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Yet a truly useful quantum computer will need hundreds or even thousands of qubits. Presumably, says Chuang, that means some kind of long-chain polymer. But developing the right kind of polymer, figuring out how to stabilize it, and then learning how to do NMR with it-that all adds up to many more years of research. And that’s if NMR is the final answer for quantum computing-a prospect that is no more guaranteed than that vacuum tubes were the final answer for conventional electronic computers. Ultimately, a practical quantum device might take some other form entirely. In the “ion trap” approach, for example, the qubits are ionized atoms suspended in an oscillating electric field. This approach has proved fiendishly difficult to implement, despite some preliminary success by physicist Christopher R. Monroe and his team at the National Institute of Standards and Technology in Boulder, Colo. But if the ion trap idea ever pans out, it will be a remarkably clean and elegant system to program. Alternatively, there are “quantum dots” in which the qubits would be electrons trapped in an array of tiny structures etched onto the surface of a silicon crystal (see ” Quantum Dot Com,” TR January/February 2000). Then there is the liquid crystal approach, the crystal lattice approach-on and on.

The myriad possibilities are limited only by your imagination, says Gershenfeld-which is precisely why quantum computing has stirred up so much excitement. “This has the feel of being a whole new science,” he declares. “Computer scientists are having to learn physics, and that doesn’t quite fit into their intellectual framework. Physicists are having to learn computer science, and that doesn’t quite fit into their framework. Quantum computing breaks down the institutional boundaries at almost any institution you can name. And every side is the richer for learning a new language for describing the world.”

But perhaps an even deeper reason for the excitement is the way quantum computing expands our intellectual horizons. “I’m not just doing this for the sake of quantum computing,” says Chuang. “I’m doing it because so little is known about computing in general. For 50 years we’ve just focused on one technique in computing”: that is, microchips based on the on-off dichotomy of binary logic. The pursuit of quantum computing, Chuang believes, addresses a fundamental issue: “What does it take to perform a computation-and how can we manipulate nature’s laws to perform the computation we want? That is the more basic question that quantum computing brings out.”

On the Quantum Quest Organization Key Researchers Focus IBM/MIT/Berkeley/Stanford Isaac Chuang (IBM)
Neil Gershenfeld (MIT) “Enabling technology” for NMR-based quantum computing; scale up to 10-40 qubits Harvard/MIT/Los Alamos David Cory (Harvard) Quantum algorithms and NMR-based systems NIST Christopher R. Monroe Ion-trap quantum computing; demonstrated a two-qubit device using trapped barium ions Caltech/MIT/USC Seth Lloyd (MIT)
M. Despain (USC)
H. Jeff Kimble, John Preskill, and Steven Koonin (Caltech) Algorithms and quantum error correction Oxford University David Deutsch, Jonathan Jones Ion-trap and NMR implementations; quantum information theory

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