The 10 m Prototype Interferometer is a test bed to develop techniques for upgrades of the gravitational wave detector GEO 600. These include, for example, new high-power lasers, advanced seismic isolation, and the reduction of quantum noise. Furthermore, the prototype facility, with its large ultra-high vacuum system, excellent seismic isolation, well stabilized high-power laser, and fully digitally control infrastructure, allows experiments to be conducted that would not be possible otherwise. These experiments aim at obtaining a better understanding of how quantum mechanical effects can govern the macroscopic world. A 10 m Michelson interferometer is set up which is solely limited by quantum noise— photon shot noise at high frequencies and quantum back-action noise at low frequencies.

This sensitivity, until recently thought to be the ultimate limit in interferometry, is referred to as Standard Quantum Limit (SQL). However, even this remarkable sensitivity can be overcome by the application of innovative techniques such as the injection of squeezed vacuum states.

To reach the SQL, several innovative approaches and techniques must be employed: To reduce thermal noise, the optical components will be individually suspended from silica fibres as the last stage of a multiple cascaded pendulum system. These are mounted on passive isolation tables, which are interferometrically interconnected. To minimise thermal noise from the mirror coatings, we use anti-resonant Fabry-Perot cavities as compound mirrors.

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