Learning a van der Waals Qubit for Quantum Sensing and Noise Spectroscopy

Quantum sensors are an important emerging technology with wide wide-ranging use and the precision to outperform classical sensors for certain applications. While nitrogen-vacancy (NV) centers in diamond have demonstrated remarkable promise, van der Waals materials are emerging as prime candidates for next-generation quantum sensing. These materials are particularly attractive due to their atomically thin nature, defect-free surfaces, and potential for integration into hybrid systems. Among them, negatively charged boron vacancies in hexagonal boron nitride (hBN) have garnered significant attention. Much like NV centers, the spin states of boron vacancies can be optically read out with high-fidelity via fluorescence under green light excitation.<br/><br/>In this work, we demonstrate that using isotopically modified hBN (B¹⁰, N¹⁵) we "learn" the qubit Hamiltonian through comprehensive tomography via external vector magnet control. This approach reveals microscopic details of orientation-dependent electron-nuclear hyperfine interactions, which can significantly alter the Optically Detected Magnetic Resonance (ODMR) spectrum as well as the qubit’s decoherence profile. Leveraging this external control, we demonstrate that the qubit can be configured to act as either a purely magnetic sensor or an electric/strain sensor.<br/><br/>By employing dynamical decoupling sequences, we extend the coherence time of the boron vacancy center to nearly 0.1 milliseconds–the longest reported for any 2D material to date–and estimate the resulting sensitivity in quantum sensing applications. Furthermore, we perform noise spectroscopy to gain insights into the origin of qubit decoherence in both magnetic and electric regimes, aiming to identify feasible improvements for future experiments.<br/><br/>Collectively, our findings underscore the potential of hBN-based spin qubits for advanced quantum sensing applications. These results not only highlight the current capabilities of hBN qubits but also pave the way for future research aimed at optimizing their performance in quantum sensors.