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

Abstract

The frequency band between 0.1 and 10 Hz  remains largely unexplored in gravitational-wave astronomy due to strong seismic, Newtonian, and suspension thermal noise that limit ground-based detectors. The Cryogenic sub-Hz cROss torsion-bar detector with quantum NOn-demolition Speed meter (CHRONOS) is a novel detector concept designed to access this frequency range from the ground. CHRONOS combines cryogenic torsion-bar test masses with a triangular Sagnac interferometer implementing a speed-meter readout, which suppresses quantum radiation-pressure noise and enables quantum non-demolition measurements in the sub-Hz regime. The detector targets a strain sensitivity of h ∼ 10⁻¹⁸ Hz^−1/2 around 2 Hz  and stochastic gravitational wave background of  Ω_GW ∼ 2 × 10⁻³ at 2 Hz. This sensitivity opens a new observational window between space-based detectors such as LISA and ground-based interferometers, enabling observations of intermediate-mass black hole binaries, searches for stochastic gravitational-wave backgrounds, and tests of macroscopic quantum measurements.