Speaker
Description
Current state-of-the-art gravitational wave observatories around the world, LIGO, Virgo, and KAGRA, have enabled the detection of more than 90 gravitational waves, with an additional 300 candidates from observing run O4 [1]. This is achieved through strain sensitivities in the order from $10^{-23}$ $1/\sqrt{\text{Hz}}$ to $10^{-24}$ $1/\sqrt{\text{Hz}}$ [2,3], in the range of $100$ to $300$ Hz. Next-generation detectors, such as the Einstein Telescope[4,5], are envisioned to achieve amplitude-spectral-density strain sensitivities on the order of 1$0^{-25}$ $m/\sqrt{\text{Hz}}$ with a broader frequency range [6,7], allowing us to address a huge number of key issues related to astrophysics, fundamental physics, and cosmology [8]. Especially in the low-frequency band, these sensitivities can only be obtained by reducing thermal noise on the mirror and improving its suspension [9]. This means that for the Einstein telescope, cryogenic cooling is necessary, where key challenges arise creating the heatlink vibration isolation system to deliver low-vibration cooling.
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 measured $30$ $\text{fm}/\sqrt{\text{Hz}}$ displacement of an suspended mass, $O(1 \text{kg})$, in a cryogen-free dilution refrigerator at $27$ $\text{Hz}$ [10]. We aim to push this noise floor to $10^{-15}$ $\text{m}/\sqrt{\text{Hz}}$ at frequencies of order 10 Hz. Here, we show the current experimental setup and progress on superconducting magnetically levitating force sensors, focusing on the vibration isolation system currently employed. We also share results, including force noise measurements and mode damping. This will also include measurements and analysis of cryogenic acceleration sensors to characterize vibrations at millikelvin temperatures.
Furthermore, we like to share our progress on the vibration isolation system built in co-development with the systems designed for the ETpathfinder. The added complexity arising from extra vibrations due to the cooling system will be discussed.