Phd in PHYSICS

Thesis title: Hybrid Photonic Technologies for Quantum Information Tasks

In the last thirty years, Quantum Information has become an established research field, providing a unique framework to harness the properties of inherently quantum systems to process and transmit information in ways that surpass the capabilities of classical information processing. It has been shown how quantum-based approaches find several practical applications, such as quantum computing, simulation, metrology, and communication. In this context, thanks to continuous developments of photonic technologies, photon-based platforms have established themselves as an excellent experimental testbed for the demonstration and implementation of a wide range of Quantum Information Processing tasks. Within this framework, the main goal of the present Ph.D. thesis is to employ the toolbox of photon-based Quantum Information processing - together with the capabilities offered by a set of state-of-the-art photonic technologies related to photon generation, manipulation, and detection - to devise experimental platforms suitable for the demonstration of photon-based Quantum Information protocols. In this perspective, this work focused on developing a hybrid photonic architecture tailored for multiphoton Quantum Information experiments. I designed and assembled such a platform and characterized its underlying elements: Quantum Dot sources, time-to-spatial demultiplexing setups, and universal reconfigurable integrated photonic interferometers. This thesis's experimental results have been focused on the context of the characterization of multiphoton interference effects and the implementation of photon-based computational protocols. First, I experimentally investigated fully optical schemes suitable for the generation of polarization-based and orbital angular momentum-based entangled photon pairs via single photons emitted consecutively by a QD source. Then, given that the emergence of quantum interference effects in multiphoton scenarios is at the core of the concept of linear optical computing, I developed and validated, on one side, semi-device-independent techniques for characterizing multiphoton indistinguishability. On the other, I investigated the behavior of multiphoton interference effects in scenarios featuring partial distinguishability, where seemingly counterintuitive phenomena can arise. The last part of this Ph.D. thesis will be focused on the experimental realization of photon-based protocols related to quantum computing applications. I provided an experimental implementation of a hybrid quantum-classical technique that finds, via variational techniques, optimal linear optical circuits implementing a quantum cloning machine of dual-rail encoded qubits. Then, I considered a recently proposed routine for the manipulation of quantum randomness - the quantum-to-quantum Bernoulli Factory. I experimentally validated an architecture based on polarization-based encoding implementing such a protocol, exploiting the demultiplexed QD source interfaced with a fully in-bulk and modular interferometric setup. Finally, I employed the hybrid photonic architecture at its full capability to investigate a proof-of-principle photonic implementation of a so-called Adaptive Boson Sampling scheme, an approach that goes beyond the standard Boson Sampling paradigm via the addition of measurement-based adaptivity. Overall, the results reported here highlight the versatility of a hybrid photonic approach and may open the path toward increasingly complex demonstrations of photon-based platforms for Quantum Information tasks.