We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry. © 2010 American Institute of Physics. ͓doi:10.1063/1.3499254͔Manipulation and control of electrically neutral particles, such as atoms and molecules in the gas phase is an active field of research. 1 The general aim is to increase the ability to control the motion of particles as they propagate in gas phase beams by means of deceleration, 2-5 trapping, 6 and cooling. 7,8 Today, cold atoms and small molecules are the best controlled physical systems and therefore are the ideal playground to study physics 9 and chemistry 10,11 at the most fundamental level. 12 For more complex systems-starting with molecules of more than about ten atoms-this level of control has not yet been achieved. Velocity selection is one of the first steps to increase control over the motion of large molecules and clusters. For instance, molecule interferometry is challenging today's gas phase manipulation technologies and will gain from improved beam monochromaticity: by reaching maximal interference visibility, 13 by higher precision in interferometric deflection for molecule metrology, 14 as well as by interferometric particle sorting. 15 Cooling and trapping of molecules will benefit from improved molecule velocity selection. 12 Plainly, our device can be used to select slow particles from a wide thermal velocity distribution 16 as proposed in one of the very early approaches to produce cold atoms. 17 As a further example, velocity selection can be used to separate buffer gas cooled molecules thermalized with their lighter coolant atoms propagating at much higher velocities. Furthermore, atom, molecule and cluster lithography techniques 18-20 will benefit from velocity pre-selected particles.We here have picked up the old idea to mechanically separate particles of different velocities, for instance generated by a thermal beam source with a very broad velocity distribution and base our design on earlier helical velocity selectors for neutrons, 21,22 atoms, 23 and the related slotted disk selectors for molecules. 24,25 The main idea is to make use of the difference in propagation time particles need for their passage through a spatial confinement. Such a confinement can be realized by a sequence slits arranged by rotating slotted disks at well defined positions and with well defined phase relations. It turns out ...

We report on the theoretical investigation of the Wigner distribution function (WDF) reconstruction of the motional quantum state of large molecules in de Broglie interference. de Broglie interference of fullerenes and the like already proves the wavelike behaviour of these heavy particles, while we aim to extract more quantitative information about the superposition quantum state in motion. We simulate the reconstruction of the WDF numerically based on an analytic probability distribution and investigate its properties by the variation of parameters which are relevant for the experiment. Even though the WDF described in the near-field experiment cannot be reconstructed completely, we observe negativity even in the partially reconstructed WDF. We further consider incoherent factors to simulate the experimental situation, such as a finite number of slits, collimation and particle-slit van der Waals interaction. From this we find experimental conditions to reconstruct the WDF from Talbot interference fringes in molecule Talbot-Lau interferometry.