Andreas Koglbauer

Experimental Demonstration of Single-Site Addressability in a Two-Dimensional Optical Lattice

We demonstrate single-site addressability in a two-dimensional optical lattice with 600 nm lattice spacing. After loading a Bose-Einstein condensate in the lattice potential, we use a focused electron beam to remove atoms from selected sites. The patterned structure is subsequently imaged by means of scanning electron microscopy. This technique allows one to create arbitrary patterns of mesoscopic atomic ensembles. We find that the patterns are remarkably stable against tunneling diffusion. Such microengineered quantum gases are a versatile resource for applications in quantum simulation, quantum optics, and quantum information processing with neutral atoms.

A continuous wave 10 W cryogenic fiber amplifier at 1015 nm and frequency quadrupling to 254 nm

A stable, continuous wave, single frequency fiber amplifier system at 1015 nm with 10 W output power is presented. It is based on a large mode double clad fiber cooled to liquid nitrogen temperature. The amplified light is frequency quadrupled to 254 nm and used for spectroscopy of the 6¹S → 6³P transition in mercury.

Probing Bose-Einstein condensates by electron impact ionization

We describe an experiment that allows for the study of ultracold quantum gases by electron impact ionization. The setup combines a scanning electron microscope and an apparatus for the production of Bose-Einstein condensates of rubidium atoms. With a diameter as small as 50 nm, the electron beam locally interacts with the much larger condensate. The produced ions are used to probe the many-body system with single atom sensitivity. We discuss the general scheme of this technique with special emphasis on the technical equipment and on the specific phenomenology of the particular collisional system.

ac-Stark shift and photoionization of Rydberg atoms in an optical dipole trap

We have measured the ac-Stark shift of the 14D5/2 Rydberg state of rubidium 87 in an optical dipole trap formed by a focused CO2 laser. We found good quantitative agreement of the result with the model of a free electron experiencing a ponderomotive potential in the light field. In order to reproduce the observed spectra, we take into account the broadening of the Rydberg state due to photoionization. The extracted cross section is compatible with previous measurements on neighboring Rydberg states.

A semiconductor laser system for the production of antihydrogen

Laser-controlled charge exchange is a promising method for producing cold antihydrogen. Caesium atoms in Rydberg states collide with positrons and create positronium. These positronium atoms then interact with antiprotons, forming antihydrogen. Laser excitation of the caesium atoms is essential to increase the cross section of the charge-exchange collisions. This method was demonstrated in 2004 by the ATRAP collaboration by using an available copper vapour laser. For a second generation of charge-exchange experiments we have designed a new semiconductor laser system that features several improvements compared to the copper vapour laser. We describe this new laser system and show the results from the excitation of caesium atoms to Rydberg states within the strong magnetic fields in the ATRAP apparatus.

Continuous-wave spontaneous lasing in mercury pumped by resonant two-photon absorption

We demonstrate the first cw two-photon absorption laser-induced stimulated emission. The 7(1)S(0)-6(1)P(1) transition in mercury at a 1014 nm wavelength is used, and selective lasing of different isotopes is observed.

A reliable cw Lyman-α laser source for future cooling of antihydrogen

We demonstrate a reliable continuous-wave (cw) laser source at the 1 S–2 P transition in (anti)hydrogen at 121.56 nm (Lyman-α) based on four-wave sum-frequency mixing in mercury. A two-photon resonance in the four-wave mixing scheme is essential for a powerful cw Lyman-α source and is well investigated.

Triple resonant four-wave mixing: A microwatt continuous-wave laser source in the vacuum ultraviolet region at 120 nm

We present a vacuum ultraviolet laser source by four-wave mixing in mercury vapour based on solid-state laser systems. Maximum powers of 6μW were achieved with an increase of four orders of magnitude in efficiency.