Quantum computers take advantage of the behavior and properties of atoms to potentially provide switching and processing speeds millions of times faster than those of today's supercomputers. Line up a mere 50 qubits, and you could represent every binary number from zero to more than a trillion - simultaneously. Observation of a quantum computer allows an outside interference such as light or noise to exert some influence over the qubits, forcing them to collapse and leaving an ordinary computer based on ones and zeros. In order to allow quantum states to store information, a quantum computer can't interact with its environment. But at the same time, it has to be manipulated to allow calculations to be performed.
Reliability is a serious factor for quantum computers.
Calif. Quantum computers hold great promise in the area of cryptography. Qubits can't be copied or cloned, so it would be virtually impossible for a hacker to break code encrypted with a quantum computer. Carl Williams, a physicist at the National Institute of Standards and Technology in Gaithersburg, Md., and Umesh Vazirani, a professor of computer science at the University of California, Berkeley, say absolutely safe lines of communication will require a quantum repeater. A quantum repeater would allow the photon being transmitted over optical fiber to be repeated without being disturbed. The repeater would allow the photon to be transmitted another 50 km.