Speaker
Description
Current state-of-the-art gravitational wave observatories around the world, LIGO, Virgo, and KAGRA, have enabled the detection of $90$ gravitational waves, with an additional $200$ events in the ongoing O4 observing run [ref]. This is achieved through strain sensitivities in the order from $10^{-18} 1/\sqrt{Hz}$ to $10^{-23} 1/\sqrt{Hz}$ [ref,ref], where current noise requirements of test mass motion at 10 Hz are $10^{-19} m/\sqrt{Hz}$ [ref]. Next-generation detectors, such as the Einstein Telescope [ref,ref], are envisioned to achieve amplitude-spectral-density strain sensitivities on the order of $10^{-24} m/\sqrt{Hz}$ with a broader frequency range [ref,ref], allowing us to address a huge number of key issues related to astrophysics, fundamental physics, and cosmology [ref]. Especially in the low-frequency band, these sensitivities can only be obtained by reducing thermal noise on the mirror and its suspension [ref]. This means that cryogenic cooling is necessary for the Einstein telescope to acquire the desired sensitivities.
Leiden Institute of Physics hosts several research groups specializing in ultra-low temperature experiments, requiring ultra-low vibration levels. Ongoing experiments in our group have demonstrated $30fm/\sqrt{Hz}$ in a cryogenfree dilution refrigerator at $27 Hz$ [ref]. We aim to push this noise floor in a narrow bandwidth to $10^{-15}m/\sqrt{Hz}$ at frequencies of order $10 Hz$. Here, we show the current experimental setup of the Zeppelin experiment [ref], focusing on the vibration isolation system currently employed. We also share preliminary results, including force noise measurements and mode cooling.
Further research will focus on improving the vibration isolation system by co-developing systems designed for the Einstein telescope. The added complexity arising from extra vibrations due to the cooling system will be discussed. This will also include measurements and analysis of cryogenic acceleration sensors to characterize vibrations at millikelvin temperatures.
