High-Q/V air-mode photonic crystal cavities at microwave frequencies
  We present results for a photonic microwave resonator designed and fabricated at 17.4GHz with a record high Quality factor (Q = 26,400) at room temperature over a mode volume smaller than one cubic wavelength. The cavity is uniquely designed to have its electric field concentrated in air, which allows for efficient coupling to free space and facilitates interactions with gaseous atomic systems and fluids. 
Yinan Zhang, Irfan Bulu, Wai-Ming Tam, Ben Levitt, Jagdish Shah,   Tancredi Botto, Marko Loncar
physics.optics