Polarization Dynamics of Solid-State Quantum Emitters

Abstract

Quantum emitters in solid-state crystals have recently attracted a great deal of attention due to their simple applicability in optical quantum technologies. The polarization of single photons generated by quantum emitters is one of the key parameters that plays a crucial role in various applications, such as quantum computation, which uses the indistinguishability of photons. However, the degree of single-photon polarization is typically quantified using the time-averaged photoluminescence intensity of single emitters, which provides limited information about the dipole properties in solids. In this work, we use single defects in hexagonal boron nitride and nanodiamond as efficient room-temperature single-photon sources to reveal the origin and temporal evolution of the dipole orientation in solid-state quantum emitters. The angles of the excitation and emission dipoles relative to the crystal axes were determined experimentally and then calculated using density functional theory, which resulted in characteristic angles for every specific defect that can be used as an efficient tool for defect identification and understanding their atomic structure. Moreover, the temporal polarization dynamics revealed a strongly modified linear polarization visibility that depends on the excited-state decay time of the individual excitation. This effect can potentially be traced back to the excitation of excess charges in the local crystal environment. Understanding such hidden time-dependent mechanisms can further improve the performance of polarization-sensitive experiments, particularly that for quantum communication with single-photon emitters.

Quantitative Investigation of Quantum Emitter Yield in Drop-Casted Hexagonal Boron Nitride Nanoflakes

“…Although spectral diffusion data have not been investigated here for all experimental conditions, prior systematic studies utilizing a broad range of solvents show no significant alterations to their spectra, , which is in line with our observations at these time scales . Emission at this wavelength suggests a defect source due to carbon atoms according to the literature. , However, slight peak position variations between measured nanoflakes (Figure c) indicate the potential occurrence of multiple defect types. To verify the nanoflakes as SPEs, we have performed second-order correlation measurements g (2) (τ), revealing low correlations of g (2) (τ = 0) = 0.11 ± 0.015, indicative of single-photon sources (Figure e).…”

Narrowband Quantum Light Emission from Oxygen-Related Color Centers in Hexagonal Boron Nitride

“…These results are in qualitative agreement with a comprehensive recent DFT study of 126 native carbon- and oxygen-based color centers residing in hBN in their various charge configurations . The work predicts a largely absent emission/absorption dipole misalignment for many carbon-related defects such as C B V N , C N V N , or C B C N C B C N , while several oxygen-related defects typically show values between 0 and 40° depending on the microscopic structure and charge state.…”

“…The emitted light is further characterized by pronounced single photon antibunching and a high linear DOP of 79%, with a misalignment between emission and absorption dipole of about 20°. The latter is also in qualitative agreement with DFT calculations that show little to no dipole orientation for carbon-based emitters while, for example, oxygen replacing boron (O B ) defects in the negative charge state emit at 736 nm with 32° dipole misalignment; however, an exact microscopic origin of the color center cannot be assigned. The temporal dynamics recorded on a 1 s time scale reveals spectral diffusion-free and blinking-free emission at a ZPL of 753 nm, even when residing directly on SiO 2 , implying an excellent RT photostability without utilizing additional passivation techniques.…”

“…A negatively charged V B O N – center is another possible candidate with a predicted ZPL energy around 1.97 (630 nm), i.e., in the same spectral range, that was also shown to display a strong spin response in electron paramagnetic resonance (EPR) experiments . DFT calculations for oxygen-related color centers in hBN further proposed that the emission carries a polarization and the excitation and emission dipoles are misaligned based on the exact charge distribution of the color centers, e.g., oxygen-related versus carbon-related. , Therefore, we studied the polarization behavior of hBN QE to compare with the theoretical results to shed additional light on the microscopic origin of the emission in our samples. The polar plot in Figure a,b indicates a linear polarization state for both oxygen-related and carbon-related emissions.…”

“…Combining the predicted ZPL wavelength and the emission dipole angle one can narrow down the selection to some extent. For example, oxygen replacing boron (O B ) defects in the negative charge state emit at 736 nm with 32° dipole misalignment seem plausible, while O N with infrared emission at 4795 nm and 11.8° rotation can be ruled out.…”