With quick skim there seems to be nothing new here. It is negative temperature they speak of. In any system with energy levels the population of higher states is normally less than the lower state populations. (Assuming number of degenerate levels of the upper state is not greater.) The same level populations equations as function of temperature require a negative temperature, when this is not the case - more populated upper state. This is the condition in ALL lasers. Lasers can be consider to be "negative temperature devices." Some "pumping mechanism" is required to maintain this inverted population or "negative temperature." That is all article seems to be telling, but that has been long known.
