  Nonclassical states of light are an important resource in today's quantum
communication and metrology protocols. Quantum up-conversion of nonclassical
states is a promising approach to overcome frequency differences between
disparate subsystems within a quantum information network. Here, we present the
generation of heralded narrowband single photons at 1550 nm via cavity enhanced
spontaneous parametric downconversion (SPDC) and their subsequent up-conversion
to 532 nm. Quantum non-Gaussianity (QNG), which is an important feature for
applications in quantum information science, was experimentally certified for
the first time in frequency up-converted states.
