Collision-induced interactions of cold Rydberg atoms and the magnetic trapping of diamagnetic Rydberg atoms will be described. The effect of an excitation blockade on the statistics of the Rydberg-atom excitation number will also be discussed.
Systems of cold, interacting Rydberg atoms are of interest because they exhibit a wide range of collective quantum phenomena. This thesis describes experimental and theoretical work related to these systems with an emphasis on two phenomena: Rydberg excitation blockades and quantum-state-changing collisions. I begin by presenting a detailed calculation of the interaction energies of two Rydberg atoms for a variety of orientations, quantum states, and applied electric fields. The calculated energies are used to interpret the experimental results that follow. I then describe measurements showing that the widths of the distributions of Rydberg excitation number are related to the effectiveness of a Rydberg excitation blockade. These distributions are investigated as a function of principal quantum number, n, and applied electric field. In the presence of a Forster resonant field, sub-Poissonian distributions are measured. I next present a spectroscopic measurement of the energy level shift of a system of atoms which collectively shares two Rydberg excitations. The qualitative nature of the shift depends sensitively on the type of interactions between the atoms (van der Waals or dipole-dipole) and may be changed by changing the quantum state or applied electric field. This measurement provides the first spectroscopic proof that Rydberg excitation blockades are operative. Finally, I describe measurements of the probability for quantum state-changing and Penning-ionizing collisions to provide evidence for intrinsic, electric field-free-interaction resonances and complex many-body interactions in systems of cold Rydberg atoms.
We present an introductory review of the latest advancements cold Rydberg atom research. First, we briefly summarize the exaggerated properties of Rydberg atoms, and we discuss the new perspectives of Rydberg atom research that has been enabled by laser cooling and trapping technique. We then highlight the latest developments and achievements in the newly emerged research fields for Rydberg molecules and cold neutral plasmas. Various applications of the Rydberg blockade effect for quantum optics and quantum information science are also reviewed.
Abstract : Research on interactions between quantum gases and impurities has become an active area of AMO. Here, two setups have been constructed and operated towards these goals. In the first, a metal tip (diameter 125 microns) is mounted close to a magneto-optic trap (MOT). Rydberg excitations are implanted in a cold-atom region (diameter about 10 microns, length about 50 microns). Interactions between the excitations cause excitation blockades, short- and medium-range order, as well as dynamics due to van-der-Waals interaction. All these topics were studied. The second setup is a double-trap system, in which magnetically trapped rubidium atom samples are prepared between 1 and 10 micro-Kelvin temperature and densities of about 1012 cm-3. Cold circular Rydberg atoms have been prepared and trapped. The dynamics of these highly dipolar atoms in the magnetic trap was studied, and collision-induced loss was observed and traced back to collisions between the long-lived circular atoms and cold ground state atoms. Novel D-type molecules between Rydberg and ground-state atoms were realized. These molecules are due to an attractive triplet s-wave low-energy electron scattering interaction. Five papers were published [two Phys. Rev. Lett, 2 Phys. Rev. A] and one submitted to PRL.
Using electromagnetically induced transparency and photon storage, the strong dipolar interactions between Rydberg atoms and the resulting dipole blockade can be mapped onto light fields to realise optical non-linearities and interactions at the single photon level. We report on the realisation of an experimental apparatus designed to study interactions between single photons stored as Rydberg excitations in optically trapped microscopic ensembles of ultracold 87Rb atoms. A pair of in-vacuum high numerical aperture lenses focus excitation and trapping beams down to 1 μm, well below the Rydberg blockade. Thanks to efficient magneto-optical trap (MOT) loading from an atomic beam generated by a 2D MOT and the ability to recycle the microscopic ensembles more than 20000 times without significant atom loss, we achieve effective repetition rates exceeding 110 kHz to obtain good photon counting statistics on reasonable time scales. To demonstrate the functionality of the setup, we present evidence of strong photon interactions including saturation of photon storage and the retrieval of non-classical light. Using in-vacuum antennae operating at up to 40 GHz, we perform microwave spectroscopy on photons stored as Rydberg excitations and observe an interaction induced change in lineshape depending on the number of stored photons.