A Note on the Question of Scaling: Decoherence and Error Correction

Demonstrations of principle, such as a quantum gate with a single spin or ion or the realisation of entanglement in various physical situations, constitute first steps towards quantum information processing that require up- or down-scaling to achieve effective processing of quantum information. Decoherence makes increasingly difficult the up-scaling of quantum information systems to a few spins or ions. This process destroys the correlations among the individual spins or ions, losing quantum information into the environment and introducing errors in any QIP routine.