Control of ultracold quantum gases with shielded interactions

The BLUESHIELD project aims at joining the efforts of two French theoretical groups with complementary expertise in few-body (LAC-Orsay) and many-body (IPCMS-Strasbourg) quantum physics to design novel experimental ways to control the dynamics of ultracold quantum gases, which will be implemented by the Austrian partner (UIBK-Innsbruck). The central idea is the use of optical fields to dress quantum states of colliding ultracold atoms and molecules to prevent them to react at short distances. This optical shielding technique would allow the control of the competition between the various kinds of relevant interactions namely (i) short-range contact interactions, (ii) long-range, possibly anisotropic, light-modified interactions, and (iii) confinement by external magnetic or optical fields. At ultralow temperatures, novel many-body effects are expected to dominate and to produce new states of matter especially in reduced dimensions (lattice solids, Luttinger liquids). If successfully observed, these phenomena would have major impact for quantum simulation of condensed- matter Hamiltonians and for quantum information.

The research field of ultracold quantum gases has undergone a rapid development in the years since the creation of the first Bose-Einstein condensate in 1995. It has been found that ultracold atomic ensembles can be used for quantum simulation of highly correlated electronic systems, e.g. for electrons in a solid-state material. One hopes that with the help of ultracold gases novel materials with exotic properties such as high-temperature superconductivity can be simulated. Critical to many of the proposed experiments is the control of the interactions between the particles. On the one hand, one is interested in a strong elastic interaction, on the other hand, one wants to suppress inelastic scattering processes, which usually lead to particle loss and temperature increase. The aim of this project is to use laser light to control elastic and inelastic scattering processes. Theoretical support was provided by colleagues in France in Orsay and Strasbourg, the experiments were to be carried out in Innsbruck. Such control should be possible not only for atomic but also for molecular interactions. The range of possibilities would be greatly extended by the use of ultracold molecular system. The project has taken initial steps in this direction. However, a highlight of the project was a result that did not (yet) make use of the laser light control of the interaction: In a strongly interacting one-dimensional quantum gas, an effect could be observed that would otherwise only be expected for a crystalline system with a periodic structure (F. Meinert et al., Science 2017). An accelerated impurity showed periodic motion quite contrary to the expectation that the motion should simply be a drift of the particle. This experiment raises the exciting question of how strong elastic interactions generally influence the transport of particles in quantum wires. In view of the progressive miniaturization in the field of electronics, quantum wires will play a major role in the transport of particles in the future, and the present experiment addresses potentially relevant transport questions already now.