What Causes Decoherence in Quantum Systems?

[bluecap]

Let me be a little clearer here. To me, decoherence means entanglement between a system and its environment. If you have two microscopic systems that are entangled, decoherence can possibly destroy that entanglement, but it does this by creating new entanglements with the environment.

Even in eigenstates of positions, the quantum nature is never suspended. So for example a painting like Mona Lisa. Can you shine some lasers into it to change the drawing not by erasing the canvas and repainting with hands but by entangling it with a new measuring device? What would it take (what kind of device) can change the the eigenstates of positions of the paint pigments. Or it's better to use an example of sculptures like those from http://artistsinspireartists.com/sculpture/famous-sculptures-world
In the first example of sculpture called David created by Michelangelo in 1501 – 1504 located Galleria dell’Accademia, Florence, Italy. What kind of instrument can you use to make it create new entanglement with the sculpture such that you can change the face to another person like your face without using chisel.. then the next day changing back the face to David? If we don't have the technology yet. Is it theoretically possible say come 100 Billion A.D.? or forever impossible?

 

[David Lewis]

If there is a single atom whose decay triggers the death of the cat, then what's really going on is that atom's state is becoming entangled with that of the cat and the rest of the universe.

Very true, but there is a time when the radioactive atom is neither decayed nor undecayed, but a superposition of both.

 

[jartsa]

Decoherence as I understand it simply is entanglement with the "environment".

If an electron is in a superposition of spin-up and spin-down states, and a measuring device measures that electron's spin, what decohores? Electron? Device? Electron-device-system? My answer is device.

If somebody is trying to show that the electron is in a superposition of the two states, after the electron has gone through the spin-measurer, but before all information about the result of the measurement is wiped out, that person will fail.

And that is a huge problem, because of relativity of simultaneity.

The many worlds interpretation solves that problem by saying that the electron did not react in any way to the wiping of information far away. So the electron was the same all the time.

When a photon goes through a double slit screen, the photon gains some information about the environment.
When an electron goes through a spin measurer, the electron does not gain information about the environment.

EDIT: My spin-measurer was just a loop of wire and a sensitive ammeter, not a Stern-Gerlach-device. I hope my device does not disturb the electron's path.