Coherent Manipulation of Rydberg Polaritons

This thesis contains a statistical analysis of the resonant transmission of photons through an ensemble of cold Rubidium 87 atoms , where the resonant excited state is coupled to one or two highly-excited Rydberg states via optical and microwave fields. Transient emission with decay rates far below the excited state decay rate are observed. Analysis of the second-order auto-correlation statistic reveals Rydberg-mediated anti-bunching of transient photons, a signature of Rydberg blockade. The application of resonant microwave fields creates strong resonant interactions between Rydberg atoms. This presents a new, transient regime for the study of interaction-induced dephasing and blockade physics in cold atomic ensembles. A demonstration of a collective Rydberg qubit is presented. Quantum information is encoded into a superposition of Rydberg polariton states with a direct photonic interface suitable for applications in quantum networking. The coherence of Rydberg qubits is demonstrated through Ramsey interferometry. Sensitivity to AC and DC electric fields through differential Stark shifts of the qubit states is confirmed through a study of interferometric fringe shifts and dephasing. Controlled removal of atoms from the collective qubit under the action of a resonant scattering beam is shown to diminish readout fidelity but have little effect upon coherence due to the collective nature of the encoding. Theoretical models of the effect of photon scattering and electrical noise on the Rydberg qubit are confirmed experimentally. Ramsey fringe visibility is observed to scale with the fourth power of an applied noise field, matching a theoretical model.