Detection of quantum entanglement in physical systems

Quantum entanglement is a fundamental concept both in quantum mechanics and in quantum information science. It encapsulates the shift in paradigm, for the description of the physical reality, brought by quantum physics. It has therefore been a key element in the debates surrounding the foundations of quantum theory. Entanglement is also a physical resource of great practical importance, instrumental in the computational advantages offered by quantum information processors. However, the properties of entanglement are still to be completely understood. In particular, the development of methods to efficiently identify entangled states, both theoretically and experimentally, has proved to be very challenging. This dissertation addresses this topic by investigating the detection of entanglement in physical systems. Multipartite interferometry is used as a tool to directly estimate nonlinear properties of quantum states. A quantum network where a qubit undergoes single-particle interferometry and acts as a control on a swap operation between k copies of the quantum state ρ is presented. This network is then extended to a more general quantum information scenario, known as LOCC. This scenario considers two distant parties A and B that share several copies of a given bipartite quantum state. The construction of entanglement criteria based on nonlinear properties of quantum states is investigated. A method to implement these criteria in a simple, experimentally feasible way is presented. The method is based of particle statistics’ effects and its extension to the detection of multipartite entanglement is analyzed. Finally, the experimental realization of the nonlinear entanglement test in photonic systems is investigated. The realistic experimental scenario where the source of entangled photons is imperfect is analyzed.