Tuning short- and long-range interactions in an ultracold chromium gas

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Ordered dipolar systems are well known, e.g. in the solid as ferromagnets and in the liquid phase as ferrofluids. Dipolar quantum gases are expected to exhibit a rich variety of new phenomena related to condensed matter physics and quantum optics. The goal of the proposed project is the creation and characterisation of degenerate bosonic and fermionic quantum gases using a dilute gas of chromium atoms. Due to the large magnetic moment of chromium, the dipole-dipole interaction plays an important role in this system. By cooling chromium down into the quantum degenerate regime, we will be able to observe the influence of the dipole-dipole interaction while so far only the effects of the s-wave contact interaction could be studied in e.g. rubidium or sodium Bose-Einstein condensates. Our system offers the possibility to change the dipole-dipole interaction by using time-varying magnetic fields and also the contact interaction by using Feshbach resonances. This allows us to independently control both interactions and to investigate their interplay on the properties of a quantum gas. We will investigate the dipolar order in the groundstate of bosonic and fermionic quantum degenerate gases. While the contact interaction is eqivalent to a Kerr nonlinearity in classical optics, which has lead to the observation of matter-wave solitons and vortices, there is no equivalent to the long-range interaction in classical optics. Thus, new phenomena are expected to emerge for a dipolar matter wave, which have no parallels in light optics. One example could be the generation of quantum correlations over a distance.