Third-generation gravitational wave observatories, such as the Einstein Telescope (ET) and Cosmic Explorer, aim for sensitivity improvements of at least a factor of ten over a wide frequency range compared to the current operational detectors. To finalise the design of these third generation detectors and to further develop and qualify their subsystems, dedicated test facilities are required. The ETpathfinder prototype consists of full interferometer configurations and aims to provide a high sensitivity test facility in a similar environment as ET. The key technologies that will be implemented are lasers and optics at 1550 nm and 2090 nm, silicon test masses, cryogenic cooling techniques, and advanced quantum-noise reduction schemes. In these proceedings we will present a general status update of the ETpathfinder experiment.
collaboration et al. (2026) studied this question.