And the only way to interact with parallel universes is if they are totally identical except what's inside of the quantum computer itself. Deutsch posits that the quantum computer essentially proves many-worlds.
"The natural computational abilities of reality itself"
Additionally you continue to insist that computation is a real physical thing. Are you claiming that nature is aware of the states we assign it to perform computation?
The way computation works is that we map various physical states with our own semantic abstractions. I can change the computation for addition into one for subtraction without any physical change to the system. So there is no harnessing of "the natural computational abilities of reality itself". We merely observe natural behavior and semantically map it (which is what engineering is).
You can create a computing machine by assigning physical states to any physical behavior, quantum, classical, hamiltonian, etc. The proof is trivial and it is not a proof he came up with.
It further follows, there is no computation happening during the creation of an interference pattern until we assign it our own abstract semantic states.
This quantum woo is helping neither science nor quantum physics; in fact you are hindering it. Ascribing causal responsibility to non-observable (explicitly unknowable)† entities used to be criticized as dogmatic dribble, now it's embraced as popular science meant only to provoke reaction. Science is about establishing useful models of the world to make physical predictions.
† See common fallacy: https://en.wikipedia.org/wiki/Ontological_argument
All of science is abstract, not even "force" describes something physical. There are many more concrete models like Bohmian that don't rely on unprovable conjecture.
So does religion, it doesn't make it true without evidence. Inventing unseen universes is easy, it's not simple, it fails the Occam's razor test for the same reason gods do.
Second, since when is one atom responsible for a computation? In modern electronics no atom is responsible at all for computation, only the electrons are†. Even then, computation is an emergent property, computation itself is abstract and cannot be physical; but it emerges from physical interactions.
† Not even the electrons are directly, it's the energy propagated by the electrons!Hence why electronics are instant while the speed of an electron is a few cm a second