Oriphiel

Well, temperature is just a way of gauging movement in particles (which creates friction, and summarily heat). So absolute zero was the lowest temperature thought possible, as everything ceased to move. But if there are particles than can keep moving beyond it, then the scale of temperature will expand to accommodate it.

Think about it like this: Imagine there's a field of grass that expands infinitely into the horizon. On the field, people run as far as they can, and then when they can't physically go any further they use some paint to mark down where they finished. Eventually, after hundreds of people have gone, nobody seems to be able to break a certain record set by someone who went before, who managed to go out really far. Everyone considers this to be the furthest that a human can possibly go, until someone proves that they can go further. But when someone does manage to go further, the limit that someone can possibly run is extended to the point where they collapsed. The field has an infinite distance to it, so technically the distance that humans can go is limitless, but there is still a definite point where almost everyone will have collapsed.

Temperature is the same way. Absolute zero was considered the mark in the grass that no substance could pass. Now that something has passed it, a new mark is set down, and the scale of possible temperature increases.

But i'm definitely no scientist, so I have no idea how they managed to do it. And I certainly know nothing about Quantum Mechanics.