Biphotons,squeezing, and new states of light in polarization quantum optics

The concept of squeezing is discussed for multimode quantum light beams with consideration of polarization using the polarization gaugeSU (2) invariance of free electromagnetic fields. We separate the polarization and biphoton degrees of freedom from other ones, and consider uncertainty relations characterizing polarization and biphoton observables. As a consequence, we obtain a new classification of polarization states of light within quantum optics. We also discuss briefly some interrelations of our analysis with experiments related to some fundamental problems of physics.