Decoherence time of the ground state spin of $V_{B}$ centers in hexagonal boron nitride

Abstract: The ground-state spin of optically active defects in hexagonal boron nitride (hBN) offers a promising platform for quantum information applications, such as qubits for quantum computing and nanoscale sensing. A key characteristic of a qubit is its decoherence time, as its duration and controllability are critical for practical applications in quantum technologies. In this work, we investigate the electron spin dephasing time of the negatively charged boron vacancies, $V_{B}$ centers, in the hBN lattice by considering the dipolar hyperfine as well as spin-phonon interactions. We employ an approximate method based on the Holstein-Primakoff transformation to take into account a large number of nuclear spins and Debye model to consider the effect of lattice phonons. We show that, in the presence of the dipolar hyperfine interactions, Hahn-echo coherence time of the $V_{B}$ electron spin is approximately $30: \mathrm{\mu s}$ at room temperature. Our results provide a step forward in understanding the $V_{B}$ defect decoherence in the hBN, which might be used for quantum information applications.