  The intracavity topologies of laser gravitational-wave detectors are the
promising way to obtain sensitivity of these devices significantly better than
the Standard Quantum Limit (SQL). The most challenging element of the
intracavity topologies is the \emph{local meter} which has to monitor position
of a small ($1\div10$ gram) local mirror and which precision defines the
sensitivity of the detector.
  To overcome the SQL, the quantum variational measurement can be used in the
local meter. In this method a frequency-dependent correlation between the meter
back-action noise and measurement noise is introduced, which allows to
eliminate the back-action noise component from the meter output signal. This
correlation is created by means of an additional filter cavity.
  In this article the sensitivity limitations of this scheme imposed by the
optical losses both in the local meter itself and in the filter cavity are
estimated. It is shown that the main sensitivity limitation stems from the
filter cavity losses. In order to overcome it, it is necessary to increase the
filter cavity length. In a preliminary prototype experiment about 10 meter long
filter cavity can be used to obtain sensitivity approximately $2\div3$ times
better than the SQL. For future QND gravitational-wave detectors with
sensitivity about ten times better than the SQL, the filter cavity length
should be within kilometer range.

General Relativity and Quantum Cosmology