Deterministic generation of single B centers in hBN by one-to-one conversion from UV centers

TL;DR

The study addresses deterministic creation of single B centers in hBN by in-situ monitoring of UV-to-blue center interconversion under electron irradiation. Using an avalanche photodiode–assisted CL setup, the authors observe anticorrelated activation of B centers with UV centers, enabling one-to-one UV-to-B transformations and real-time heralding of single-emitter creation. They demonstrate an array of single emitters with heralded activation and further refine emitter control via selective photobleaching, achieving near-ideal single-emitter distributions. These results support a vertical carbon-dimer microscopic model for B centers and pave the way for deterministic, top-down integration of single-photon emitters into photonic devices.

Abstract

Among the variety of quantum emitters in hexagonal boron nitride (hBN), blue-emitting color centers, or B centers, have gathered a particular interest owing to their excellent quantum optical properties. Moreover, the fact that they can be locally activated by an electron beam makes them suitable for top-down integration in photonic devices. However, in the absence of a real-time monitoring technique sensitive to individual emitters, the activation process is stochastic in the number of emitters, and its mechanism is under debate. Here, we implement an in-situ cathodoluminescence monitoring setup capable of detecting individual quantum emitters in the blue and ultraviolet (UV) range. We demonstrate that the activation of individual B centers is spatially and temporally correlated with the deactivation of individual UV centers emitting at 4.1 eV, which are ubiquitous in hBN. We then make use of the ability to detect individual B center activation events to demonstrate the controlled creation of an array with only one emitter per irradiation site. Additionally, we demonstrate a symmetric technique for heralded selective deactivation of individual emitters. Our results provide insights into the microscopic structure and activation mechanism of B centers, as well as versatile techniques for their deterministic integration.

Figures (6)

• Figure 1: (a) Scheme of the experimental setup. AWG: arbitrary waveform generator. (b) Black line: CL spectrum of a hBN sample containing UV and blue emitters. Violet shading: UV filter passband. Blue shading: Blue filter passband. The visible-range part of the spectrum was taken with a UV filter to suppress second-order refraction of the exciton emission.
• Figure 2: (a) Series of CL bandpass images of color centers in a hBN flake of thickness 145 nm with a current intensity of $I = 0.024$ nA. The top row shows the signal measured in the UV detection channel and the bottom row displays the signal measured in the blue detection channel. The scale bar indicates 500 nm. The circles labeled A to E indicate the state of five emitters: a red circle indicates the color center is off, a green circle indicates the emitter is on, and a two-colored circle indicates that an activation or deactivation is taking place. The states of the blue and UV emitters occupying these five positions are anticorrelated. (b) and (c) Consecutive CL scans of two fixed emitters in the UV (top) and blue (bottom) spectral range, showing switching between the two states.
• Figure 3: Representative CL timetrace measured by the blue detection channel during a continuous irradiation of a fixed location on a 130 nm flake with $I = 0.021$ nA.
• Figure 4: (a) CL intensity trace of the blue detection channel: at $t_{1}$ the $e^{-}$ beam is turned on, at $t_{2}$ a single B center is generated and at $t_{3}$ the $e^{-}$ beam is turned off. (b) PL map of a $4 \times 2$ array of B centers activated in a 50 nm thick flake, with a distance of 1 $\mu$m between irradiation sites. The scale bar indicates 500 nm. The orange circle indicates the individual B center characterized in Fig. \ref{['Array']}c and the dotted orange circle denotes the irradiation site characterized in Fig. \ref{['Bleaching']}. (c) $g^{(2)}(\tau)$ measured for the B center circled in orange in the PL map, with $g^{(2)}(0) = 0.09 \pm 0.03$. Orange dashed line: Classical limit.
• Figure 5: (a) Blue line: $g^{(2)}(\tau)$ measured from the brightest B-center in the PL map (dashed orange circle in Figure \ref{['Array']}b). Black line: Fit to the data, where $g^{(2)}(0) = 0.67 \pm 0.05$ (b) PL timetrace measured during the selective photobleaching procress; $t_{1}$: the laser is turned on with a neutral density filter, yielding a 750 $\mu$W power; $t_{2}$: the absorption filter is removed, so that the excitation power increases to 7.5 mW; $t_{3}$: a B-center has been deactivated; $t_{4}$: the absorption filter is inserted back. (c) Blue line: $g^{(2)}(\tau)$ measured at the same position after the photobleaching process. Black line: fit to the data, providing $g^{(2)}(0) = 0.29 \pm 0.11$.