Direct Observation of Sub-Poissonian Temporal Statistics in a Continuous Free-Electron Beam with Subpicosecond Resolution.

We present a novel method to measure the arrival time statistics of continuous electron beams with subpicosecond resolution, based on the combination of an rf deflection cavity and fast single electron imaging. We observe Poissonian statistics within time bins from 100 to 2 ns and increasingly pronounced sub-Poissonian statistics as the time bin decreases from 2 ps to 340 fs. This 2D streak camera, in principle, enables femtosecond-level arrival time measurements, paving the way to observing Pauli blocking effects in electron beams and thus serving as an essential diagnostic tool toward degenerate electron beam sources for free-electron quantum optics.

Observation of nonspreading wave packets in an imaginary potential.

We propose and experimentally demonstrate a method to prepare a nonspreading atomic wave packet. Our technique relies on a spatially modulated absorption constantly chiseling away from an initially broad de Broglie wave. The resulting contraction is balanced by dispersion due to Heisenberg's uncertainty principle. This quantum evolution results in the formation of a nonspreading wave packet of Gaussian form with a spatially quadratic phase. Experimentally, we confirm these predictions by observing the evolution of the momentum distribution. Moreover, by employing interferometric techniques, we measure the predicted quadratic phase across the wave packet. Nonspreading wave packets of this kind also exist in two space dimensions and we can control their amplitude and phase using optical elements.

Magnetic nanodots from atomic Fe: can it be done?

Laser focusing of Fe atoms offers the possibility of creating separate magnetic structures on a scale of 10 nm with exact periodicity. This can be done by using the parabolic minima of the potential generated by a standing light wave as focusing lenses. To achieve the desired 10-nm resolution, we need to suppress chromatic and spherical aberrations, as well as prevent structure broadening caused by the divergence of the incoming beam. Chromatic aberrations are suppressed by the development of a supersonic Fe beam source with speed ratio S = 11 +/- 1. This beam has an intensity of 3 x 10(15) atoms sr(-1) s(-1). The spherical aberrations of the standing light wave will be suppressed by aperturing with beam masks containing 100-nm slits at 744-nm intervals. The beam divergence can be reduced by application of laser cooling to reduce the transverse velocity. We have constructed a laser system capable of delivering over 500 mW of laser light at 372 nm, the wavelength of the (5)D(4) --> (5)F(5) atomic transition of (56)Fe we intend to use for laser cooling. Application of polarization spectroscopy to a hollow cathode discharge results in a locking system holding the laser continuously within 2 MHz of the desired frequency.