Quantum Leap: Seize the Light These days, quantum computers are scrawny little gadgets whose greatest accomplishment so far is factoring the number 15.
However, their power grows exponentially with size, so whenever quantum computers grow a little bigger, researchers get more than a little excited.
Two papers this month, in fact, present new frameworks for quantum information storage and large-scale quantum computation -- involving hundreds of thousands of potential quantum bits (qubits). Both tasks are essential to making a quantum computer, and both entail challenges for the engineer as well as the theoris
One system involves a new state of matter called either a "Mott insulator" or, more colloquially, a "patterned liquid." The other concerns a method of stopping, storing and retrieving light pulses, as if they were an atom, or a carton of milk that could just be thrown in the refrigerator.

This week, a team of physicists at Munich's Max Planck Institute for Quantum Optics and Zurich's Institute of Quantum Electronics published a paper in Nature in which they cooled and cajoled a gas of rubidium atoms into an orderly grid framework. Each grid element is filled with one and only one atom, and each atom can be individually manipulated via finely tuned magnetic pulses.

"One way to picture this new state of matter is as an egg carton which is filled with eggs," Immanuel Bloch of the Max Planck Institute said. "The 'eggs' in our case are individual atoms, and the 'egg carton' is formed by a crystal of light."

Crisscrossing beams of lasers form a crystal-like structure that defines the boundaries of each atom's confined space, like the contoured cardboard of an egg carton. And the cool temperatures (less than a hundred-millionth of a degree above absolute zero) keep the atoms from fidgeting out of their assigned seats.

"The (Mott insulator) phase, by its nature, wants to have every atom as an individual atom," Henk Stoof of the University of Utrecht in the Netherlands said. "They don't interact with each other. So it's not something you have to struggle against."

Bloch and his team were able to maintain this high state of order over a network containing some 150,000 rubidium atoms. Each atom acts like a miniature bar magnet that can point up ("1") or down ("0") -- or, in the case of a qubit, weird intermediate quantum states of both up and down at the same time.

Since each atom sits alone and unperturbed, each atom is free to carry out the steps of a quantum algorithm -- which requires that no stray atoms, electrons or photons bounce off it and upset its delicate work in progress.

The difficult task ahead is developing the quantum logic gates to lead these qubits through a calculation. Then, of course, one must also figure out a way to read the results of a computation once it's completed.

Bloch's team has ideas for clearing both hurdles -- involving pulses like those used in NMR machines -- but this work is still underway.

While Bloch and other researchers around the world contemplate Mott insulators as the ultimate quantum computer processors, another group has tackled the quantum RAM question.

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