QUANTUM OPTICS OF SPIN-ORBIT PHENOMENA  

 

 quantum

Photons can be characterized by multiple physical properties (such as frequency, linear momentum, polarization, etc.) which can all be exploited to encode quantum information or to define quantum variables. Among them, we focus our attention on the orbital angular momentum (OAM), associated with the transverse spatial distribution of the optical field, and on the spin angular momentum (SAM), related to its polarization content. In quantum optics, using the SAM of single or multiple photons is a well established approach, while the idea of considering the OAM has become “popular” only in the last decade or so. The OAM can be used to encode high dimensional systems – or “qudits” – (its space is infinite dimensional!) and can be easily manipulated through standard photonic techniques. By the action of a device invented in our research group, the “q-plate”, a suitable interaction between the OAM and the SAM of a single photon can be engineered, eventually resulting in the entanglement of these two degrees of freedom. The application of this concept to different quantum scenarios, ranging from tests of the foundations of quantum mechanics to quantum simulations of different processes, represents the focus of our research activity.

SPIN-ORBIT INTERACTION IN LIGHT AND MATTER 

 qpl2


We are interested in studying optical phenomena involving the interaction of light and matter in which a coupling of the optical spin (or polarization) and the orbital degrees of freedom (the spatial distribution of the field) takes place. This may occur as a result of the medium being anisotropic and spatially structured in a prescribed way or of the input optical field itself being space-variant and suitably structured, or a combination of the two. The research activities within this line are mainly related to: (i) fabrication and characterization of novel liquid-crystal-based Pancharatnam-Berry optical elements, including q-plates (azimuthal waveplates with a topological singularity at their center), birefringent lenses and more complex wavefront modelers; (ii) methods and devices for detecting and measuring the spin and orbital angular momentum of light (SAM and OAM) or the optical topological charge; (iii) the exchange of angular momentum with anisotropic media, including in the case of nonlinear interactions; (iv) polarization-singular optics.

NONLINEAR SPECTROSCOPY AND STRUCTURED MATTER


spect 


We investigate various aspects of light-matter interaction by using ultrafast intense laser pulses, with particular emphasis on the case of hetero-structures and other spatially structured systems. Processes that are nonlinear in the optical field add new potentialities to standard optical spectroscopy, which has always been an invaluable experimental tool for elucidating fundamental mechanisms in condensed matter physics. For instance, by exploiting second-order processes (second harmonic generation - SHG, difference frequency generation – DFG, etc.) we investigate surface and interface properties with vertical sub-nanometer resolution or coherently generate single-cycle THz pulses, thus expanding our spectroscopic capability to the very-far infrared region. All these techniques may be implemented in a pump-probe scheme, allowing the investigation of the ultrafast dynamics of elementary excitations in materials. We have applied our spectroscopic tools to a large variety of materials with a special focus in recent years on the hetero-structures of transition-metal oxides, which exhibit unusual electronic properties due to strong electron-electron correlations. We are also interested in developing spatially structured ultrafast pulses and studying their interaction with matter.