Atom-trapping and photon-counting experiments with optical nanofibers

Abstract

New effects can arise in quantum physics when there is strong coupling, either between atoms and light or between different quantum systems. This thesis examines an optical nanofiber atom trap as a mediator of atom-light interactions and a potential element of a hybrid quantum system. The evanescent field around the sub-wavelength waist of an optical nanofiber possesses a small mode area that increases the cooperativity between atoms and the mode, in a manner analogous to traditional cavity QED. We demonstrate trapping of $^{87}$Rb atoms with an optical nanofiber, confining hundreds of atoms with typical trap lifetimes of tens of milliseconds. We then employ single photon counting techniques to study untrapped ensembles of cold atoms around the nanofiber. A first experiment uses intensity autocorrelations of resonance fluorescence emitted into the nanofiber mode to observe a transition from classical to nonclassical photon statistics. Measuring the correlations on longer timescales reveals the motion of atoms through the optical mode, and we develop a correspondence between the transit time and atomic cloud temperature. A second experiment measures Purcell enhancement of spontaneous emission of atoms near the nanofiber by correlating their fluorescence with a known trigger event. The spontaneous decay rate of an atom near a dielectric is modified by the induced dipole and by a change in the modes of the vacuum electromagnetic field. Our observed enhancement of $6.5\pm0.9%$ over the free-space rate matches well with what one finds from mode simulations in our system.