  Quantum defects in diamonds have been studied as a promising resource for
quantum science. The subtractive fabrication process for improving photon
collection efficiency often require excessive milling time that can adversely
affect the fabrication accuracy. We designed and fabricated a Fresnel-type
solid immersion lens using the focused ion beam. For a 5.8 um-deep
Nitrogen-vacancy (NV-) center, the milling time was highly reduced (1/3
compared to a hemispherical structure), while retaining high photon collection
efficiency (> 2.24 compared to a flat surface). In numerical simulation, this
benefit of the proposed structure is expected for a wide range of milling
depths.
