We use a single-ion electric-field noise sensor in combination with in situ surface treatment and analysis tools, to investigate the relationship between electric-field noise from metal surfaces in vacuum and the composition of the surface. These experiments are performed in a setup that integrates ion trapping capabilities with surface analysis tools. We find that treatment of an aluminum-copper surface with energetic argon ions significantly reduces the level of room-temperature electric-field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The noise levels after treatment are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap at room temperature.

We report the enhancement of the radiative decay rate of Eu 3+ fluorophores by coupling them to nanoscopic gold disks located on a substrate. When the plasmon resonance frequency of the disks coincides with the fluorophore emission frequency, each disk acts as a supplemental antenna for the fluorophore by converting its nonradiative near field into radiating far field, thereby increasing its radiative decay rate dramatically. The radiative rate is measured by time-correlated single-photon counting for resonant and nonresonant metallic nanodisks. Supplementary theoretical model calculations are found to be in remarkably good agreement with the experiment.

In this letter, we report an absorption spectroscopy experiment and the observation of electromagnetically induced transparency from a single trapped atom. We focus a weak and narrowband Gaussian light beam onto an optically cooled 138 Ba + ion using a high numerical aperture lens. Extinction of this beam is observed with measured values of up to 1.3%. We demonstrate electromagnetically induced transparency of the ion by tuning a strong control beam over a two-photon resonance in a three-level Λ-type system. The probe beam extinction is inhibited by more than 75% due to population trapping.PACS numbers: 42.50. Gy, Atom-photon interfaces will be essential building blocks in future quantum networks [1,2]. Here, photons are usually adopted as the messengers due to their robustness in preserving quantum information during propagation, while atoms are used to store the information in stationary nodes. The efficient transfer of quantum information between atoms and photons is then essential and requires controlled photon absorption with a very high probability. The requisite strong coupling can be achieved, for example, using high finesse cavities [3][4][5] or large atomic ensembles [6,7], which are the most studied routes towards such goals.Coupling of radiation to a single atom in free space is generally considered to be weak, however, technological advances, as nowadays available with large aperture lenses [8] and mirrors [9], recently led to reconsider this point of view. Novel experiments demonstrated extinctions of about 10% from single Rubidium atoms [10], single molecules [11,12] and quantum dots [13]. More recently, a light phase shift of one degree was observed by tuning an off-resonant laser to a single Rubidium atom [14], and non-linear switching was demonstrated with a single molecule [15]. These experiments demonstrate first steps towards quantum optical logic gates and quantum memories with single atoms in free space.Long term and controlled storage of quantum information will likely require electromagnetically induced transparency (EIT). This technique is widely used to control the absorption of weak light pulses or single photons in atomic ensembles [7,16] and in high-finesse cavities [17]. Here, a two-photon Raman transition in lambda-type three-level atoms is driven by the weak probe light together with a strong control laser. The control laser leads to splitting of the excited state by the AC Stark effect, which suppresses the absorption of the resonant probe light. Consequently, the change of the control laser intensity can gate the propagating probe field between absorption and transmission. Furthermore, adiabatic switching of the control light can trigger the storage and retrieval of a probe photon onto and from the long-lived atomic ground states [1,18].So far, EIT has been a phenomenon specific to optically thick media consisting of ensembles of many atoms [18], where both the optical fields and the atomic states are modified. However, quantum information processing requires single well-define...

We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.

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