These ensembles do not exhibit an energy gap according to the Hugenholtz–Pines theorem, so the Hartree free particle does not correspond to a physically valid one although, like the bright and dark solitons, the Hartree free particle satisfies the Gross-Piatevskii equation, 
These ensembles do not exhibit an energy gap according to the Hugenholtz–Pines theorem, so the Hartree free particle does not correspond to a physically valid one although, like the bright and dark solitons, the Hartree free particle satisfies the Gross-Piatevskii equation, which governs these systems. These systems form when internal degrees of freedom decouple from reaction coordinates, a phenomenon known as Feshbach resonance, which leads to the formation of Tonks-Girardeau gasses in two-dimensional systems. The formation of one of these phases can be understood as the collapse of integer-spin particles into a single ground state. For ten points, name this form of matter first observed in laser-cooled rubidium.
These ensembles do not exhibit an energy gap according to the Hugenholtz–Pines theorem, so the Hartree free particle does not correspond to a physically valid one although, like the bright and dark solitons, the Hartree free particle satisfies the Gross-Piatevskii equation, which governs these systems.
{B}ose-{E}instein {c}ondensates (accept interacting {Bose gas}ses)