Atom Trap on a Chip

Researchers have developed a method of trapping clouds of atoms on the surface of a chip. The accomplishment is the first step toward an "atom chip" that could be the brain of a quantum computer, the superfast number cruncher some researchers are dreaming of.

Unlike ordinary computers that shuffle bits that are either 0 or 1, a quantum computer will use "qubits" that can be 0, 1, or 0-and-1 at the same time. Linked together, such qubits form a memory that can keep many different things in mind at the same time, enabling a quantum computer to do myriad calculations at once. Some researchers hope to fashion qubits out of individual atoms. But to do this, they will need chips that can guide tiny clouds of atoms along on their surfaces, rather like today's chips guiding tiny currents through microscopic circuits.

To trap and manipulate atoms on a surface, a team led by experimental physicist Jörg Schmiedmayer of the University of Innsbruck, Austria, etched tiny wires of two sizes into a gold layer covering a small gallium arsenide chip. The team then placed the chip in a vacuum chamber, where a combination of magnets and laser beams trapped a cloud of very cold lithium atoms and brought it close to the surface of the chip.

Then the external magnetic field and the lasers were turned off, and the currents in the thicker, 200-micrometer-wide chip wires were turned on to create a much smaller magnetic trap, thus compressing the atom cloud further. Finally, the thick wires were turned off and the thinnest, just 10-micrometers wide, were turned on, creating a tiny tubelike void in the magnetic field that trapped the atoms in an even smaller space, they report in the 15 May issue of Physical Review Letters.

The next step will be a chip in which you can move such tiny clouds along the wires, says Schmiedmayer, because to make a quantum memory, atoms have to be brought close to one another, so their quantum states link together or "entangle." Physicist Wolfgang Ketterle of the Massachusetts Institute of Technology says that the new technique constitutes "the first baby steps" toward such manipulation.

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