Consider a collection of bombs, some of which are duds. The bombs are triggered by a single photon. Usable bombs will absorb the photon and detonate. Dud bombs will not absorb the photon. The problem is how to separate the usable bombs from the duds. ... A solution is for the sorter to use a mode of observation known as counterfactual measurement ... In 1994, Anton Zeilinger, Paul Kwiat, Harald Weinfurter, and Thomas Herzog actually performed an equivalent of the above experiment, proving interaction-free measurements are indeed possible.
Interesting.
See also:
Quantum interrogation by Sean Carroll
Interaction-free measurement (PDF) by Alan DeWeerd
As I understand it, the only way to have a known-live undetonated bomb in this branch is to cause it to actually detonate it in other branches.
Sorta, but not quite, as the probability of it actually detonating can be brought as close to 0 as one likes (if I’m not mistaken).
Yes—I didn’t mean all other branches.