The Quantum Optics Group of INRIM performs research both experimental and theoretical, devoted to the investigation of entanglement in quantum mechanics and its application to quantum technologies, such as quantum information processing and quantum metrology. More in detail, many experiments, based on the use of entangled pairs of photons, are being performed, using the "Carlo Novero " eight laboratories (devoted to the memory of Carlo Novero, who began this activity). Among them:
1. We have carried out some experiments concerning Foundations of Quantum Mechanics. In particular, we tested specific local realistic models with Bell inequalities-like experiments. We also performed research aimed at the study of the bounds of quantum correlations. An experiment on wave-particle duality was realized with various optical states as well. This activity was done in part in collaboration with Turin University. Experiments on single-photon quantumness has been carried on in collaboration with NIST and University of Geneva. Finally, an experiment aimed at visualizing Page-Wootters emergence of time phenomenon has been realized in collaboration with Pavia and Pisa Universities.
2. We partecipated to the realization of the first Italian prototype of an entanglement based quantum cryptography link in the framework of a national research program leaded by Elsag Datamat. In this context we investigated quantum key distribution and quantum secure direct communication protocols both theoretically and experimentally based on entangled photon pairs. Furthermore, we realised QKD protocols based on orthogonal states (Goldberg-Vaidman's and controfactual ones). At the moment, we are studying both quantum communication channel (fibre/open air) effects and the realisation of innovative protocols. We participate in the ETSI work group on QKD standardization.
3. Our group also investigates absolute photodector calibration using correlated photons. Beyond studies on the traditional PDC scheme, alternative methods have been developed in collaboration with Moscow University. More recently researches dealt with the calibration of analog detectors.
4. In collaboration with Turin University and INFN we are investigating the properties of colour centres in diamond as deterministic single-photon sources. This activity is developed in four dedicated laboratories and spans from the characterization of novel sources based on several types of impurities (He, Sn, Pb, etc… ) with distinctive photo-emission features, to the exploitation of those sources for the implementation of fundamental research (quantification of non-classicality, super-resolved microscopy, reconstruction of optical modes). Moreover, in recent years we started to exploit the Nitrogen Vacancy centers in diamond as high-sensitivity, nanoscale magnetic (or thermometric) sensors by exploiting techniques of Optically Detected Magnetic Resonance (ODMR), with the outlook of applying those advanced techniques in biological sensing.
5. We carried out the study of quantum states engineering, such as the realisation and characterisation of PDC sources with specific properties (also realised in microstructured materials, such as PPLN crystals and waveguides), and the study of entanglement coupling and propagation in fiber. We are also studying entanglement measures and other quantumness quantifiers of quantum optical states. Also specific investigations on peculiar properties of Gaussian states have been carried on. These activities were partially realized in collaboration with Max Planck Institute for the Science of Light and with Milan University.
6. We studied and realised single photon detection systems prototypes with reduced deadtime, exploiting multiplexing based on active optical switch (in collaboration with NIST). We worked on the characterisation of TES detectors (in collaboration with Milan University). Ancilla assisted calibration of photon-number-resolving detector characterisation has been performed in collaboration with NIST.
7. We addressed the reconstruction of photon statistic and, more recently, of the full density matrix by using on/off detectors (in collaboration with Milan and Insubria Universities). Studies on the optimality of tomographic protocols and on the tomography of POVM were realized in collaboration with Moscow and Milan Universities. A novel method for optical field modes reconstruction was developed in collaboration with NIST.
8. We realized an extremely low-noise heralded-single-photon-source (based on PPLN crystal) that does not need temporal post-selection for the emitted single-photon in collaboration with NIST and Polytechnic of Milano. Coupling enhancement of single photon sources based on impurities in diamonds by micro- and nano-structures is an on-going activity carried on in collaboration with Turin University.
9. We performed studies on the connection between Quantum Imaging and entanglement. After having realized the first Sub-Shot-Noise Quantum Imaging experiment, we also built the first setup in which Quantum Illumination was achieved. Also activities on ghost imaging have been carried out.
10. We are considering the advantages of these techniques in interferometry. Some of these works are in collaboration with Milano University and Insubria University. In particular, we are developing a quantum-enhanced holometer (i.e. a double Michelson interferometer aimed at testing quantum gravity) in collaboration with DTU.
11. From a theoretical point of view we worked on multidimensional QKD, application of mesons to local realism tests and quantification of quantum correlations (with Torino University, Politecnico and ISI).