  Achieving the quantum noise targets of third-generation detectors will
require 10 dB of squeezed-light enhancement as well as megawatt laser power in
the interferometer arms - both of which require unprecedented control of the
internal optical losses. In this work, we present a novel optimization approach
to gravitational-wave detector design aimed at maximizing the robustness to
common, yet unavoidable, optical fabrication and installation errors, which
have caused significant loss in Advanced LIGO. As a proof of concept, we employ
these techniques to perform a two-part optimization of the LIGO A+ design.
First, we optimize the arm cavities for reduced scattering loss in the presence
of point absorbers, as currently limit the operating power of Advanced LIGO.
Then, we optimize the signal recycling cavity for maximum squeezing
performance, accounting for realistic errors in the positions and radii of
curvature of the optics. Our findings suggest that these techniques can be
leveraged to achieve substantially greater quantum noise performance in current
and future gravitational-wave detectors.
