BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d4aee2a94c0 DTSTART:20241115T093000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:Elements Room SUMMARY:ICFO | DANIEL GONCALVES ROMEU CLASS:PUBLIC DESCRIPTION:The rapid advancement of quantum technologies is currently push ing the boundaries of scientific and technological innovation. Among the v arious platforms for translating quantum theory into practical application s\, photons have emerged as particularly strong contenders. Their inherent advantages\, such as low decoherence and swift propagation\, make them id eal carriers of quantum information for communication\, computation and se nsing purposes. \;\nHowever\, the efficient manipulation and control o f photonic quantum states presents significant challenges\, often requirin g the use of interfaces. In this Thesis\, we investigate several novel app roaches to engineer and control the properties of light using a very tradi tional system: trapped neutral atoms in free space. \;\nIn Chapter 2\, we introduce a novel method to observe and manipulate strong quantum inte rference effects between a few photons and a single free-space atom. The a pproach uses a Maltese-cross configuration\, where two perpendicular pump and probe coherent fields drive the atom. Even for a weak atom-light coupl ing\, we demonstrate that adjusting the relative pump-probe strength ratio and phase can simulate an artificially enhanced coupling efficiency for s pecific observables. In particular\, we are able to engineer photon correl ations from fully anti-bunched to extremely bunched states\, and control t he linear transmission properties in specific directions.\nIn Chapter 3\, we propose the combination of ordered atomic arrays and Rydberg Electromag netically Induced Transparency (EIT) as a promising platform for quantum n onlinear optics. The spatial periodicity of the array enables precise cont rol over photon scattering\, reducing the inherent dissipation associated with traditional Rydberg EIT protocols. Using a two dimensional array\, we design and characterize a single photon switch\, where the storage of a s ingle photon as a Rydberg excitation results in a strong change in the sys tem's optical response. This switch can be used to implement a photon-phot on gate with an error scaling with the Rydberg blockade radius as Rb^{-4}\ , potentially reaching gate efficiencies of up to 99% for realistic experi mental parameters. Additionally\, we model the optical properties of the a rray in the strong driving regime\, where the system is multiply excited.\ nIn Chapter 4\, we discuss a recent experiment that observed features of t he Driven-dissipative Dicke phase transition in a driven elongated cloud i n free space. This is unexpected\, as the Dicke model typically involves a n ensemble coupling identically to a single\, lossy photonic mode\, akin t o an ensemble coupled to a cavity. Instead\, a free-space ensemble interac ts with a continuum of modes\, encoding propagation effects. Solving a sim ple model to explain this behavior\, based on the one-dimensional Maxwell- Bloch equations\, we observe nonanalytic behavior in certain observables. However\, a closer analysis reveals a significant spatial inhomogeneity in atomic properties. We thus argue that the free-space system does not unde rgo a phase transition but rather a &ldquo\;phase separation\,&rdquo\; rou ghly speaking\, between saturated and unsaturated regions. Beyond understa nding the phase transition\, we also elucidate under which conditions some properties of atoms in cavities can be mapped to atoms in free space.\nTo gether\, the results in this Thesis represent a meaningful contribution to wards better understanding phenomena associated to atom-light interactions in free space\, and towards translating that knowledge into practical use ful implementations.\n \;\nThesis Director: Prof. Dr. Darrick Chang DTSTAMP:20260407T071442Z END:VEVENT END:VCALENDAR