Quantum Characterization of Single Photon Detectors

The research activities described in this thesis have basically an experimental profile, and were realized in the Quantum Optics Laboratories of the Optic Division in the Istituto Nazionale di Ricerca Metrologica (I.N.Ri.M.). The experiments presented here are oriented to the characterization of single- and few-photon detectors calibration, exploiting quantum properties. The first chapter has an introductory character, oriented to the study of nonlinear optics phenomena and focused in the spontaneous parametric down conversion (PDC) process. After the quantization of the free electromagnetic field, we recall the quantum theory of PDC. In the second chapter the Klyshko's two-photon calibration technique is presented and applied to an Avalanche Photo Diode (APD) based single photon counting module. Chapter three is an introduction to quantum measurements and quantum operation theories where the concept of positive-operator valued measurement (POVM) is presented. In chapter four, the quantum characterization of a true photon-number resolving detector (PNRD) based on a transition edge sensor (TES) is presented. In this experiment, the POVM of the TES is reconstructed by realizing a tomography of the detection process's quantum operation, using as a probe a set of known coherent states. In the fifth and last chapter, the POVM of a tree type PNRD is reconstructed exploiting strong quantum correlations of PDC twin beams