From: "Patrick Leahy"
> NB: I'm in some terminological difficulty because I personally *define*
> different branches of the wave function by the property of being fully
> decoherent. Hence reference to "micro-branches" or "micro-histories" for
> cases where you *can* get interference.

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Do you agree we can have branches (or histories) in space
(in a space) but also branches (or histories) in time?
You have an atom, excited (ie by a laser).
This atom can radiate a photon in two different
ways (I mean two different transitions), having
the same life-time. Of course the photon has
the energy E1, or the (different) energy E2.
You can write the amplitude as ....
[a exp(-iE1 t/h) + b exp(-iE2 t/h)] e^(-k t)
The probability, for a transition to occur,
at a specific time, with emission of one photon
(it does not matter, here, if its energy is E1 or E2),
is given by two terms, plus an interference term.
You can, of course, introduce decoherence in this sort
of 'interference in time' quantum experiment (quantum
beat), by filtering for energies, ie for E1 or for E2.
In that case the extra interference term disappears.
-serafino