Fig. 2. Experiment setup of the lateral Casimir force measurement

Fig. 3. SEM image of an imprinted grating on  the surface of the sphere.

Fig. 1. The measured lateral Casimir force at separation distance z=124.7 nm. The dots and solid line represent the data and theory, respectively. There are no fitting parameters between the experiment and the theory.

The lateral Casimir force

 

New theories that attempt at unifying all the fundamental forces predict the existence of extra dimensions and a host of new particles.  Both of these effects lead to deviations from Newtonian gravity.  For sub micron distance between two bodies, the Casimir force far exceeds the gravitational force.  Thus understanding the Casimir force is very important for checking the relevance of these unification theories. In this regard our precision measurements of the Casimir force have been used to set the strongest limits on the existence of new particles and extra dimensions in the 100 nm distance range.    

 

In 2009, we demonstrated  the asymmetry of the lateral Casimir force as shown in Figure 1 for the first time. The maximum of the lateral Casimir force is not at the middle of two adjacent minima. The data is in excellent agreement with the recently developed scattering theory for the lateral Casimir force.  The experiment setup was improved as shown in Figure 2 and a SEM image of the imprinted corrugation on the sphere is shown in Figure 3.

In 2002, we extended our earlier work on shape dependent Casimir Forces by performing the first experimental demonstration of the lateral Casimir forces which acts parallel to the two surfaces used. This was the first experimental observation of an effect that was theoretically predicted in 1997.

 

We demonstrated it between two aligned surfaces, imprinted with nanoscale sinusoidal corrugations. The need to imprint aligned nanoscale corrugations makes the experiment extremely difficult (crossover of axis leads to zero force). The lateral Casimir force measured was about a few hundred femto Newtons (10^-13 N). This spurred theoretical predictions on the role of diffraction like coherent scattering of zero point photons from the periodic corrugations. After six years of experimentation we finally succeeded in demonstrating these coherent zero point effects in the lateral force. They required the use of aligned corrugations on the same scale as the separation distance of between 120-170 nm.  Note that the Casimir force decreases rapidly with distance and therefore small corrugation periods are required for the demonstration.  The lateral Casimir force, is now recognized to have strong potential to bring about non contact motion in nanoscale gears, ratchets and pinions, which would otherwise be impossible due to abrasion from contact.