What is entanglement purification and how does it work?

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I was hoping if someone could briefly explain entanglement purification. I’ve read http://www.lsr.ph.ic.ac.uk/~plenio/cp394311998.pdf , but because I’m not mathematically inclined most of it isn’t sinking in.

What I gather is in the beginning you share two entangled states, and one of the systems part of one entangled state is sent through a noisy quantum channel. This of course requires the use of a density operator (I gather in principle it is still in a pure state?), and so doing certain local actions allows one to teleport the state of another system onto the system sent through the quantum channel?

I gather this only successfully occurs some of the time. So it’s not that we create entanglement from one system being in superposition and coupling it to a system in a mixed (definite state), resulting in both systems being entangled? (can you even entangle two systems if any of its physical properties are in a definite state? Or entangle a certain physical property of two systems, if both systems are in a definite state in regards to that physical property)
 
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