SPDC & Entanglement: Downconvert for 3 Particle Entanglement?

[entropy1]

Is it possible to downconvert an entangled photon and could that mean three particles get entangled and why not?

Thanks! :)

 

[DrChinese]

Is it possible to downconvert an entangled photon and could that mean three particles get entangled and why not?

Thanks! :)

I have never heard of 3 photons directly coming out of down conversion. However, sometimes you can get 4 that are entangled. That is 2 sets of 2, which happens sometimes with PDC. Once you intercept 1, the other 3 are then entangled. This technique is used for GHZ tests.

https://arxiv.org/abs/quant-ph/9810035

On the other hand: you can get 3 entangled photons from other sources.

https://arxiv.org/abs/1510.05898

 

[Cthugha]

Yes, you can do that using cascaded SPDC crystals:
Direct generation of photon triplets using cascaded photon-pair sources

However, you end up with photons at different energies which renders it tricky to perform experiments. Still, things such as polarization entanglement are possible:
Direct generation of three-photon polarization entanglement