Dottorato in MODELLI MATEMATICI PER L'INGEGNERIA, ELETTROMAGNETISMO E
NANOSCIENZE

Titolo della tesi: Strain engineering low-dimensional excitons: a building block for nanotechnology

Low-dimensional semiconductors represent a fascinating platform for advancing future nanotechnology. In particular, two-dimensional Transition Metal Dichalcogenides (TMDs) have gained significant attention following the discovery of graphene. These materials offer unique physical properties such as strong spin-orbit coupling, valley-selective optical selection rules, and high tolerance to mechanical deformation. Additionally, their out-of-plane confinement results in dominant 2D-excitonic features, making them ideal for nanoscale device fabrication. When carriers are confined beyond the 2D limit, the energy levels of zero-dimensional excitons become discrete, leading to the emission of individual light quanta. This phenomenon is observed in TMDs and GaAs quantum dots (QDs), semiconductor nanostructures embedded in a wider energy-gap material that can emit single and entangled photons on demand. These 0D-excitons are pivotal for the second quantum revolution, which aims to exploit quantum mechanics for secure communication, enhanced computational power, and single-particle sensing. This thesis presents our recent progress in strain engineering low-dimensional excitons. We investigate the properties of 2D excitons in TMDs experiencing large deformation fields using patterned substrates and low-energy proton irradiation. Our findings reveal that high-anisotropic uniaxial strain fields enhance photoluminescence and allow for the observation of room-temperature linear polarization. Beyond 2D-excitons, we explore 0D-excitons in TMDs and GaAs QDs. Using micromachined piezoelectric actuators, we dynamically induce strain, achieving significant energy and brightness tuning for QDs in TMDs. Furthermore, we demonstrate advanced quantum protocols with strain-engineered 0D-excitons in GaAs QDs, utilizing dynamic strain tuning to restore the entanglement. This technical tool enables quantum key distribution and quantum state teleportation over three nodes in a free-space channel, paving the way for the future quantum network.