"Unusual Thermodynamic Phenomena Observed in Quantum Systems"

Researchers in Germany and the US have created photon gases that can exist at “negative temperatures” while undergoing basic thermodynamic processes – including expansion and compression. The research could lead to the development of new optical technologies including those for data transmission. The team hopes to create negative temperature regimes in other degrees of freedom available to photons beyond their velocity: including space, frequency, and polarization.