Usually, strongly attractive quantum gases are expected to form dense particle clusters and lose all gas-like properties.
But in 2005, it was proposed by Stefano Giorgini and co-workers that there is a many-body state of attractively interacting bosons that does not decay in one-dimensional systems.
Particles in a super-Tonks gas should be strongly correlated and show long range order with a Luttinger liquid parameter K<1.
Despite the mutual attraction, the single particle wave functions separate and the bosons behave similar to fermions with repulsive, long-range interaction.
Reducing the magnitude of the attractive interactions caused the gas to became unstable to collapse into cluster-like bound states.