  Point defects in crystals provide important building blocks for quantum
applications. To initialize, control, and read-out their quantum states, an
efficient optical interface for addressing defects with photons is required.
However, conventional confocal fluorescence microscopy with high refractive
index crystals has limited photon collection efficiency and spatial resolution.
Here, we demonstrate high resolution, high contrast imaging for defects qubits
using microsphere-assisted confocal microscopy. A microsphere provides an
excellent optical interface for point defects with a magnified virtual image
that improves spatial resolution up to ~${\lambda}$/5 as well as an optical
signal-to-noise ratio by four times. These features enable individual optical
addressing of single photons and single spins of spatially-unresolved defects
in conventional confocal microscopy with improved signal contrast. The combined
optical tweezers show the possibility of positioning or scanning the
microspheres for deterministic coupling and wide-field imaging of defects. The
approach does not require any complicated fabrication and additional optical
system but uses simple micro-optics off-the-shelf. From these distinctive
advantages of the microspheres, our approach can provide an efficient way for
imaging and addressing closely-spaced defects with higher resolution and
sensitivity.
