Creating perfect long-distance entanglement is extremely challenging and an almost impossible task. The quality of entanglement over a long distance will therefore hardly ever be 100% - which provides the motivation for needing an additional procedure: entanglement distillation. The entanglement distillation procedure works by combining multiple copies of weakly entangled states to obtain a smaller number of maximally entangled pairs.

Entanglement distillation is the transformation of N copies of an arbitrary entangled state into some number of approximately pure Bell pairs, using only local operations and classical communication (LOCC). Quantum entanglement distillation can in this way overcome the degenerative influence of noisy quantum channels by transforming previously shared less entangled pairs into a smaller number of maximally entangled pairs.

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