Superfluidity at negative temperatures: Bosons with tunable interactions in an optical lattice

Ulrich Schneider

In a system where the Hamiltonian is bounded from above - that is where there exists a highest energy state - the usual thermodynamics can be extended to include negative absolute temperatures (T<0). I will show how these states can be realized using ultracold atoms in optical lattices and will present our recent observation of bosonic superfluidity at T<0.