Noise budget of Cryogenic sub-Hz cROss torsion-bar detector with quantum NOn-demolition Speed meter (CHRONOS)

Abstract

CHRONOS is a proposed gravitational-wave detector designed to operate in the sub-Hz frequency (0.1–10 Hz) band, a largely unexplored range due to strong noise sources that hamper ground-based detectors. It employs cryogenic operation, cross torsion-bar configuration, triangular Sagnac interferometer, and speed meter readout scheme to overcome key noise limitations, targeting a strain sensitivity of h ∼ 10⁻¹⁸ Hz^−1/2 around 2 Hz and a stochastic gravitational wave background of Ω_GW ~ 2 × 10⁻³ at 2 Hz. Using analytical and interferometric simulations with FINESSE3, we evaluate the noise budget of CHRONOS and characterize the relative contributions of quantum, thermal, and environmental noise sources. Our results demonstrate that CHRONOS achieves competitive sensitivity at low frequencies. The feasibility of using CHRONOS in an earthquake early-warning system by detecting prompt gravity-gradient signals is also investigated, and is predicted to be faster by approximately 2.92 to 6.90 seconds within 40 km. These findings highlight the scientific potential of CHRONOS, bridging gravitational-wave astronomy and geophysical monitoring, and motivating further development of low-frequency detector technologies.