Atom Laser

What is the physical meaning of Bose-Einstein condensation? How to cut a cloud of atoms in two? How to use coherence in large atomic systems to create quantum computers? These and other questions are answered by Massachusetts Institute of Technology Lester Wolfe Professor of Physics, Daniel Kleppner.

A laser is a device in which atoms or other entities radiate by stimulated emission into a single radiation field which produces intense radiation in a single mode. An atom in a laser radiates by spontaneous emission. When it does that, it generates a photon. When the radiation from the laser is absorbed on a surface, for instance, the photons are destroyed. So the basic process of creating photons and destroying them is quite natural in light and part of the operation of a laser.

The idea of an atom laser seems absurd, because you cannot make atoms and you can’t destroy atoms either. So the title would seem to be a misnomer. But, in fact, it’s quite accurate. The atom laser was a product of the discovery of Bose-Einstein condensation in 1995, that’s Bose-Einstein condensation in atoms. In Bose-Einstein condensation the atoms in a system, instead of being in many, many different quantum states, are all in one state, and that’s the lowest energy state of the system.

The idea of a quantum computer was put forth many years ago by a great physicist Feinman, who pointed out that if you could make such a device, a quantum computer, you could simulate the behaviour of quantum systems which you couldn’t possibly compute otherwise. So this theme of quantum simulation is sort of the underlying theme of the current quest for quantum computers. Well, so the current theme of this field right now is quantum simulations, of building systems under such control that we can look at the behaviour of known Hamiltonians and study the behaviour of those Hamiltonians using the atomic system to simulate any other system which is governed by this Hamiltonian. There is great expectations that these simulations are going to totally change the way we understand matter. So this is a wonderful example of how physics leads from one area to another, and that ideas which seem totally absurd can come true.