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

Abstract

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. Highresolution 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.

Review on coherent quantum emitters in hexagonal boron nitride

“…Defect centers in h-BN are among the brightest single photon sources [60,61] with large Debye-Waller factor > 80 % [62], high polarization contrast [63] and high robustness [24]. The three-dimensional dipole orientation of individual defect centers has been analyzed [64,65]. High-purity single photon emission was demonstrated with spectral tunability over 6 meV by strain control [61] as well as by applied electric fields [66,67].…”

“…However, the intuitive picture of an out-of-plane distortion is supported by looking at the dipole emission directionality. For single defects in h-BN nanoflakes, which are not mechanically isolated, three-dimensional determination of the dipole orientation yielded, that the dipoles are oriented near the plane of the h-BN layers [65]. Indeed, non-isolated emitters should have dipoles located in-plane with the h-BN layers and, consequently, predominantly emit photons perpendicular to the h-BN layers.…”

Nanoscale Positioning Approaches for Integrating Single Solid‐State Quantum Emitters with Photonic Nanostructures

“…[ 42,43 ] In addition, the ability to access the far‐field images of single QDs provides the possibility of determination of the emitter's dipole orientation, which can be used to align the orientations between the dipole and the local electric field for achieving the maximal light–matter interaction. [ 44,45 ] The determination of the dipole orientation is particularly important for certain applications. One such application is the coupling of one of the split neutral exciton states to the polarized cavity mode of an asymmetric microresonator, to break the limit of 50% brightness in resonance fluorescence under the cross‐polarization configuration.…”

Hybrid device of hexagonal boron nitride nanoflakes with defect centres and a nano-fibre Bragg cavity

“…In addition to basic optical characteristics investigations, two-photon absorption using near-infrared lasers 25 and anti-Stokes excitation 26 has been realized. Also, a three-dimensional analysis of the dipole orientation of a single defect centre in hBN has been experimentally performed 15 , 27 . Moreover, the defect centres in hBN have been coupled to nanophotonic devices, such as optical nanofibres, waveguides, metamaterials, and photonic crystals 28 – 32 .…”