Quantum limits of interferometer topologies for gravitational radiation detection

In order to expand the astrophysical reach of gravitational wave (GW) detectors, several interferometer topologies have been proposed, in the past, to evade the thermodynamic and quantum mechanical limits in future detectors. In this work, we make a systematic comparison among these topologies by considering their sensitivities and complexities. We numerically optimize their sensitivities by introducing a cost function that tries to maximize the broadband improvement over the sensitivity of current detectors. We find that frequency-dependent squeezed-light injection with a 100 m scale filter cavity yields a good broadband sensitivity, with low complexity, and good robustness against optical loss. This study gives us a guideline for the near-term experimental research programs in enhancing the performance of future GW detectors.