= Reliable quantum source compression
A quantum source-compression scheme has encoding and decoding <quantum channels> with compressed space $\mathcal K_n$ and rate $\limsup_n n^{-1}\log_2\dim\mathcal K_n$. For a pure-state source ensemble, average reliability means that the mean squared <quantum fidelity> after decoding tends to one. A stronger coherent criterion is $F_e(\pi^{\otimes n},\mathcal D_n\circ\mathcal E_n)\to1$, where <entanglement fidelity> also tests a purification reference. Encoding the <quantum typical subspace> achieves both criteria above $S(\pi)$. https://doi.org/10.1103/PhysRevA.51.2738[Schumacher's original quantum coding paper] establishes quantum source coding.
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