Аннотация:We investigate both theoretically and experimentally strong correlations in macroscopic (bright) quantum
states of light generated via unseeded parametric down-conversion and four-wave mixing. The states generated
this way contain only quantum noise, without a classical component, and are referred to as bright squeezed
vacuum (BSV). Their important advantage is the multimode structure, which offers a larger capacity for the
encoding of quantum information. For the theoretical description of these states and their correlation features
we introduce a generalized fully analytical approach, based on the concept of independent collective (Schmidt)
modes and valid for the cases of both weak and strong nonlinear interaction. In experiment, we generate states of
macroscopic BSV with up to 1010 photons per mode and examine large photon-number spatial correlations that
are found to be very well described by our theoretical approach.