Optical quantum interferometry represents the oldest example of quantum metrology and it is at the source of quantum technologies. The original squeezed state scheme is now a significant element of the last version of gravitational wave detectors and various additional uses have been proposed. Further quantum enhanced schemes, from SU(1,1) interferometer to twin beam correlation interferometry, have also reached the stage of proof of principle experiments enlarging the field of experimental quantum interferometry and paving the way to several further applications ranging from Planck scale signals search to small effects detection. In this review paper I introduce these experimental achievements, describing their schemes, advantages, applications and possible further developments.
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