Structured light at small scales: customized nano-interactions for quantum cryptography and sensing

Light structured in amplitude, phase, and polarization offers new routes for encoding quantum information and probing matter at the nanoscale. We present two complementary approaches to harnessing structured-light–matter interactions for quantum technologies. First, we introduce an inversely designed vector beam decoder (VBD) that enables on-chip manipulation of non-paraxial modes with complex 3D polarization, expanding the Hilbert space for high-dimensional quantum key distribution (HD QKD) and integrated quantum photonic platforms. Second, we develop a theoretical framework for controlling multipolar excitations of a single nanoparticle using tightly focused Generalized Cylindrical Vector Beams (GCVBs). This approach allows selective excitation and suppression of dipolar and quadrupolar modes as well as their superpositions, offering tunable nanoscale control. Together, these advances establish structured light as a versatile tool for integrated quantum devices and precision sensing.