In the area of quantum and nonlinear optics, mainly the topics related to generation, transmission, detection and quantum processing of information are treated, using the fields of photon pairs obtained by parametric downconversion as the main tool.
Several proposals of novel sources of photon pairs based on various photonic structures have been published, including randomly poled nonlinear crystals (Opt. Express 2010, 18, 27130), Bragg reflection waveguides (Opt. Express 2011, 19, 3115), ring-fibers (Opt. Express 2014, 22, 23743), or metal-dielectric structures (Phys. Rev. A 2014, 90, 043844). Such sources offer substantial advantages over traditional sources based on bulk nonlinear crystals, usable, e.g., in future metrological and quantum-information schemes. Besides higher compactness and better intensity-to-volume ratio, they may yield paired fields with extremely broad spectra, highly-dimensional entanglement, or pairs entangled in multiple quantities including orbital angular momentum. Some of the proposed sources have been experimentally constructed and tested. In this area works have been done in close cooperation with the Institute of Photonic Sciences, ICFO, Barcelona, Spain.
In the area of quantum information processing, main effort has been exerted on design and construction of elements for manipulation of quantum states based on linear optics. These include controlled phase gate (Phys. Rev. Lett. 2011, 106, 013602), entangling efficiency of quantum gates (Phys. Rev. A 2012, 86, 032321), cloning of quantum bits (Phys. Rev. A 2012, 85, 050307) and cloning-based eavesdropping on quantum channels (Phys. Rev. Lett. 2013, 110, 173601), quantum routing (Phys. Rev. A 2013, 87, 062333) and amplification of quantum bits (Phys. Rev. A 2013, 87, 012327). The effects of the environment on the transmission of quantum states have also been investigated (Phys. Rev. A 2012, 85, 063807). Most of these schemes have been experimentally realized in our laboratories. They may constitute elements of future quantum communication networks.
In the area of detection, approaches employing intensified CCD cameras have been developed to gain a general tool for investigation of photon-number, spatial and spectral correlations in the fields of photons pairs. These were used to investigate in detail the correlations of twin-photons from the process of parametric downconversion both at the single-photon level (Phys. Rev. A 2010, 81, 043827, Phys. Rev. A 2012, 85, 023816) and at the level of strong fields (Opt. Express 2014, 22, 13374). Using the photon-number entanglement, a method for calibration of quantum detection efficiency without the need of any radiation standard has been developed (Opt. Lett. 2012, 37, 2475) and later extended to detectors with analog output (Appl. Phys. Lett. 2014, 104, 041113) and to obtain the whole spectral calibration curve (J. Opt. Soc. Am. B 2014, 31, B1-B7). Efficient preparation of nonclassical states of light by postselection from photon pairs has also been presented (Opt. Express 2013, 21, 19387, Phys. Rev. A 2013, 88, 062304). Some of these works have been performed in cooperation with University of Insubria, Como, Italy.