- TL;DR Summary
- Quantum information seems to be lost in a thought experiment involving absorption of photons
Suppose I fire a photon with an upward spin towards a hydrogen atom. It is absorbed by the hydrogen atom's electron which subsequently emits a photon when it returns to its ground state. I then fire another photon with a downward spin towards the same hydrogen atom and the same thing happens. Is it possible to deduce the spins of the original photons by measuring the emitted photons and the hydrogen atom? If not, is information lost?