I present how to obtain and characterize quantum states of light potentially useful for quantum communication protocols. The control of the frequency correlations,\ud
and the bandwidth, of single and paired photons is an essential ingredient in specific quantum applications, from quantum imaging to quantum clock synchronization.\ud
I show both theoretical and experimental spectral correlations of pairs of photons generated in non-collinear spontaneous parametric down conversion (SPDC). In the second part of the work, a scheme for quantum key distribution using the two-way LM05 protocol [PRL 94, 140501 (2005)] and its implementation is presented too. A preliminary transmission test is discussed together with\ud
an experimental study for the security of the generated key in presence of noise in the channels. The noise is modulated as to simulate the effect of an eavesdropper.\u
