> Therefore interaction by itself does not cause decoherence.
If you *encode* the "welcher weg" information
you get decoherence.
- Schneider, LaPuma, Am. J. Phys., 70 (2002) 266
Leonard Mandel put it in the strongest way:
"The mere possibility, in principle, of performing
the auxiliary measurement is sufficient to
destroy the interference. The quantum state
in this case is in the form of a diagonal
density operator which reflects what is
knowable, in principle, rather than what
Found. Phys., 25 (1995) 211
About the (finite) information involved, see also