More is Different

The quantum protectorate describes a stable state of matter whose generic properties are determined by a higher organising principle and nothing else. The very large number of atoms present in real bits of matter lead to fundamentally new types of behaviour which are not just simply the properties of an individual atom multiplied by the number of atoms. Different behaviour occurs when you have more.

The challenge is that a large-scale quantum machine must, by definition, operate in the quantum realm, and yet when we try to build one large enough to be useful, its natural tendency is to start obeying the classical rules of the macroscopic realm.

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