Decoherence

There is a sense in which simple interference effects are destroyed when a system's environment becomes correlated with its state. This phenomenon is called decoherence. I shall consider three approaches here. According to one, decoherence alone explains why we get determinate records. According to another, decoherence helps one to formulate a satisfactory interpretation of Everett by selecting a globally preferred basis that makes the right physical facts determinate in each Everett branch. According to a third, decoherence sects a locally preferred basis for each observer that makes the right physical facts determinate from the perspective of that particular observer.

We have already alluded to decoherence in connection with the emergence of classical space-time, the ‘collapse′ of the wave function (Case 3) and the notion of entanglement. Physicists have hailed the discovery of decoherence as ‘the most important advance in the foundation of quantum theory since Bell's inequalities.’¹³¹ This praise is based on good reasons: (a) decoherence offers new ways of understanding quantum mechanics for it embodies a critique of entrenched terminology (‘collapse’ of the wave function, complementarity); (b) it is testable since it appeals to physical processes; (c) it offers an insight into a much more fundamental level of quantum indeterminacy.

A detailed investigation of decoherence during gating due to a bosonic environment was performed in the original work of Loss and DiVincenzo. Since then, there have been many studies of leakage and decoherence in the context of the quantum-dot quantum computing proposal.

One way of preventing both decoherences is to set up the system in a "non-decoherent quantum state."