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We realize a single particle microscope by using deterministically extracted laser-cooled ^{40}Ca^{+} ions from a Paul trap as probe particles for transmission imaging. We demonstrate focusing of the ions to a spot size of 5.8±1.0  nm and a minimum two-sample deviation of the beam position of 1.5 nm in the focal plane. The deterministic source, even when used in combination with an imperfect detector, gives rise to a fivefold increase in the signal-to-noise ratio as compared with conventional Poissonian sources. Gating of the detector signal by the extraction event suppresses dark counts by 6 orders of magnitude. We implement a Bayes experimental design approach to microscopy in order to maximize the gain in spatial information. We demonstrate this method by determining the position of a 1  μm circular hole structure to a precision of 2.7 nm using only 579 probe particles.

The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with Be + ions to less than P. Pérez et al.10 μK. The ultracold ions will then be photo-ionized just above threshold, and the free fall time over a known distance measured. We will describe the project, the accuracy that can be reached by standard techniques, and discuss a possible improvement to reduce the vertical velocity spread.

Compton scattering by the proton has been measured over a wide range covering photon energies 250 MeVEγ 800 MeV and photon scattering angles 30 • θ lab γ 150 • , using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The previously existing data base on proton Compton scattering is greatly enlarged by more than 700 new data points. The new data are interpreted in terms of dispersion theory based on the SAID-SM99K parametrization of photo-meson amplitudes. It is found that two-pion exchange in the t-channel is needed for a description of the data in the second resonance region. The data are well represented if this channel is modeled by a single pole with the mass parameter mσ ≈ 600 MeV. The asymptotic part of the spin dependent amplitude is found to be well represented by π 0 -exchange in the t-channel. No indications of additional effects were found. Using the mass parameter mσ of the two-pion exchange determined from the second resonance region and using the new global average for the difference of the electric and magnetic polarizabilities of the proton, α − β = (10.5 ± 0.9stat+syst ± 0.7 model ) × 10 −4 fm 3 , as obtained from a recent experiment on proton Compton scattering below pion photoproduction threshold, a backward spin-polarizability of γπ = (−37.1 ± 0.6stat+syst ± 3.0 model ) × 10 −4 fm 4 has been determined from data of the first resonance region below 455 MeV. This value is in a good agreement with predictions of dispersion relations and chiral perturbation theory. From a subset of data between 280 and 360 MeV the resonance pion-photoproduction amplitudes were evaluated leading to a E2/M1 multipole ratio of the p → ∆ radiative transition of EMR(340 MeV)= (−1.7±0.4stat+syst ±0.2 model )%. It was found that this number is dependent on the parameterization of photo-meson amplitudes. With the MAID2K parameterization an E2/M1 multipole ratio of EMR(340 MeV)= (−2.0 ± 0.4stat+syst ± 0.2 model )% is obtained.

Compton scattering by the proton has been measured over a wide range covering photon energies 250 MeV < ∼ E γ < ∼ 800 MeV and photon scattering angles 30 • < ∼ θ lab γ < ∼ 150 • , using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The data are in good agreement with the dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. From the subset of data between 280 and 360 MeV the resonance pion-photoproduction amplitudes were evaluated leading to the multipole E2/M1 ratio EMR(340 MeV) = (−1.6 ± 0.4 stat+syst ± 0.2 model )%. From all data below 455 MeV the proton's backward spin polarizability was determined to be γ π = (−37.9 ± 0.6 stat+syst ± 3.5 model ) × 10 −4 fm 4 .