Lossless State Detection of Single Neutral Atoms

We introduce lossless state detection of trapped neutral atoms based on cavity-enhanced fluorescence. In an experiment with a single 87-Rb atom, a hyperfine-state-detection fidelity of 99.4% is achieved in 85 microseconds. The quantum bit is interrogated many hundreds of times without loss of the atom while a result is obtained in every readout attempt. The fidelity proves robust against atomic frequency shifts induced by the trapping potential. Our scheme does not require strong coupling between the atom and cavity and can be generalized to other systems with an optically accessible quantum bit.Comment: 4 pages, 4 figure

Generation of single photons from an atom-cavity system

A single rubidium atom trapped within a high-finesse optical cavity is an efficient source of single photons. We theoretically and experimentally study single-photon generation using a vacuum stimulated Raman adiabatic passage. We experimentally achieve photon generation efficiencies of up to 34% and 56% on the D1 and D2 line, respectively. Output coupling with 89% results in record-high efficiencies for single photons in one spatiotemporally well-defined propagating mode. We demonstrate that the observed generation efficiencies are constant in a wide range of applied pump laser powers and virtual level detunings. This allows for independent control over the frequency and wave packet envelope of the photons without loss in efficiency. In combination with the long trapping time of the atom in the cavity, our system constitutes a significant advancement toward an on-demand, highly efficient single-photon source for quantum information processing tasks.Comment: 7 pages, 5 figure

An Elementary Quantum Network of Single Atoms in Optical Cavities

Quantum networks are distributed quantum many-body systems with tailored topology and controlled information exchange. They are the backbone of distributed quantum computing architectures and quantum communication. Here we present a prototype of such a quantum network based on single atoms embedded in optical cavities. We show that atom-cavity systems form universal nodes capable of sending, receiving, storing and releasing photonic quantum information. Quantum connectivity between nodes is achieved in the conceptually most fundamental way: by the coherent exchange of a single photon. We demonstrate the faithful transfer of an atomic quantum state and the creation of entanglement between two identical nodes in independent laboratories. The created nonlocal state is manipulated by local qubit rotation. This efficient cavity-based approach to quantum networking is particularly promising as it offers a clear perspective for scalability, thus paving the way towards large-scale quantum networks and their applications.Comment: 8 pages, 5 figure

Electromagnetically Induced Transparency with Single Atoms in a Cavity

Optical nonlinearities offer unique possibilities for the control of light with light. A prominent example is electromagnetically induced transparency (EIT) where the transmission of a probe beam through an optically dense medium is manipulated by means of a control beam. Scaling such experiments into the quantum domain with one, or just a few particles of both light and matter will allow for the implementation of quantum computing protocols with atoms and photons or the realisation of strongly interacting photon gases exhibiting quantum phase transitions of light. Reaching these aims is challenging and requires an enhanced matter-light interaction as provided by cavity quantum electrodynamics (QED). Here we demonstrate EIT with a single atom quasi-permanently trapped inside a high-finesse optical cavity. The atom acts as a quantum-optical transistor with the ability to coherently control the transmission of light through the cavity. We furthermore investigate the scaling of EIT when the atom number is increased one by one. The measured spectra are in excellent agreement with a theoretical model. Merging EIT with cavity QED and single quanta of matter is likely to become the cornerstone for novel applications, e.g. the dynamic control of the photon statistics of propagating light fields or the engineering of Fock-state superpositions of flying light pulses.Comment: 6 pages, 4 figure

Probing the structure of methylalumoxane (MAO) by a combined chemical, spectroscopic, neutron scattering and computational approach

The composition of methylalumoxane (MAO) and its interaction with trimethylaluminum (TMA) have been investigated by a combination of chemical, spectroscopic, neutron scattering and computational methods. The interactions of MAO with donor molecules such as THF, pyridine and PPh3 as a means of quantifying the content of “free” and “bound” TMA have been evaluated, as well as the ability of MAO to produce [Me2AlL2]+ cations, a measure of the electrophilic component likely to be involved in the activation of single-site catalysts. THF, pyridine and diphenylphosphinopropane (dppp) give the corresponding TMA-donor ligand complexes accompanied by the formation of [Me2AlL2]+ cations. The results suggest that MAO contains not only Lewis acid sites but also structures capable of acting as sources of [AlMe2]+ cations. Another unique, but still unresolved, structural aspect of MAO is the nature of “bound” and “free” TMA. The addition of the donors OPPh3, PMe3 or PCy3 leads to the precipitation of polymeric MAO and shows that about that 1/4 of the total TMA content is bound to the MAO polymers. This conclusion was independently confirmed by pulsed field gradient spin echo (PFG-SE) NMR measurements which show fast and slow diffusion processes resulting from free and MAO-bound TMA, respectively. The hydrodynamic radius Rh of polymeric MAO in toluene solutions was found to be 12±0.3 Å, leading to an estimates for the average size of MAO polymers with about 50-60 Al atoms. Small angle neutron scattering (SANS) resulted in a radius RS = 12.0 ± 0.3 Å for MAO polymer, in excellent agreement with PFG-SE NMR experiments, a molecular weight of 1800 ± 100 g/mol and about 30 Al atoms per MAO polymer. The MAO structures capable of releasing [AlMe2]+ on reaction with a base were studied by quantum chemical calculations on MAO models (OAlMe)n(TMA)m for up to n = 8 and m = 5. Both –O−AlMe2−O− and –O−AlMe2−−Me− four-membered rings are about equally likely to lead to dissociation of [AlMe2]+ cations. The resulting MAO anions rearrange, with structures containing separated Al2O2 four-rings being particularly favourable. The results support the notion that catalyst activation by MAO can occur by both Lewis acidic cluster sites and [AlMe2]+ cation formation