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Science in Focus: Matthew Walhout

Science Highlights of 2012, Part 1

Captivating developments in quantum physics.

These are remarkable days in atomic, molecular, and optical (AMO) physics, a scientific sub-discipline that counts two more of its own as Nobel laureates this year. The honorees, Frenchman Serge Haroche and American David Wineland, rank among a vanguard of experimenters who have developed powerful techniques for studying the world of tiny objects, or the quantum world. This is the domain where molecules, atoms, and the "subatomic zoo" of even smaller particles behave in outlandish ways, and where scientists have to rely on the strange theory of quantum mechanics in order to describe and predict that behavior. Key laboratory innovations have moved AMO physicists beyond the project of merely mapping the quantum world. The ambitious new goal is to harness and exploit the riches that can be found there.

This movement relies on a methodology that may seem counterintuitive to casual readers of popular science. According to one line of traditional wisdom, unlocking quantum secrets requires high-speed "atom smashing" at specialized particle colliders. Indeed, this strategy has proven itself many times over. Its most recent triumph made headlines in July, when scientists at CERN announced that they have tracked down their most elusive quarry, a particle known as the Higgs boson. But the path of violence is not the only avenue into the quantum world. There is a gentler approach. Rather than building systems that pack a more destructive punch, the new pioneers of AMO physics have tried to minimize the effects of collisions. They prefer decelerators to accelerators, because their strategy is to capture and hold onto individual particles for long periods of time. This approach enables them to perform extended measurements and to exert precise control over each particle's quantum properties.

Prizewinners Haroche and Wineland have spearheaded key experiments on trapped particles, but their individual projects are conceptual inverses of each other. Wineland traps ions (electrically charged atoms) and shines laser light on them in order to detect or modify their quantum properties. Haroche captures photons (particles of light) and sends atoms into the trap in order to probe the "photonic state," or the quantum-mechanical profile of the confined light. Wineland's trap is made of electric and magnetic fields; Haroche's is a pair of mirrors.

Matter and light interact placidly in these experiments. Comparing this interaction with what happens in particle accelerators is like comparing the trickle of a drinking fountain with Niagara Falls. Everything is much more manageable and orderly in the trapped-particle systems. What may be most important—at least from a technological standpoint—is that the delicate property known as quantum information can be preserved and manipulated. Control over this property could make it possible for particle trappers to build quantum-information processors that will have unprecedented computing power. It should be no surprise that the 2012 Nobelists and a growing posse of other AMO physicists are actively scouting out this futuristic notion.

To a large extent, the AMO renaissance of the last three decades has been fueled by an attraction toward intriguing technological possibilities. But more generally, it has resulted from a change of mindset regarding the goals of research. Few physicists these days spend their time exploring and documenting the unique characteristics of hydrogen, helium, or any other specific kind of atom. Instead the trend is to treat every atom as a potential carrier of generic quantum properties (such as information). The primary focus is not on the particles themselves but on how they can be used in the quest to learn or do interesting things. Consequently, AMO physicists do far less cataloguing now than in days past, but they do far more of what might be called quantum engineering. Their innovations are coming at a faster pace than ever, and this year's Nobel Prize will certainly not be the last to be awarded in this exciting field of research.

AMO physicist Matthew Walhout is professor of physics and dean for research and scholarship at Calvin College.

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