They let it go and listen for the pop? Let it fall from the magnetic containment and you should see a predictable emission as it collides with some normal matter. Detecting single photons is what detectors are all about.
Sounds like that classic joke about a hunter finding his friend unconscious - the one where the dispatcher asks if the friend is dead…
This made me laugh very hard. Thank you.
I think this is a fascinating technology. I wonder if it is currently energy positive (so that we can engineer it into a functional source) or at least if it can be extended to be captured in bulk (antimatter rockets!).