The discussion revolves around the behavior of entangled photons, specifically what occurs to photon B if photon A is destroyed and whether two entangled photons can combine into one. The scope includes theoretical implications of entanglement and measurement in quantum mechanics.
Participants generally agree that photon B is not destroyed if photon A is destroyed, but there are differing views on the implications of measurement and the nature of the polarization states involved.
The discussion includes assumptions about the measurement process and the definitions of polarization states, which may not be universally agreed upon. The implications of entanglement and measurement are complex and not fully resolved in the conversation.
No. Otherwise we wouldn't be able to perform Bell experiments with photons (not even mentioning that it would allow FTL communication).MaxwellDemon said:If a photon A is entangled with photon B and one somehow destroys photon A, what will happen to photon B? Will it also get destroyed?
vanhees71 said:If the two photons are detected at well separated places and you make sure that A has absorbed only 1 of the two photons, nothing happens to the other photon. As long as A doesn't take notice of the polarization state (I guess you talk about the usual polarization-entangled two-photon states used in Bell experiments), B's photon will be completely unpolarized, i.e., its polarization state is described by the statistical operator ##\hat{\rho}=1/2 \hat{1}##.
If, however A has measured the polarization state of her photon, she knows that B will find the photon in the perpendicular polarization (if B measures in the same polarization direction), i.e., then she'd associate the corresponding pure polarization state with B's photon. If, however, she hasn't B told her result, B will just not now, what he will measure and thus will simply get a random polarization result (with probability 1/2 horizontal and with probability 1/2 vertical polarization).