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

TL;DR

CHRONOS is a proposed cryogenic gravitational-wave detector operating in the sub-Hz band, using innovative configurations to overcome noise challenges and enable new astrophysical and geophysical applications.

Contribution

The paper evaluates the noise budget of CHRONOS using simulations, demonstrating its potential sensitivity and feasibility for low-frequency gravitational-wave detection and earthquake early warning.

Findings

Achieves strain sensitivity of ~10^{-18} Hz^{-1/2} at 2 Hz.

Capable of detecting stochastic background of ~2×10^{-3} at 2 Hz.

Potential to provide faster earthquake warnings by detecting gravity-gradient signals.

Abstract

CHRONOS is a proposed gravitational-wave detector designed to operate in the sub-Hz frequency range (0.1 to 10 Hz), a largely unexplored band due to strong noise sources that hamper ground-based detectors. It employs cryogenic operation, a cross torsion-bar configuration, a triangular Sagnac interferometer, and a speed meter readout scheme to overcome key noise limitations, targeting a strain sensitivity of $h \sim 10^{-18} Hz^{-1/2}$ around 2 Hz and a stochastic gravitational wave background of $\Omega_{GW}$ approximately $2 \times 10^{-3}$ 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.