And what they do is remarkable. Since one qubit can simultaneously represent two different values, two qubits can simultaneously represent four (00, 01, 10, and 11, in binary notation); four qubits can represent 16 values; eight qubits 256 values; and so on. Even a relatively small quantum computer, one that had a few tens of thousands of qubits, could consider so many different values at once that it would be able to break all known [ed: RSA, D&H, ECC, AES-128] codes commonly used for secure Internet communication. Quantum computers might also be used for faster database searches, or to tackle hard problems that classical computers couldn't solve with all the time in the universe. My colleagues at MIT and I have been building simple quantum computers and executing quantum algorithms since 1996, as have other scientists around the world. Quantum computers work as promised. If they can be scaled up, to thousands or tens of thousands of qubits from their current size of a dozen or so, watch out!

Given their power to intercept and disrupt secret communications, it is not surprising that quantum computers have the attention of various U.S. government agencies. The National Security Agency, which supports research in quantum computing, candidly declares that given its interest in keeping U.S. government communications secure, it is loath to see quantum computers built. On the other hand, if they can be built, then it wants to have the first one.