Paul Boxley

How long until we have quantum computers?

Scott Aaronson on why we don't yet have quantum computers:

The central technological obstacle to building a scalable quantum computer is well-known, and is decoherence, or unwanted interaction between the computer and its external environment. When information about a quantum state leaks into the outside world—by any means whatsoever, intended or not—the state loses its “quantumness” and reverts to being classical. So to do a quantum computation, it’s necessary to keep the qubits (atomic nuclei, photons, or whatever else they are) almost fanatically isolated from their environment. But at the same time, you also need to manipulate the qubits, move them around, etc., in such a way as to carry out the computation. Those twin requirements are the reasons why the most famous ’success’ of practical quantum computing to date was factoring 15 into 3×5.