Determination of the Dipole Orientation of Single Defects in Hexagonal Boron Nitride

Dipole orientation in solid-state single photon emitters plays an important role in applications such as quantum information devices integrated with nanophotonic components. In various single photon emitters, hexagonal boron nitride (hBN) with point defects is one of the most promising candidates as a single photon emitter for high photostability, ultrahigh brightness, nonlinearity, and narrow emission line width. In applying hBN with a single point defect to those applications, three-dimensional determination of its dipole orientation is critically important. In this paper, we three-dimensionally determine the dipole orientation of single defects in hBN nanoflakes. By measuring the second-order correlation function and emission spectra, hBN nanoflakes with single defects were found from hBN nanoflakes placed on microscope coverslips. High-resolution emission intensity patterns were measured by exciting the defects in the hBNs with a focused radially polarized beam and azimuthally polarized beam. By comparing these patterns with theoretical calculations, we determined the polar angle and azimuthal angle of the dipole moment and found that they were oriented near the plane of the layers of the hBN nanoflakes on the microscope coverslip on which they were placed. This information is important to realize highly efficient quantum information devices in which the dipole orientation has to be precisely controlled.