At room temperatures the behavior of a gas of atoms is dominated by their random thermal motion. Averaged over time this gives simple descriptions in terms of thermodynamic variables such as Temperature and Pressure. As the temperature is lowered, this thermal motion is reduced. The Heisenberg uncertainty principle prevents the atoms from coming to a stop. Instead, at nanokelvin temperatures, quantum mechanics dictates the properties of these atomic gases. We study this strange and beautiful form of quantum matter. For some of our underlying motivations, please see essays written by individual group members:
Basic Physics of Cold GasesIt seems silly to write too much here. Instead we recommend that you look at some of the wonderful (interactive) essays on the subject which are already on the web:
ResourcesThese are a bit more technical, but are very useful.
- Ultracold Atom News: The site for all your ultracold atom information
- Center for Ultracold Atoms is a joint venture between MIT and Harvard. Has links to the home pages of almost all cold-gas researchers at MIT and Harvard.
- Istituto Nazionale per la Fisica della Materia Bose-Einstein Condensation in Trento Italy has a large concentration of theory on cold atoms.
- JILA [formerly the Joint Institute for Laboratory Astrophysics -- a collaboration between NIST (National Institute for Standards and Technology) and the University of Colorado)] has one of the highest concentrations of cold gas research in the country.
- Randy Hulet runs one of the premier cold atoms experimental groups from Rice University in Texas
Vortices and Topological Defects
Much of physics deals with the competition between order and disorder. Energetic typically drive matter towards an ordered state: the energy of a collection of sodium atoms is minized if it forms a crystal. On the other hand, energy is not the only concept playing a role in determining the behavior of a physical system. If you are at finite temperature, then entropy favors a disordered state. Similarly, at zero temperature "quantum fluctuations" may favor a disordered state. [For example, a classical crystal has every atom localized. A corrolory of the Heisenberg uncertainty principle is that it is hard to truly localize particles. Consequently you have materials such as Helium, which remain liquid down to arbitrarily low temperatures (at least at atmospheric pressure).]
Ordered states of matter typically have more degrees of freedom than unordered states: one would not notice if you uniformly translated all of the atoms in a liquid, but such a move would be important in a crystal. The object which encodes these degrees of freedom is the "order parameter". Order parameter textures occur when the order parameter varies slowly through space. A particularly interesting form of textures are those that are topological, meaning that they require the order parameter to be discontinuous. For example a dislocation in a crystal is topological.