Ultrahigh Q pendulum suspensions for gravitational wave detectors

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Abstract
Pendulum suspensions for laser interferometer gravitational wave detectors need to have an extremely high Q factor to minimize Brownian motion noise. In this paper we analyze the limits to the Q factor of the compound pendulum. We show that the observed acoustic loss of niobium can allow pendulum Q factors of 1010 to be achieved. This should enable a 3 km terrestrial laser interferometer detector to achieve strain sensitivity of 10−22/√Hz at frequencies as low as 10 Hz. At cryogenic temperatures Q factors up to 1012 should be achievable.