Decoherence of V$_{\rm B}^{-}$ spin defects in monoisotopic hexagonal boron nitride

Abstract

Spin defects in hexagonal boron nitride (hBN) are promising quantum systems for the design of flexible two-dimensional quantum sensing platforms. Here we rely on hBN crystals isotopically enriched with either 10 B or 11 B to investigate the isotope-dependent properties of a spin defect featuring a broadband photoluminescence signal in the near infrared. By analyzing the hyperfine structure of the spin defect while changing the boron isotope, we first unambiguously confirm that it corresponds to the negatively-charged boron-vacancy center (V − B ). We then show that its spin coherence properties are slightly improved in 10 B-enriched samples. This is supported by numerical simulations employing cluster correlation expansion methods, which reveal the importance of the hyperfine Fermi contact term for calculating the coherence time of point defects in hBN. Using crossrelaxation spectroscopy, we finally identify dark electron spin impurities as an additional source of decoherence. This work provides new insights into the properties of V − B spin defects, which are valuable for the future development of hBN-based quantum sensing foils.

Room temperature coherent control of protected qubit in hexagonal boron nitride

“…We note that the T echo is comparable to the T Rabi times. These findings are similar to those of Haykal et al (6), and in the high microwave-power regime our T echo = 100 ns is a close match to their calculations for a natural 20:80 mix of 10 B and 11 B isotopes. We note that data reported by Liu et al (29) is compatible with T echo of <100 ns under similar conditions.…”

“…Here, we present a study of the spin properties of ensembles of V − B in hBN. We confirm the findings of Haykal et al (6) that the majority of the spin echo coherence is lost in T echo < 100 ns at room temperature and milli-Tesla magnetic fields. However, we propose and demonstrate a solution.…”

“…So far, in hBN there have been claims of spin echo times in the µs-regime, at room temperature and moderate magnetic-field (13,19), which is competitive with NV-centers in small nano-diamonds (9). However, this has been challenged by experiments that show sub-100 ns spin echo times in isotopically purified material, which are further supported by calculations of the decoherence expected from the electron-nuclear interactions (6).…”

“…Firstly, some color-centers in hBN exhibit attractive quantum emission properties such as high brightness at visible wavelengths, well-matched to silicon detectors (2), and suggestions of transform-limited transitions with a high fraction of emission occurring through the zero-phonon line (3,4). ODMR provides a useful tool for identifying defects, that has been instrumental in identifying the boron vacancy in hBN (5,6). Secondly, if a defect could be identified that combines the excellent quantum emitter properties with a spin memory this could provide a competitive system to build a spin-photon interface (7).…”

Nuclear spin polarization and control in a van der Waals material

“…Nitrogen nuclear spins in the triangle lattice in hBN will be suitable for large-scale quantum simulation of different magnetic states [15], including spin liquids [11,12]. Their coherence time can be improved further by reducing the temperature and engineering isotope compositions [47,48].…”