Entanglement enhanced communication and sensing

Entanglement has been an extremely active field of research both from a theoretical and an experimental point of view. As the understanding of the phenomena grows, so does the interest in using it to advance different technological fields: communica- tion, computing and sensing being just some examples. It is now well known that entangled photon pairs can be generated through a process known as spontaneous parametric down-conversion (SPDC). In this thesis I therefore integrate the SPDC generated photons in a variety of experiments each exploiting a different charac- teristic of this quantum effect. In particular, both chapter 3 and chapter 4 utilise the spatial degree of freedom of SPDC generated entangled photons to enhance the quantity of information that can be transmitted in quantum communication systems. In particular, in chapter 3 the information capacity of two of the best known spa- tial modal sets is analysed in the context of real life finite-aperture communication systems, while chapter 4 proposed a new approach for imparting information onto photons. On the other hand, both chapters 5, and 6 rely on the ability of SPDC to generate completely indistinguishable photon pairs, which, when made to interfere, bunch together in what is known as N00N state. In particular, chapter 5 demon- strates that the recently discovered “Coherent Perfect Absorption” process (CPA) can be used to coherently control and absorb two-photon N00N states and therefore can be employed in the generation of quantum gates, while in chapter 6, the quantum interference process that produces the N00N states is used to test the role of relativity in quantum mechanics through the construction of a “quantum gyroscope”.