Analysis of a single-atom dipole trap

We describe a simple experimental technique which allows to store a single Rubidium 87 atom in an optical dipole trap. Due to light-induced two-body collisions during the loading stage of the trap the maximum number of captured atoms is locked to one. This collisional blockade effect is confirmed by the observation of photon anti-bunching in the detected fluorescence light. The spectral properties of single photons emitted by the atom were studied with a narrow-band scanning cavity. We find that the atomic fluorescence spectrum is dominated by the spectral width of the exciting laser light field. In addition we observe a spectral broadening of the atomic fluorescence light due to the Doppler effect. This allows us to determine the mean kinetic energy of the trapped atom corresponding to a temperature of 105 micro Kelvin. This simple single-atom trap is the key element for the generation of atom-photon entanglement required for future applications in quantum communication and a first loophole-free test of Bell's inequality.Comment: Version 2; formula in equ. 3 correcte

Linear Optics C-Phase gate made simple

Linear optics quantum logic gates are the best tool to generate multi-photon entanglement. Simplifying a recent approach [Phys. Rev. A 65, 062324; Phys. Rev. A 66, 024308] we were able to implement the conditional phase gate with only one second order interference at a polarization dependent beam splitter, thereby significantly increasing its stability. The improved quality of the gate is evaluated by analysing its entangling capability and by performing full process tomography. The achieved results ensure that this device is well suited for implementation in various multi photon quantum information protocols.Comment: 5 pages, 4 figure

Highly-efficient state-selective sub-microsecond photoionization detection of single atoms

We experimentally demonstrate a detection scheme suitable for state analysis of single optically trapped atoms in less than 1 {\mu}s with an overall detection efficiency {\eta} exceeding 98%. The method is based on hyperfine-state-selective photoionization and subsequent registration of the correlated photoion-electron pairs by coincidence counting via two opposing channel electron multipliers. The scheme enables the calibration of absolute detection efficiencies and might be a key ingredient for future quantum information applications or precision spectroscopy of ultracold atoms.Comment: 4 pages, 4 figure

Ascertaining the Values of σx\sigma_x, σy\sigma_y, and σz\sigma_z of a Polarization Qubit

In the 1987 spin retrodiction puzzle of Vaidman, Aharonov, and Albert one is challenged to ascertain the values of $\sigma_x$, $\sigma_y$, and $\sigma_z$ of a spin-1/2 particle by utilizing entanglement. We report the experimental realization of a quantum-optical version in which the outcome of an intermediate polarization projection is inferred by exploiting single-photon two-qubit quantum gates. The experimental success probability is consistently above the 90.2% threshold of the optimal one-qubit strategy, with an average success probability of 95.6%.Comment: 4 pages, 2 figures; final version with new title and new abstract; to appear in Physical Review Letter

Zur Verwertbarkeit der Grossschreibung bei der automatischen Reduktion syntaktischer Wortformen-Mehrdeutigkeiten im Deutschen

Diese zusammen mit Heinz-Josef Weber erstellte Studie zeigte, dass die Bedeutung der Groß-/Klein-Schreibung für die Reduktion von syntaktischen Mehrdeutigkeiten nicht so groß ist, wie vorher angenommen. Dies hat nicht nur für die automatische Analyse, sondern auch für die Diskussion über eine (gemäßigte) Rechtschreibreform Relevanz

Comparing perceived effects of climate-related environmental change and adaptation strategies for the Pacific small island states of Tuvalu, Samoa, and Tonga

Inhabitants of Pacific small island states are facing multiple socio-ecological pressures, with climate change being one of the most prominent. Nevertheless, the agency of local stakeholders in decisions on how to adapt to climate-related environmental change has been largely underappreciated in the climate change sciences as well as in policy decisions. We, therefore, conducted a survey study in Tuvalu, Samoa, and Tonga, asking specifically how residents perceive their situation regarding climate-related challenges, what adaptation strategies they have devised and implemented, and what they expect of governmental and nongovernmental organisations in these efforts. In contrast to the common perception that Pacific small island states are primarily threatened by rising sea levels, residents’ perceptions indicate that drought, cyclones and other flood-related problems pose a far more imminent danger. Our results suggest that further research on those perceived environmental changes is advisable to provide reliable data for scientific models and policy decisions

Towards a loophole-free test of Bell's inequality with entangled pairs of neutral atoms

Experimental tests of Bell's inequality allow to distinguish quantum mechanics from local hidden variable theories. Such tests are performed by measuring correlations of two entangled particles (e.g. polarization of photons or spins of atoms). In order to constitute conclusive evidence, two conditions have to be satisfied. First, strict separation of the measurement events in the sense of special relativity is required ("locality loophole"). Second, almost all entangled pairs have to be detected (for particles in a maximally entangled state the required detector efficiency is 82.8%), which is hard to achieve experimentally ("detection loophole"). By using the recently demonstrated entanglement between single trapped atoms and single photons it becomes possible to entangle two atoms at a large distance via entanglement swapping. Combining the high detection efficiency achieved with atoms with the space-like separation of the atomic state detection events, both loopholes can be closed within the same experiment. In this paper we present estimations based on current experimental achievements which show that such an experiment is feasible in future.Comment: 6 pages, 3 figures, to be published in Advanced Science Letter