Figure 5.

Optical Q-factors measured for different optical resonators and expected maximum enhancement based on the mode volume design F_{p, max} he cavity coupled with color centres are indicated with star. Data from Refs. 1,10,50,51,54,55,57–68. We observe that the experimental Q-factors generated when the same cavity is coupled to a color center tend to be much smaller compared to an unloaded cavity and the F_SE tends to be much smaller compared to the expected F_{p, max}. By way of an example in Ref. 50 a measured loaded Q-factor of 3000 (theoretical Q=6000) is achieved with a record F_SE=70, while the expected F_{p, max}~260 based on the cavity mode volume. In Ref. 51 F_SE=63 while the expected F_{p, max}~194.