[katieHaylor (OP)]

Tilo asks:

Is it possible to determine the spin of an entangled photon, respectively of an entangled quantum pair, before direct measurement? For instance using a second entangled photon pair or a single photon with known spin for an indirect measurement?

For example, I'm thinking about a particle channel within a particle trap. The characteristics of the individual particles are known. Suppose we send an entangled photon through this channel, and afterwards we measure the particles out of the particle channel regarding the change of characteristics. Is any indirect/contactless transfer of information possible?

What do you think?

[evan_au]

One of the common ways to generate entangled photons starts with a laser beam.
The entangled photons produced by this process inherit some characteristics of a laser beam.
Unfortunately, high intensity isn't one of them.
And you can't use Light Amplification by Stimulated Emission of Ratiation (acronym: LASER) to amplify the entangled photons, because each time an entangled photon interacts with a particle in the laser cavity, it will lose coherence with its entangled partner.
https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion