Аннотация:Quantum measurement of a small force with an error less than the standard quantum limit using
a lossless optical interferometric sensor is discussed. The detector sensitivity has been
investigated taking into account its nonlinearity. The case when the measurement time is shorter
than the relaxation time of the optical cavity is considered. The conditions when the
equations can be linearized in principle have been determined, and the limit sensitivity of the
detector has been calculated with due account of the nonlinearity in the detection of the
quadrature component of the reflected optical wave. Two methods for reducing the negative effect
of nonlinearity have been proposed: ~a! using nonlinear detection of the output optical wave
~to measure the number of photons in the biased wave!; ~b! introducing additional nonlinearity to
mechanical components of the device. Numerical estimates are given.