Quantum net for atom anglingPhysicists should be able to land exact numbers of atoms from a quantum cloud.30 July 2002
Scientists should be able to fish out an exact number of atoms from puddles of many thousands using a quantum net, new calculations suggest1. The size of the catch, say Roberto Diener and colleagues at the University of Texas at Austin, will depend on how fast they yank the net out of the atom pool. This will influence how easily atoms in it can wriggle back into the pool. The puddles in question are Bose-Einstein condensates (BEC) - clouds of atoms that behave as though they were a single super-atom. BECs form only at very low temperatures, in a gas of atoms held by electrical or magnetic forces in an atom trap. The net is a quantum dot - a piece of material so small that its properties, which are governed by the laws of quantum mechanics, depend on its size. A typical quantum dot might be a particle of a semiconductor or metal just a few millionths of a millimetre across. The dot attracts atoms. Plunged into a BEC, the dot is like a tiny well in the bottom of the broad pond in which the BEC is trapped. As the dot is pulled out of the trap, any atoms that are stuck in it will tend to escape back into the pond, the researchers predict. But because the movement of atoms between the dot and the pond is controlled by quantum mechanics, they should show some unusual behaviour. If the dot were withdrawn very slowly, all of the atoms stuck in it would leak away. If it were pulled out infinitely fast, none of them would have a chance to drain away. Between these two extremes, the number of atoms left in the dot will be highly sensitive to how fast it is reeled in. Diener and colleagues show that within a certain range of speeds, only one atom will stay on the dot. At faster speeds there should be a sharp switch to the situation in which two atoms remain - and so on. BEC and call Physicists have gone fishing for atoms before. For the last decade they have been picking up atoms of various elements off the surfaces of solids one by one with a device called a scanning tunnelling microscope. This has even been used to write and draw pictures at the atomic scale by arranging atoms on a surface.
But Diener's team are the first to show how to pluck atoms individually from a BEC, where they display wave-like behaviour. The atoms hooked by the quantum dot remain in an interdependent quantum state, like a tiny droplet of a Bose-Einstein condensate. Manipulating BECs is important for developing quantum computers, which should be far more powerful than today's ones. Last year physicists figured out how to guide a BEC hovering over the surface of a microchip2. The new work lends a delicate touch to this sort of manipulation. | |||||||||
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