In the context of atomic tunneling in an optical trap, it is indeed the atom's electron that is primarily involved in the tunneling process. In an optical trap, a tightly focused laser beam creates a potential energy well that can confine neutral atoms. The laser light interacts with the electrons in the atom, leading to the formation of a trapping potential.
When the atom is trapped in this potential well, its electronic wave function extends beyond the classical turning point of the potential barrier. This means that there is a finite probability for the electron to "tunnel" through the barrier and appear on the other side, outside the potential well.
The tunneling process can be detected by observing the scattered light. When the electron tunnels through the barrier, it may absorb some energy from the trapping laser and subsequently re-emit that energy as scattered light. By monitoring the scattered light, researchers can indirectly infer the occurrence of tunneling events.
While the atom as a whole is involved in the trapping process, it is primarily the electronic behavior that determines tunneling probabilities and is observed through the scattered light. The nucleus of the atom, being much more massive and localized, is less likely to participate in the tunneling process.