# Is decoherence continuous?

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1. Dec 3, 2014

### myki

When a particle decoheres, or its component states get entangled with the environment, surely this is not a final eigenstate. The particle is interacting ( becoming entangled etc) with other particles and systems constantly. Therefore, isn't decoherence a continuous process?

2. Dec 3, 2014

### VantagePoint72

Yes, decoherence is continuous. Dephasing (the type of decoherence that leads to classical behaviour and which is usually what people mean by decoherence) is the exponential (as a function of time) decay of the off diagonal terms in a density matrix. I'm not sure if that's what you mean, though. Are you asking whether the constant interaction means that a system might decohere and then recohere again? If that's your question, then no, generally not. The point is that dephasing is a reasonable model under all sorts of environmental interactions and, as I said, is a kind of exponential decay. So it tends toward a particular limit point (the full incoherent classical mixture state), it doesn't just kind of bounce around between a variety of totally different states.

3. Dec 3, 2014

### Staff: Mentor

Yes, as last man standing says, its continuous.

But I sense you may be worried about an issue that sometimes gets bought up in regard to it explaining apparent collapse. The interference terms get suppressed very quickly - but never actually become zero - simply way below our ability to detect. This is not the ideal state of affairs and is part of why its considered to resolve the measurement problem (not the major reason - but its certainly one of them) - For All Practical Purposes - but not totally resolve the issue.

Thanks
Bill

4. Dec 5, 2014

### myki

Thanks to Lastmanstanding and Bhoppa. I guess my rather naive question would then be: in a dense environment like the surface of earth, does that mean that, having all been measured by trillions of particles, do all particles in objects we observe remain permanently decohered? (notwithstanding undetectable interference terms washing about.)

5. Dec 6, 2014

### Staff: Mentor

Basically - yes. Only in some contrived situations like the double slit can you detect interference effects.

Thanks
Bill

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