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Description
The Torsion-Bar Antenna (TOBA) is a ground-based gravitational wave detector sensitive to the low-frequency band of 0.1 Hz - 10 Hz. TOBA consists of two horizontally suspended bar-shaped test masses (torsion pendulums) and a laser interferometer. Gravitational waves can be observed by detecting the rotation of the torsion pendulums induced by the waves using the laser interferometer. Currently, a prototype detector, Phase-III TOBA, is under development. The design sensitivity of Phase-III TOBA is at 0.1 Hz. To improve the sensitivity, it is essential to reduce noises such as the quantum noise of the laser, seismic noise, and the thermal noise of the suspension wires. In TOBA, we aim to reduce the thermal noise of the suspension wires by combining a cryogenic environment with crystalline fibers, and we are developing a suspension system that exhibits a high Q-factor at low temperatures. Sapphire fibers are planned to be used as the suspension wires. This poster presents the current status of the Q-factor measurement of a sapphire fiber under cryogenic conditions.