Experimental challenges in fullerene interferometry

Abstract

We discuss the experimental challenges in coherent matter wave optics with fullerenes. In particular, the properties of our matter wave source and the features of our eae cient, molecule-selective detector with high spatial resolution are presented. Their development was crucial for the successful recording of the molecular quantum interference patterns of individual molecules. Motivation of the experimentsThe fact that quantum mechanics possesses so many features which completely escape the perception of our everyday life is one of the remarkable properties of this theory. While the relative smallness ofh is frequently said to be responsible for the unobservability of quantum eå ects in the classical world, one may wonder whether there are limits to the theory or rather how far one can push the experimental techniques to test quantum mechanics. This question stimulated us to initiate a series of experiments in which we are trying to scale up the object size in quantum experiments [1]. An interesting testing ground in this respect are matter wave phenomena, i.e. the interference of a quantum object at a double slit or gratingÐ according to Feynman et al.[2] the prototype and paradigm for quantum mechanics.Young' s double slit experiment, ® rst described in 1807 [3] has always been regarded as a proof for the wave-like nature of light. However, things changed with the discovery of the photo-electric eå ect and the evident discrete nature of photons. Ever since then the two sides of the same quantum object appeared together: on the one hand the non-local wave nature needed to describe the unperturbed propagation and on the other hand the local aspect of the object when it is registered by the detector. Formally this corresponds to the superposition of various position states during propagation versus the projection into a position eigenstate in the measurement process.The ® rst experiment demonstrating quantum interference for such low intensities, where only single photons were present at a time, was performed by Taylor [4] in 1908. While this eå ect is already puzzling it becomes even stranger when massive particles are involved. Soon after de Broglie' s wave hypothesis for material particles [5] matter wave phenomena were experimentally veri® ed for electrons [6], atoms and dimers [7] and neutrons [8]. Young' s double slit experiment with matter waves was then performed by Mo È llenstedt and Jo È nsson for electrons [9], by Zeilinger et al. for neutrons [10], by Carnal and Mlynek for atoms [11] and by Scho È llkopf and Toennies for small molecules [12].

Numerical simulation of the double slit interference with ultracold atoms

“…2 Two-slit interference experiments have since been realized with massive objects, such as electrons, 3-6 neutrons, 7,8 cold neutrons, 9 atoms, 10 and more recently, with coherent ensembles of ultracold atoms, 11,12 and even with mesoscopic single quantum objects such as C 60 and C 70 . 13,14 This paper discusses a numerical simulation of an experiment with ultracold atoms realized in 1992 by F. Shimizu, K. Shimizu, and H. Takuma. 11 The first step of this atomic interference experiment consisted in immobilizing and cooling a set of neon atoms, mass mϭ3.349ϫ10 Ϫ26 kg, inside a magneto-optic trap.…”

Decoherence, Entanglement and Information Protection in Complex Quantum Systems

“…The counting background of 0.2 counts per second is solely due to electronic noise of the detector. Because of the tight focusing of the laser beam, the effective width of our detector [Nairz 2000] amounts to 8 µm, which is sufficient to resolve the individual diffraction orders. To record a diffraction pattern, we scan the laser across the molecular beam in steps of 2 µm.…”

“…The three gold gratings have a period of 990 nm, a nominal open fraction of 0.48 ± 0.02 (as specified by the manufacturer Heidenhain, Traunreut) and a flat open field of roughly 16 mm diameter. We limit the lateral width of the molecular beam to 1 mm which is also comparable to the width of the ionization range of the detecting laser beam [Nairz 2000]. The distance between consecutive gratings was set to L = 0.38 m. This corresponds to roughly twice the Talbot length and enables us to observe two Talbot recurrences (see Fig.…”

“…Following the most recent experimental data [Matt 1999] we assume that fragmentation is the least efficient mechanism. In contrast to that, thermally activated ionization is an important mechanism which we use both in our fullerene detector [Nairz 2000] and for molecule thermometry, as discussed below. Nevertheless, we can safely neglect both delayed ionization and fragmentation for the discussion of the fringe contrast since the recoil upon fragmentation and ionization is generally so large that the affected molecules will miss the narrow detector.…”

Double-slit interference with charged particles: density matrices and decoherence from time-dependent quantum Monte Carlo

“…Recently diffraction and interference effects have been observed experimentally with typical quantum objects like electrons and neutrons [1,2] as well as with mesoscopic objects such as C 60 [3] and C 70 [4]. The double-slit type of experiments which are among the simplest and most general quantum experiments have demonstrated undisputedly the significance of the information about the quantum states of a microscopic object which can be extracted from the interference patterns.…”