Quenching the thermal noise down to the quantum limit

Thermal noise in mechanical suspension systems is presently the most severe limitation to the sensitivity of the new generation of interferometric gravitational wave detectors, like VIRGO and LIGO, in the frequency range between 5 and 500 Hz. For this reason, a few experimental groups around the world are challenging the strategic goal of quenching thermal noise effects. Here we address present strategies, present some experimental data and discuss theoretical and experimental implications of such a task by pointing out present limits and still unsolved problems.