Fast imaging of multimode transverse-spectral correlations for twin photons

Hyperentangled photonic states - exhibiting nonclassical correlations in several degrees of freedom - offer improved performance of quantum optical communication and computation schemes. Experimentally, a hyperentanglement of transverse-wavevector and spectral modes can be obtained in a straightforward way with multimode parametric single-photon sources. Nevertheless, experimental characterization of such states remains challenging. Not only single-photon detection with high spatial resolution - a single-photon camera - is required, but also a suitable mode-converter to observe the spectral/temporal degree of freedom. We experimentally demonstrate a measurement of a full 4-dimensional transverse-wavevector-spectral correlations between pairs of photons produced in the non-collinear spontaneous parametric downconversion (SPDC). Utilization of a custom ultra-fast single-photon camera provides high resolution and a short measurement time.