Quantum computers are a very special breed of computer that depend on the superposition and entanglement of quantum states. Computer components are getting smaller all the time, and no doubt they will eventually reach the nano-scale where quantum effects start to play a part. But this alone will not make them quantum computers. They will still work pretty much like an ordinary PC, and be able to solve the same limited kind of problems.
True quantum computers have the potential to solve much more demanding problems because they can exploit the quantum coherence that results from the wave nature of quantum systems. This coherence means that the basic processing components of a quantum computer have a common phase – just like the photons in a laser beam. A classical memory register that has N bits, each of which can be in one of two states 0 and 1, can store any one of 2N configurations at a given time. However, a quantum-coherent register that contains N quantum bits, or qubits, can store a coherent superposition of all 2N configurations at the same time.
But therein lies the problem of actually building a quantum computer.
In the May issue of Physics World, Goran Wendin from the Department of Microtechnology and Nanoscience at Chalmers Institute of Technology in Sweden describes how solid-state quantum information processing has moved a step closer thanks to macroscopic circuits that behave like single quantum objects.
