Seismic isolation systems for next-generation gravitational wave detectors

Gravitational Wave (GW) Astronomy is becoming a revolutionary method for studying the Universe and understanding its evolution, opening a new frontier in the exploration of cosmic phenomena. Third-generation ground-based gravitational wave interferometers, expected to be built around 2035, will be an order of magnitude more sensitive than the current detectors. Their low frequency sensitivity will allow the detection of binary compact coalescences up to high red-shift improving the capability to study intermediate-mass black holes and enhancing early alerts of binary neutron star coalescences. Within this scientific contest an important effort is being made to increase the detection capabilities in a frequency range down to 3 Hz and mitigating low-frequency noise. The Superattenuator is the mechanical device designed to isolate the optical components of the Advanced VIRGO (AdV) interferometer from seismic noise and local disturbances, relying on the passive and active action of the elements. In this short note, we summarize the design activity around new generation of seismic attenuation systems with the intent to improve the sensitivity in the low frequencies region. The optimization of prototypes and their passive attenuation performance is also considered in view of the Einstein Telescope with the possibility to decrease the size of the mechanical structure and minimizing the impact on the civil works for the construction of the underground laboratory.