It is hard to overestimate the influence quantum-mechanics has on the way the universe works. Everything, you, me, your ipod, are all made up out of atoms, and these atoms obey quantum mechanical laws. These laws appear very strange and to have no relation to the “real” world. However, big things are made up out of little things, and these little things are quantum-mechanical. So by studying quantum-mechanics, we find out how things really work.
A basic premise in QM is the Heisenberg uncertainty principle, which states that you can not know the position and the momentum of a particle with infinite precision at the same time. In fact, the uncertainty in momentum times the uncertainty in position has to be larger than some value, which is Planck’s constant. Hence, if you know the velocity with infinite precision, the uncertainty in position will have to be infinite.
Now Planck’s constant is a pretty small number, and in everyday life we don’t really notice anything being uncertain. What we are investigating is how you build a classical, everyday world from the laws of quantum-mechanics. One of the steps in this direction is to create a large system that still only obeys quantum mechanics: this is a Bose-Einstein condensate.
Now what is a Bose-Einstein condensate? The temperature of atoms is associated with their motion, the lower the temperature, the slower the atoms move. The lowest possible temperature is therefore the point that atoms don’t move at all, which is absolute zero, or about -273 degrees C.
Now quantum mechanics has a problem with atoms not moving at all, which is based on the Heisenberg Uncertainty principle: if their velocity is zero, it it infinitely well defined, and according to the Uncertainty principle these atoms should exist everywhere in the universe at once.
So there is a limit to the lowest possible temperature, which is determined by the size of the box you lock these atoms in. In a box the velocity of the atoms is quantised, i.e., it can only take on certain values. One of these is the slowest possible. In my setup, we get about 100,000 atoms to occupy just that value. This constitutes a Bose-Einstein Condensate (BEC), which was predicted by Einstein, and seen for the first time in 1995 by some groups in the USA, who got the 2001 Nobel prize for their research.
Nowadays, this has grown into a very active field of research. My group is the first (and only) in the southern hemisphere to have achieved a BEC through purely optical means.
A BEC is a new state of matter, that does not exist anywhere in the universe except in research labs. As such, it provides a fascinating field of research at the forefront of science.
The study of BECs has already transformed our understanding of such phenomena as superconductivity and superfluidity. But mostly, it allows scientists to study quantum features in a large(ish) system, and from there increase our knowledge of quantum-mechanics, and how you and me are really put together.