# Entangled Photons

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1. Feb 5, 2016

### MaxwellDemon

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? And can two entangled photons combine into one?

2. Feb 5, 2016

### zonde

No. Otherwise we wouldn't be able to perform Bell experiments with photons (not even mentioning that it would allow FTL communication).

3. Feb 5, 2016

### vanhees71

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).

4. Feb 5, 2016