  Broadband multimode squeezers constitute a powerful quantum resource with
promising potential for different applications in quantum information
technologies such as information coding in quantum communication networks or
quantum simulations in higher dimensional systems. However, the
characterization of a large array of squeezers that coexist in a single spatial
mode is challenging. In this paper we address this problem and propose a
straightforward method to determine the number of squeezers and their
respective squeezing strengths by using broadband multimode correlation
function measurements. These measurements employ the large detection windows of
state of the art avalanche photodiodes to simultaneously probe the full Hilbert
space of the generated state, which enables us to benchmark the squeezed
states. Moreover, due to the structure of correlation functions, our
measurements are not affected by losses. This is a significant advantage, since
detectors with low efficiencies are sufficient. Our approach is less costly
than full state tomography methods relying on multimode homodyne detection
which build on much more demanding measurement and analysis tools and appear to
be impractical for large Hilbert spaces.
