Conference Agenda

We report the experimental realization and characterization of quantum optical skyrmions exhibiting intrinsic topological robustness. By engineering structured photonic fields with tailored polarization–phase coupling, we generate skyrmionic configurations at the single-photon level and investigate their stability under controlled perturbations.

The demonstrated robustness originates from the nontrivial topology of the spin–orbit structured field, enabling protection against local distortions and modal crosstalk. We further analyze the role of structured light engineering in controlling the skyrmion topology, including polarization mapping, phase singularity manipulation, and mode superposition strategies.

Our results establish a direct bridge between classical structured light topology and quantum photonic states, opening new opportunities for robust information encoding and manipulation in the quantum regime. The presented framework is compatible with telecom-band implementations and metasurface-based platforms, providing a scalable route toward topologically protected quantum photonic systems.

Structured light beams with spatially varying polarization can be efficiently generated using voltage-tunable nematic liquid-crystal Q-plate. By selecting the appropriate input polarization and retardation, the resulting optical field develops a spatially structured polarization profile capable of encoding nontrivial topological information across the beam. This encoded topology can be directly probed through interaction with plasmonic nanostructures, such as circular and spiral slits. We show that, upon illumination, polarizationdependent excitation of surface plasmons transforms the hidden polarization topology into observable intensity patterns, including plasmonic vortices and distinctive interference features. Moreover, the tunability of the input parameters enables access to a wide range of topological configurations.

Orbital angular momentum (OAM)-entangled states produced by spontaneous parametric down-conversion (SPDC) are considered ideal for realizing high-dimensional entangled states, which have several advantages for quantum technologies. However, the limited sensitivity of current two-photon OAM detectors is a major roadblock not only for realizing such technologies but also for resolving foundational questions, such as OAM conservation in SPDC. The current theoretical understanding is that OAM is not conserved in Type-II SPDC but is conserved in Type-I. Experimentally, although non-conservation in Type-II has not been demonstrated, conservation in Type-I has been reported frequently and has become an underlying assumption for techniques generating high-dimensional OAM entangled states. In this work, we experimentally demonstrate a high-sensitivity two-photon OAM detector, using which, contrary to the current understanding, we report non-conservation of OAM in Type-I SPDC. We attribute this to a spatial walk-off effect and prove it using a framework free of standard phase-matching approximations.

Techniques to reconstruct the amplitude and phase of a light field allowed extended the sensing capabilities of optical devices, but these techniques normally rely on interferometry and therefore are limited to fully coherent light fields.

In this work, we implemented a technique for reconstructing photon number states in the classical optical domain to reconstruct the field Wigner function which contain all information about field correlation, not only amplitude and phase. The approach relies on the isomorphism between the paraxial wave equation and the quantum harmonic oscillator.

For pure states, that is, fully coherent states, we manage to experimentally reconstruct states with an accuracy above 95%, but the accuracy is reduced to 80% when considering partially coherent states.

The self-reconstruction of V-point polarization lattice structures (VPLS) is investigated. Polarization singularities arise where the parameters defining the polarization state of light become undefined and are classified as V-points or C-points. V-points exhibit spatially varying, predominantly linear polarization, and when arranged periodically, form a VPLS. In this work, the lattice is generated by superimposing four linearly polarized non-planar beams with precise alignment. The structure follows topological conservation, with radial and anti-radial V-points balancing each other. When partially obstructed, the lattice reconstructs itself after propagation, recovering both intensity and polarization, as confirmed by simulations. This self-healing occurs due to transverse energy flow induced by the non-zero transverse component of the Poynting vector. Unlike isolated V-points that split under perturbations, lattice V-points remain stable, highlighting the robustness of VPLS for applications in imaging, microscopic manipulation, and advanced beam shaping.