Current research interests

I have worked in a wide area of fields from industrial software and electronics to space plasma physics to mathematical physics and non-commutative quantum field theory. This background reflects my broad spectrum of interests and experience.
Currently, the focus of my research lies on experimental physics on the nano-scale; more precisely, measurements of hydrodynamic forces and the Casimir effect. More generally, I am interested in vacuum energy and its consequences (see below).

Vacuum is, contrary to the common belief, not empty. Quantum field theory tells us that it is filled by an infinite number of virtual particles being created and annihilated again in an instant. These fluctuations are the cause of an – as well infinite – vacuum energy of the universe. Normally, we do not perceive this background since all of our everyday life happens relative to the vacuum energy level. In the presence of boundary conditions, as for example conductive objects at short separation, the frequency spectrum of the virtual particles is limited, so a part of the vacuum energy is removed – the space between the objects becomes `emptier’ than the surrounding vacuum. This results in a (mostly) attractive force between the boundaries, which is called the Casimir effect.

This interaction, however, is not purely abstract or hypothetical but can be measured and is even found in Nature. It has been shown that Geckos use the van der Waals force to crawl up smooth surfaces. Indeed, the Casimir and van der Waals forces can be interpreted to have the same origin, the difference being that the former typically acts between extended objects at distances up to a µm, while the latter names the interaction of (moelcular) dipoles at atomically small separations (up to a few nm).
Vacuum energy appears also in quantum field theory, where it causes divergences. These have to be removed by renormalizing the theory, which basically means to subtract the pure vacuum contribution in the absence of real interactions – essentially the same process which is necessary to obtain finite Casimir energies. It is not precisely known if vacuum energy exists physically, or if it is just a consequence of an incomplete description of the universe by our theories.

In the experiment, the Casimir effect has mainly been investigated by force measurements in the geometry of a sphere versus a plate, which prevents technical problems. However, some outstanding questions regarding the proper description of the dielectric function of metals and the contribution of non-zero temperature to the force require more accurate measurements to be answered. Currently, I am working on the design and construction of a new type of setup, which shall enable such measurements in the geometry of parallel plates, thereby allowing for a direct comparison of experiment and theory without assumptions or approximations. For more information see the CANNEX project page. Other projects regarding the Casimir effect concern the controlled variation of the force, and its often claimend influence on the operation of micro-electromechanic devices.

If the mean free path of fluid media (liquids and gases) is comparable to the size or extension of objects they are in contact with, then a phenomenon referred to as `slip' comes into play. This effect reduces the drag interaction between the fluid and the solid, and leads to flow patterns which are different from those expected from classical Stokes theory. Slip appears in ambient conditions at very small surface separations (sub-µm) in micro-mechanical and micro-fluidic devices, but also at low pressures at very high altitudes. For this reason, it is interesting for a wide range of fields from micro-machined sensors working with liquids to space flight. Despite a long history of dedicated research, the influence of various chemical and physical boundary parameters on slip are not completely understood.

Using an established atomic force microscope, I was able together with the group of Davide Iannuzzi to shed light on some of the influences the boundary properties have onto the formation of slip flow. Future experiments will focus on the influence of hydrodynamic forces on the operation of micro-electromechanic sensors.