  We report on high efficency coupling of individual air-suspended carbon
nanotubes to silicon photonic crystal nanobeam cavities. Photoluminescence
images of dielectric- and air-mode cavities reflect their distinctly different
mode profiles and show that fields in the air are important for coupling. We
find that the air-mode cavities couple more efficiently, and estimated
spontaneous emission coupling factors reach a value as high as 0.85. Our
results demonstrate advantages of ultralow mode-volumes in air-mode cavities
for coupling to low-dimensional nanoscale emitters.
