Extension of universal entanglement distillation to non-i.i.d. sources

Determine how far the universal achievability of distillable entanglement under LOCC can be extended from i.i.d. input states to non-i.i.d. input sources.

Background

The paper establishes that the distillable entanglement of an arbitrary unknown bipartite state can be achieved by a fixed, state-agnostic LOCC protocol when the parties receive i.i.d. copies of the input state. The construction relies on state tomography, perturbation to full-rank states, uniform convergence of finite-block quantities, and universal state merging for compound inputs.

The conclusion explicitly identifies extension beyond the i.i.d. assumption as an unresolved question. Such an extension would determine whether the operational meaning of distillable entanglement under universal, state-agnostic protocols persists for more general correlated or otherwise non-i.i.d. quantum sources.