  We investigate $B \bar B$ systems by computing potentials of two static
quarks in the presence of two quarks of finite mass using lattice QCD. By
solving the Schr\"odinger equation we check whether these potentials are
sufficiently attractive to host bound states. Particular focus is put on the
experimentally most promising bottomonium-like tetraquark candidate $Z_b^\pm$
with quantum numbers $I(J^P)=1(1^+)$.
