  Gravitational wave observation has the potential of probing ultralight
bosonic fields such as axion. Axion forms a cloud around a rotating black hole
(BH) by superradiant instability and should affect the gravitational waveform
from binary BHs. On the other hand, considering the cloud associated with a BH
in a binary system, tidal interaction depletes the cloud in some cases during
the inspiral phase. We made the exhaustive study of cloud depletion numerically
in a wide parameter range for equal mass binaries, assuming only the
quadrupolar tidal perturbation is at work. We found that clouds can avoid
disappearing due to the tidal effect only when $l=1$ mode is the fastest
growing mode and when the binary orbit is counter-rotating in the
non-relativistic parameter region.
