Enhancing the Fluorescence Brightness of Single SiC Spin Color Center

Enhancing the Fluorescence Brightness of Single SiC Spin Color Center

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The solid-state spin color center is an important system for quantum information processing, and its fluorescence brightness is an important parameter towards practical quantum applications. Coupling with solid-state micro/nanostructures to achieve fluorescence enhancement of spin centers is a commonly used method. Various solutions, including processing solid infiltrating lenses, nanorods, bull eye rings, photonic crystal microcavities, and fiber optic cavities have proposed and implemented. However, there are still many challenging issues to be addressed in this direction, such as the susceptibility of color center spin properties to complex micro/nano fabrication processes, and the difficulty in aligning color centers with micro/nano structures.

1. Enhancing Fluorescence of SiC Spin Centers by Plasmons

Researchers use plasmons to enhance the fluorescence of spin centers in silicon carbide. The research group prepared SiC thin films with a thickness of about 10um through processes such as chemical mechanical polishing, and used ion implantation technology to prepare near surface (about 15 nm) double vacancy color centers in the films. Subsequently, the thin film was flipped over and pasted onto a silicon wafer coated with coplanar gold waveguides using van der Waals forces. This allowed the distance between the near surface color center and the gold waveguide to fall within the range of surface plasmons, thereby enhancing color center fluorescence.

In previous work, the research group first discovered that a single double vacancy PL6 color center in silicon carbide has luminescence brightness and spin readout contrast comparable to diamond NV color centers at room temperature [Natl. Sci. Rev. 9, nwab122 (2022)]. In this work, an objective with a numerical aperture of 0.85 was used, and the enhancement effect of surface plasmons was utilized to achieve a 7-fold enhancement of the brightness of a single PL6 color center; Further using an oil mirror with a numerical aperture of 1.3, the color center fluorescence can exceed 1 million counts per second. The research team also used reactive ion etching technology to regulate the thickness of the film, accurately controlling the distance between the near surface color center and the coplanar waveguide, and studying the optimal range of action. In addition to generating surface plasmons, coplanar gold waveguides can also be used for efficient microwave radiation, greatly improving spin manipulation efficiency. Compared to traditional microwave radiation methods, coplanar waveguides increase the Rabi frequency of a single PL6 color center by 14 times at the same microwave power. The experimental setup and results are shown in Fig. 1.

Fig. 1 Experimental setup and result diagram of Enhancing the Fluorescence Brightness of Single SiC Spin Color Center

Fig. 1 Experimental setup and result diagram. (a) Schematic diagram of a device based on surface plasmon enhancement; (b) Comparison of confocal fluorescence scans with and without enhanced (left) regions of plasmon resonance; (c) Comparison of saturated fluorescence counts between a single PL6 color center enhanced by plasmons and an unenhanced single PL6 color center in the bulk material; d) Comparison of Rabi oscillation frequencies measured using gold waveguides and copper wires at different microwave powers.

2. Research on Fluorescence Enhancement Mechanism of Single SiC Spin Color Center

The research group also conducted in-depth research on the fluorescence enhancement mechanism. By using a three-level model to fit the autocorrelation function and measuring the lifetime of non resonant excited fluorescence, the research group not only verified that surface plasmons enhance fluorescence brightness by increasing the radiation transition rate of the color center energy level, but also found that the quenching effect of surface plasmons leads to a decrease in the fluorescence brightness of the color center as the operating distance gradually decreases.

This work achieves, for the first time, plasmon enhancement of near surface spin color center fluorescence in SiC thin films. The preparation of coplanar gold waveguides is simple, without the need for complex enhancement structures and alignment processes, and this method is also suitable for fluorescence enhancement of other spin centers in silicon carbide. This technology will strongly promote the application of SiC materials in the quantum field.


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