Experimental equipment - Evaluation

A confocal laser scanning microscope (CFM) is used to observe the formed color center. In our research, we operate multiple self-made CFM devices and use them to measure color centers.

CFM observation using a 532nm laser is possible. A schematic diagram of the microscopy system is shown. A 532nm green laser is used to excite the color centers. After shaping the beam into TEM₀₀ using a single mode (SM) fiber, the laser is irradiated onto the diamond through a high N.A. objective lens. The laser spot diameter is focused so small that it approaches the diffraction limit. Fluorescence from the color center passes through a confocal optical system with a pinhole placed between a pair of convex lenses, passes through a filter that excludes excitation light, and then enters a single photon detector (Si avalanche photodiode). By scanning the objective lens with a piezo stage that has a positional accuracy of about 1 nm, a CFM image like the one shown in the figure can be obtained. The reason why a half mirror is placed just in front of the single photon detector is to prove that the color center is single by measuring the intensity correlation between the two single photon detectors. As shown in the figure, it is possible to prove that the color center is single from the results of second-order correlation function measurements (anti-bunching measurements) using a Hanbury Brown-Twiss interferometer.

Fig. (a) Schematic diagram of the CFM (b,c) Pictures of the CFM

Fig. CFM images

Fig. Anti-bunching effect from a single color center

The figure shows Rabi oscillation of a single electron spin in the NV center. This NV center is an NV center created by ion implantation method. By optimizing the ion implantation and heat treatment conditions, we have the longest spin coherence time of any NV center created by ion implantation.

Fig. Rabi oscilation of an electron spin of the single NV center