexagonal boron nitride (hBN), focusing on a novel mechanism involving charge transfer between neighboring defects to create robust and controllable spin pairs. The core discovery is that the observed spin properties originate not from single defects, but from pairs where one defect acts as a charge reservoir and the other as a spin-active center. Optical excitation triggers charge transfer, creating a stable spin state. This charge transfer mechanism explains the observed long coherence times and optical addressability of these spin defects, even at room temperature. The spin pairs consist of a donor-acceptor configuration, where one defect readily accepts or donates electrons, while the other hosts the spin. Excitation with light initializes the spin state of the acceptor defect, allowing for optical readout and control. The charge transfer stabilizes the spin state, protecting it from decoherence caused by environmental noise, resulting in significantly longer coherence times compared to isolated defects. This mechanism isn’t limited to a specific type of defect and can potentially be realized with various combinations of defects in hBN and other 2D materials. These spin pairs hold potential for quantum sensing, detecting weak magnetic fields, temperature, pressure, and other physical quantities, as well as for quantum information processing and nanoscale magnetometry.
This research provides a crucial understanding of the origin of robust spin properties in hBN, opening up new avenues for engineering and controlling spin defects in 2D materials. Spin States and Single Photon Emission in hBN This work presents a detailed investigation of spin complexes within hexagonal boron nitride (hBN), revealing crucial insights into their spin dynamics and potential for solid-state technologies. Researchers successfully characterized these defects, identifying two distinct spin states arising from charge transfer between nearby defects: a strongly coupled S = 1 manifold and a weakly coupled regime with S = {0,1}. Photoluminescence spectroscopy revealed a zero phonon line centered at approximately 720nm, with second order autocorrelation demonstrating single photon emission. Detailed ODMR spectroscopy identified specific transitions within the spin complex. The -1⁄2 ↔ +1⁄2 transition occurred at 1. 9GHz, while the 0 ↔ -1 and 0 ↔ +1 transitions were observed at 1 and 2. 7GHz respectively, all measured under a 68 mT magnetic field. Time-resolved photoluminescence decay measurements demonstrated a characteristic lifetime of 2. 5ns, consistent with other hBN quantum emitters. Pulsed ODMR measurements were then employed to analyze the internal electron transition rates. Rabi oscillations were driven on both the 0 ↔ +1 and -1⁄2 ↔ +1⁄2 spin transitions, exhibiting π-pulse durations of 42 and 87ns respectively. Importantly, the oscillations revealed distinct damping rates and an increasing envelope amplitude, indicating a long spin dependent recovery process originating from metastable states. Fitting the oscillations revealed damping times of 147ns and 75ns for the 0 ↔ +1 and -1⁄2 ↔ +1⁄2 transitions respectively, and metastable state depopulation times of 190ns and 212ns. These findings demonstrate the presence of long-lived metastable states influencing the spin dynamics of these hBN defects and provide a foundation for their implementation in future quantum technologies.
Defect Spin Dynamics in Boron Nitride This research delivers new understanding of spin complexes within hexagonal boron nitride, materials increasingly investigated for quantum technologies. Scientists performed detailed studies of how these spin complexes behave when exposed to light and microwaves, revealing that transitions between spin states occur within a metastable, or temporarily stable, excited state. Analysis of these transitions confirms a cascading population process, where the system moves through a weakly coupled spin pair before returning to its ground state. Temperature-dependent measurements further illuminate the behaviour of these defects, demonstrating that both relaxation and coherence times increase as temperature decreases. Importantly, the frequency of the S=1 transition remains relatively stable across varying temperatures, suggesting potential for robust sensing applications at cryogenic temperatures. The research indicates that the weakly coupled spin pair is more sensitive to environmental changes than the S=1 transition, offering clues about the structure of these defects. These findings support existing models of spin-pair defects and provide valuable new insights into their fundamental properties, advancing the development of solid-state quantum technologies. 👉 More information 🗞 Photodynamics and Temperature Dependence of Single Spin Defects in Hexagonal Boron Nitride 🧠 ArXiv: https://arxiv.org/abs/2512.07067 Tags: