Room Temperature Initialisation and Readout of Intrinsic Spin Defects in a Van der Waals Crystal (1906.03774v1)

Abstract: Optically addressable spins in widebandgap semiconductors have become one of the most prominent platforms for exploring fundamental quantum phenomena. While several candidates in 3D crystals including diamond and silicon carbide have been extensively studied, the identification of spindependent processes in atomically thin 2D materials has remained elusive. Although optically accessible spin states in hBN are theoretically predicted, they have not yet been observed experimentally. Here, employing rigorous electron paramagnetic resonance techniques and photoluminescence spectroscopy, we identify fluorescence lines in hexagonal boron nitride associated with a particular defect, the negatively charged boron vacancy and determine the parameters of its spin Hamiltonian. We show that the defect has a triplet ground state with a zero field splitting of 3.5 GHz and establish that the centre exhibits optically detected magnetic resonance at room temperature. We also demonstrate the spin polarization of this centre under optical pumping, which leads to optically induced population inversion of the spin ground state a prerequisite for coherent spin manipulation schemes. Our results constitute a leap forward in establishing two dimensional hBN as a prime platform for scalable quantum technologies, with extended potential for spin based quantum information and sensing applications, as our ODMR studies on hBN NV diamonds hybrid structures show.

• The paper demonstrates room-temperature initialization and optical readout of S=1 boron vacancy defects in hBN using photon-mediated spin polarization.
• It combines EPR and ODMR spectroscopy to characterize intrinsic spin properties, revealing a ZFS of ~3.5 GHz and an almost isotropic g-factor of 2.000.
• The findings indicate that hBN’s intrinsic spin defects hold promise for scalable quantum sensing and information processing in 2D materials.

Room Temperature Initialisation and Readout of Intrinsic Spin Defects in a Van der Waals Crystal

The paper investigates the photon-mediated spin polarization and readout processes in hexagonal boron nitride (hBN), a van der Waals (vdW) crystal, demonstrating the potential of hBN as a viable platform for scalable quantum technologies. This work not only identifies a specific defect within the hBN lattice—the negatively charged boron vacancy ($V_{\text{B}}^-$) with a spin triplet ground state—but also establishes its suitability for quantum information and sensing applications due to its remarkable room-temperature optical readout capabilities.

The paper effectively combines electron paramagnetic resonance (EPR) spectroscopy and optically detected magnetic resonance (ODMR) techniques to characterize the intrinsic defects in hBN, revealing the zero-field splitting (ZFS) and spin parameters of the boron vacancy defect. The defect exhibits a triplet state (S = 1) with a ZFS of approximately 3.5 GHz and an almost isotropic Landé factor of g = 2.000. A notable aspect of this research is the confirmation that these defects are self-contained within the structure and do not arise due to external inclusions, as demonstrated through various irradiation methods, such as ion-implantation and neutron irradiation.

The paper further elucidates the quantum emission characteristics of the boron vacancy, reinforcing the defect's stability and spin-photon interfacing potential. Detailed experiments concluded that under optical excitation, the spin states undergo population inversion, a prerequisite for coherent spin manipulation. These results bridge an essential gap between current 3D systems like diamond and 2D materials for advancing quantum technologies.

A substantial portion of the paper is devoted to the analysis of hyperfine interactions and the defect’s angular dependency through rigorous EPR and angular analysis of microwave-induced spin transitions. It establishes that the boron vacancy in hBN has a D3h point group symmetry, aligning with recent theoretical predictions indicating the stability of the $V_{\text{B}}^-$ defect with an S = 1 ground state. This symmetry and the spin characteristics allow seamless integration into optoelectronic devices and lend themselves to high-resolution quantum sensing due to nanoscale proximity and scalability afforded by 2D materials.

The research offers robust numerical evidence supporting the viability of hBN as a platform catering to quantum applications by demonstrating the intrinsic nature and optical readout capabilities of $V_{\text{B}}^-$ centers. The findings open up new prospects for developing advanced hBN-based hybrid structures for exploring coherent spin interactions and fostering scalable quantum devices.

This work implies potential directions for future research, including improved control over isotopic purity to further enhance coherent manipulation of spin states. The identified weaker interaction between defect electron spins and surrounding nuclear spins could potentially yield higher coherence times, beneficial for quantum information processing. The theoretical framework and advances in nanofabrication could expedite progress in spin-optomechanics, with hBN already showcasing promising nanophotonic traits.

In conclusion, this paper successfully establishes room-temperature initialization and readout mechanisms for S = 1 spin defects within hBN, marking a significant stride toward adopting 2D vdW materials for quantum technological applications. The integration of these findings could herald advancements in the quantum sensing capabilities of hBN heterostructures, facilitating innovations in quantum information science.