  KAGRA is the first large-scale gravitational-wave detector with cryogenic
test masses. Its target sensitivity is limited mostly by quantum noise in the
observation frequency band owing to the remarkable reduction of thermal noise
at cryogenic temperatures. It is thus essential to reduce quantum noise, and
KAGRA is designed to implement two quantum noise reduction techniques. KAGRA
has already started considering an upgrade plan, in which a few more new
quantum noise reduction techniques will be incorporated. In this article, we
report the currently implemented quantum noise reduction techniques for KAGRA
and those that will be implemented in the near future.
