Cluster Condensation and Symmetry-Protected Thermal Rigidity of Bose gases on the Haldane Sphere
We show that a spinless Bose gas on a Haldane sphere with a small monopole charge \(q\) realizes, in the lowest Landau level (LLL), an exactly solvable SU(2)-protected cluster condensate: a Hafnian condensate of two-boson singlets for \(q=1\), analogous to resonating-valence-bond singlet coverings, and a four-boson singlet condensate for \(q=3/2\). Unlike topologically protected quantum Hall states, the exactness of these states relies only on SU(2) symmetry and repulsiveness, with no pseudopotential fine-tuning. Their SU(2)-protected degeneracy renders the single-particle correlations exactly temperature-independent even as the clusters dissociate, a thermal rigidity absent in conventional Bose--Einstein condensates (BECs). Increasing the interaction drives a transition to a vortex BEC with spontaneously broken rotational symmetry.