What has dark energy to do with van der Waals forces? Why does the stress from van der Waals forces appear to violate Maxwell's equations? Why are ultracold atoms good candidates for testing this analog of dark energy? Find out in this paper.
The role of van der Waals forces in O((3)P)+H(2)(upsilon=1,j=0) collisions is investigated theoretically at low and ultralow temperatures. Quantum scattering calculations have been performed for zero total angular momentum using the lowest London-Eyring-Polanyi-Sato double-polynomial (3)A(") potential-energy surface reported by [Rogers et al., J. Phys. Chem. A 104, 2308 (2000)] and its recent BMS1 and BMS2 extensions developed by [Brandao et al., J. Chem. Phys. 121, 8861 (2004)] which provide a more accurate treatment of the van der Waals interaction. Our calculations show that van der Waals forces strongly influence chemical reactivity at ultracold translational energies. The presence of a zero-energy resonance for the BMS1 surface is found to enhance reactivity in the ultracold regime and shift the Wigner threshold to lower temperatures.
We consider the system of three 4He atoms to assess whether a pure van der Waals potential can be used as a starting point for an effective field theory to describe three-body processes in ultracold atomic systems. Using a long-range van der Waals interaction in combination with short-distance two-body counterterms, we analyze the dependence of two- and three-body observables on the short-distance regulator that is required due to the singular nature of the van der Waals interaction. We benchmark our approach with results obtained with the realistic $^{4}\mathrm{He}\ensuremath{-}^{4}\mathrm{He}$ LM2M2 potential and find good agreement. We furthermore show that in this effective field theory approach no three-body force is required at leading order and that universal van der Waals physics leads to a universal correlation between three-body observables in the absence of an Efimov three-body parameter.
Van der Waals interactions between ultracold atoms excited to high-lying Rydberg states can lead to \nstrongly correlated excitation dynamics [1]. In my talk I will present a direct observation in real space \nof the mechanical effect of the van der Waals force on individual Rydberg atoms excited at close range \n[2]. Clusters of Rydberg atoms are created by first generating a small number of seed excitations in a \nmagneto-optical trap, followed by off-resonant excitation that leads to a chain of facilitated excitation \nevents. Our experimental results agree well with a numerical simulation of the van der Waals explosion.