Squeezing and the quantization of gravitational waves

The question whether gravitational waves are quantised or not can in princi ple be answered by the help of correlation measurements. If the gravitation al waves are quantised, then there exist two possibilities: they are either completely coherent, then the value of the correlation function is a const ant, or they are only partially coherent, then the correlation function is expected to have a maximum. However, the detectors of the gravitational wav es are sensitive only to coherent waves, therefore the analogue of the Hanb ury Brown and Twiss effect cannot be exploited for the proof of the quantis ed character of the gravitational waves. If the gravitational waves are qua ntised and they are generated by the change of the background metrics then they can be in a squeezed state. It has to be noted that the squeezed state is completely coherent. In a squeezed state there is a correlation between the phase of the wave and the quantum fluctuations. It is recommended to a nalyse the data to be obtained by the gravitational detectors from the poin t of view of such correlations. An explicit formula is derived for the sque ezing parameter of the quantised gravitational waves. The head-on collision of two identical black holes is analysed.