About the Bose-Einstein Condensate—A New State of Matter

We know about solids, liquids, gases, and plasmas —these are the well-known states of matter. But now there’s another, called the Bose-Einstein condensate (BEC), and it’s been predicted for a long time. In 1924, Albert Einstein built upon work of Satyendra Bose to predict that ultracold atoms could form a new state of matter, with all the atoms overlapping.

Physicist Deborah Jin of the National Institute for Standards and Technology (NIST) aligning an infrared laser in apparatus designed to create a Bose-Einstein Condensate of rubidium atoms (©Geoffrey Wheeler)

What does it mean to say that atoms overlap? The coins in a stack of pennies don’t overlap, and neither do the gas molecules in the air we breathe. As a gas becomes colder and colder, quantum mechanics tells us that the wavelike behavior of the atoms becomes more and more important. At the lowest temperatures—within a few hundred billionths of absolute zero—the probability waves of the atoms in a gas can overlap and create, in effect, one super-atom. In this state, it hardly even makes sense to talk about individual atoms because they all behave as one collective object. This is much like the output of a laser, since all the light is the same wavelength (same color) and the waves are all in step and you can’t tell one light particle (a photon) from another. In recent developments, BECs are being used to create atom lasers, the equivalent of a laser made of light.