Attempts to build quantum computers could run up against a fundamental limit on how long useful information can persist inside them. Exceed the limit and information could just leak away, making computation impossible.
A quantum computer manipulates stored information in quantum bits, or qubits. Because a qubit can be in twostates at the same time, and can be entangled with other qubits, a quantum computer can carry out multiple calculations simultaneously.
Read the complete story. (New Scientist)