A system with negative thermodynamic temperature is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system.

This situation occurs because temperature is not really a measure of speed of particles, but rather a measure of entropy, and for ordinary objects entropy can increase infinitely, increasing temperature too. For systems with capped amount of states entropy reduces when energy is added, and that is negative thermodynamic temperature.

So negative temperature is more energetic than positive, and because of that it heats up positive temperature object when in contact.

Light kinda does that, but I am not sure I can come up with an explanation of how to measure its temperature and if it fits the definition