Perhaps the most striking feature of quantum mechanical theory is the fact that it predicts that matter can behave like waves. This means that coherent matter waves can form interference patterns, just like the ones you would get if you combined two laser beams in an interferometer. The demonstration of interfering pathways in a neutron interferometer was perhaps the strongest affirmation of quantum theory and the wavelike nature of matter. Atom interferometer experiments followed which extended this demonstration to the size of an entire atom. But these experiments were limited to showing that a single particle could interfere with itself. Now, Bose-Einstein condensation has allowed us to make another advance, making it possible to interfere two completely independent clouds of atoms with each other.

Interference of two Bose condensates was demonstrated for the first time in the month of November, 1996. This was done by cutting our atom trap in half with an argon-ion laser beam. We then cooled the sodium atoms in the two halves of the trap to form two independent Bose condensates. At this point, we quickly turned off the laser and the magnetic fields, allowing the atoms to fall and expand freely. As the two condensates began to overlap with one another, interference fringes formed such as the fringes in the images below.

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