Over the years gravitational waves detectors have increased their sensitivity and are now more and more limitated by the standard quantum limit. This quantum noise which is inherent to quantum mechanics and which is a direct consequence of the Heisenberg uncertainty principle cannot be suppressed. However it is possible to overcome this limit without violating the laws of physics by using a particular state of light called squeezed light. Moreover, the limiting quantum noise is different if looking at the low frequency range or high frequency range of Virgo, in the first case the limitation is due to the radiation pressure fluctuations on the 3km cavity mirrors whereas in the second case the limitating factor is shot noise. Thus, to achieve quantum noise reduction in the whole Virgo frequency range, squeezing has to be made frequency dependent in order to be able to choose between amplitude squeezing at low frequency and phase squeezing at high frequency, this is done using a filter cavity.

Exsqueez is a project in collaboration with four labs, LKB, IJCLab (ex-LAL), LAPP and IP2I (ex-LMA) which aims to demonstrate Frequency Dependent Squeezing using the already existing 50m cavity from the Calva facility and by implementing a squeezed light source under vacuum. Also, the overall configuration is kept similar to Virgo (same electronics, same vacuum compatible photodiodes, optical coatings done at LMA, same softwares).

This seminar will present squeezed light and quantum noise in gravitational wave detectors before focusing on the Exsqueez experiment which is currently installed at IJCLab and its future evolutions aiming to implement a variable finesse filter cavity to adapt the squeezed field to different Virgo interferometer configurations.