  We experimentally demonstrate high-Q cavity formation at an arbitrary
position on a silicon photonic crystal waveguide by bringing a tapered
nanofiber into contact with the surface of the slab. An ultrahigh Q of 5.1 x
10^5 is obtained with a coupling efficiency of 39%, whose resonant wavelength
can be finely tuned by 27 pm by adjusting the contact length of the nanofiber.
We also demonstrate an extremely high coupling efficiency of 99.6% with a
loaded Q of 6.1 x 10^3. In addition, we show that we can obtain an all-pass
filter type coupled resonator system, which has the potential to be used for
slow light generation.
