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Physical Review Letters 83, 3566–3569. Original account of entanglement catalysis by Daniel Jonathan and Martin B. Plenio.

Author preprint: arxiv.org/abs/quant-ph/9905071

Martin Bodo Plenio and Daniel Jonathan showed that a shared auxiliary entangled state can enable a deterministic LOCC conversion that is impossible for the original pair of pure quantum states alone. The auxiliary quantum state is returned unchanged and uncorrelated with the output, so it acts as a catalyst for entanglement catalysis. The key distinction is between consuming an extra resource and using one that can be recovered: a majorization obstruction for the original Schmidt coefficients can disappear after including the catalyst's Schmidt coefficients.^[ref]