Optical correlations, both quantum and classical, represent a fundamental resource for developing technologies, which opens unprecedented opportunities in the fields of metrology, positioning, imaging and sensing. Furthermore, the correlations existing between two or more light beams have also a theoretical interest, being of key relevance in quantum optics and quantum electrodynamics and are at the basis of the quantum information processing.
The present Research Project involves three Research Units: one theoretical, the Milano Unit (at the Physics Department of the Università degli Studi di Milano) and two experimental, the Como Unit (at the Physics and Mathematics Department of the Università degli Studi dell'Insubria) and the Torino Unit (at I.N.Ri.M.). The collaboration among the three Units is well-established and long-standing, as testified by several publications.
Within the Project, the Units will design and develop innovative, high precision measurement schemes based on the correlations existing between two or more beams of light. States of the optical field endowed with either classical or quantum correlations will be addressed and their dynamics will be investigated in realistic conditions, taking into account the losses during the propagation of the signals and the imperfections at the detection stage, that unavoidably affect the precision. In particular the Units will analyze the applications of light correlations to the imaging of photosensitive samples (sub-shot noise imaging and ghost-imaging protocols) and to the detection of faint objects in highly noisy environments (quantum illumination protocol).
The key ingredient of all the addressed protocols will be a two-mode Gaussian state of the optical radiation endowed with either classical or nonclassical correlations. Among the Gaussian states, the thermal states and the multi-mode twin-beam states will play a leading role in our proposal, being the main source of classical and quantum correlations, respectively. The source of classical correlations, that can be seen as the natural classical counterpart of the twin-beam state, will be a two-mode state produced by splitting a thermal field at a balanced beam splitter: the two beams emerging from the beam splitter exhibit purely classical correlations. On the other hand, the multi-mode twin beam will be produced by a parametric down-conversion process in nonlinear crystals. The Units will implement protocols in which one of the two beams will be addressed to a target (a beam splitter or a faint object) and the other will be used as an ancilla, whose actual use will depend on the particular protocol under consideration. Furthermore, the research will be extended to the use of a multi-mode tripartite Gaussian state as a source of conditional two-mode states, which may also exhibit a non-Gaussian character: this will offer the possibility to explore a realm completely unexploited for high precision sensing techniques.
As a matter of fact, one of the most important requirements to pursue one of the main goals of the Project, that is the realization of high precision measurement schemes, is the reliability of the detectors we will use to measure the output signals. To this aim, we will consider two possible kinds of detectors, cameras (CCD and EMCCD) and hybrid photodetectos (HPD), which have been thoroughly tested and characterized by the experimental Units involved in the Project.