Novel systems and techniques for the nonlinear optics at low light levels

This thesis describes novel experimental approaches to nonlinear optics at low light levels. These approaches focus on significantly increasing the probability of interaction between two weak pulses of light by using novel photonic systems and quantum control techniques. Specifically, the creation of a stationary pulse of light with non-vanishing photonic component was experimentally demonstrated. Our technique allows a pulse of light to enter into, be stopped inside, and finally be released from a room temperature coherently controlled atomic ensemble, which is dynamically and reversibly turned into a cavity-like system in the process. A detailed theoretical description of the phenomena is presented in addition to the experimental results that show pulses of light kept stationary for up to several microseconds. We also describe a technique for loading laser-cooled atoms into a single-mode hollow-core photonic-crystal fiber. In our approach, atoms collected in a magneto-optical trap are transferred into a dipole optical trap guided by such fiber. This trap confines the atoms inside the 7 µm diameter hollow core of this fiber for time scales on the order of tens of milliseconds. We observe atomic ensembles consisting of as few as 200 atoms creating an optically thick medium when confined inside the hollow-core fiber. We report the loading of up to 30000 rubidium atoms into this fiber, which results in a system with optical depth 150. Finally, we demonstrate a fiber-optical switch that is activated at tiny energies corresponding to a few hundred optical photons per pulse. This is achieved by simultaneously confining both photons and a small ensemble of cold atoms inside the microscopic hollow core of a single-mode photonic-crystal fiber and using techniques from quantum optics resulting in slow light propagation and large nonlinear interaction between light beams.