Integrated Calendar

What form of matter can be simpler than a dilute gas of particles? The cases of non-interacting and weakly interacting particles are well understood. So what happens if the interactions get stronger? Depending on the interactions this will lead to a vast variety of materials with strong correlations. Simple models assume short range (delta function like) attractive or repulsive interactions.
Such systems can be realized with ultracold atoms, using the tools of atomic physics. We have studied a gas of ultracold fermions with both attractive and repulsive interactions. Fermions with attractive interactions undergo a phase transition to superfluidity. This is the simplest system which captures the essence of existing superconductors, but also extends to regimes where the transition temperature is very high. For repulsive interactions, a transition to a ferromagnetic phase has been predicted, but our experiments have shown that such a transition does not take place.
This illustrates the role of ultracold atoms as quantum simulators of seemingly simple Hamiltonians, for which no reliable solutions have been found computationally.

The behavior of hydrogen molecules inside nanoscale cavities of diverse host materials, e.g., fullerenes, carbon nanotubes, clathrate hydrates, and metal-organic frameworks, has received a great deal of attention in recent years. Much of the research has been driven by the potential which some of these systems have for hydrogen storage applications. In nanoscale confinement, the translational motions of the caged molecules are quantized and strongly coupled to the molecular rotations, which are also quantized. I will review our rigorous quantum treatment of the intricate coupled translation-rotation (TR) dynamics of the caged H2/HD/D2, their dependence on the symmetry of the nanocavity, and the distinct spectroscopic signatures of the TR coupling that we have identified. These TR eigenstates are directly probed by the inelastic neutron scattering spectroscopy (INS). I will also present our recently developed methodology for accurate quantum simulation of the INS spectra of a hydrogen molecule in a nanocavity of an arbitrary shape, its implementation to H2/HD in clathrate hydrates and C60, and comparison with the measured INS spectra. At the end, a new and unexpected selection rule that we have derived for the INS spectroscopy of H2/HD in a near-spherical cage such as C60 will be briefly discussed. It explains why the INS transitions between certain TR eigenstates of H2/HD in C60 have zero intensity and do not appear in the spectra.