Beyond the standard quantum limit

A fundamental peculiarity of gravitational waves is the fact that they couple very weakly to the matter. For this reason the response of a detector can be so small to be comparable with quantum undeterminations. An important limitation for the sensitivity of future generation interferometric detectors of gravitational waves is the so-called standard quantum limit, which makes impossible to do repeated, arbitrary precision measurements of the relevant observables. It can be explained as the consequence of the measurement process' back action on the detector's dynamics. A relevant theoretical and experimental effort has been done in these years in order to study the possibility of avoiding this limitation, which is no more considered a fundamental one. In this talk after a short introduction to the SQL problem from a general point of view I discuss some proposals for detection strategies designed to evade it.