Here too, however, there has been substantial recent progress. Shor is working on a method whereby each piece of information is spread, or entangled, over several qubits. In this way, the erroneous decay of one of the quantum states will not lose the information. Of course, using additional qubits trades off some efficiency. Shor's original scheme involved using nine qubits. More recently, Raymond Laflamme and his colleagues at Los Alamos National Laboratory have derived an error-correction technique that requires only five qubits. Shor is also studying how much error is allowable before it taints the results from quantum computers; in essence, proponents of quantum computing are trying to reinvent from the ground up all of the basic logic problems that other computer scientists have developed since the days of ENIAC, the ancestor of the modern electronic computer.
And the programmers working on ENIAC had a significant advantage over Shor and his ilk: they at least had a physical device to work with. Researchers at the National Institute of Standards and Technology, led by David J. Wineland, and a team headed by H. Jeff Kimble at the California Institute of Technology have made some headway in constructing real quantum systems that function as crude logic gates--sort of nano-transistors. These are only the first baby steps toward a full, workable quantum computer. (Click here to view a schematic of CIT's experimental setup.)
Nevertheless, many people are betting the technical hurdles are manageable. Researchers at M.I.T., Caltech and the University of Southern California have banded together to form the Quantum Information and Computing institute. The Defense Department's Advanced Research Projects Agency (ARPA) is providing a five-year, $5-million grant--a skinny slice of the total defense R&D pie, but a sign of faith that quantum computing will eventually find a place in our macroscopic lives.