Long-lived state of ultracold bosons in the flat band of an optical kagome lattice

The kagome lattice hosts a flat band resulting from extensive geometric frustration. For fermions, this makes the kagome antiferromagnet a candidate for studying the quantum spin liquid phase. But even for weakly-interacting scalar bosons, the many-body physics in a flat band is complex and not fully understood. In this regime, condensation is dictated by quantum geometry and an exotic state with three-boson order (a "trion superfluid") is expected at intermediate temperatures. Stable loading of ultracold atoms into the flat band of an optical kagome lattice is challenging, as it is not the ground band. We achieve this for the first time by melting an attractive Mott insulator at negative absolute temperature. The state thus prepared occupies predominantly the flat band with a lifetime of many thousands of tunnelling times. It presents non-trivial structure in momentum space, so we use a variety of time-of-flight techniques to characterise it. I will report on our latest results.