Universal Improvement of Channel Fidelity via Entanglement AssistanceResearch Paper
Motivation
Communication using quantum channels generally requires encoding and decoding on many identical uses of a quantum channel. In practical settings, decoherence may severely limit our ability to do so, potentially rendering each channel use nonidentical. Given nonidentical channels, we present an entanglement-assisted encoding and decoding strategy that yields a channel with higher worst-case fidelity than all of the given channels. The strategy is universal, in the sense that the improvement holds regardless of what channels are given, as long as they satisfy mild assumptions on their initial entanglement fidelities. Our protocol is optimal when the given channels are depolarizing channels, and is essentially the unique one that is universal. This idea can also be extended to classical channels, where shared randomness between the sender and the receiver allows universal enhancement of the probability of correct transmission. We then consider general quantum resource theories, providing a necessary condition and a sufficient condition for the possibility of such universal improvement of quantum resources. △ Less
This mission is the statement-level formalization of Universal Improvement of Channel Fidelity via Entanglement Assistance (arXiv:2610.05669v1). Every numbered result of the paper was scanned. The results stated here are open sorry goals, ready for solvers to prove.
What is formalized
7 statements of the paper are in Lean 4 (Mathlib 0df444a). The goal theorem is Unnumbered: shared-randomness protocol and identity-biased improvement (Unnumbered: shared-randomness protocol and identity-biased improvement, PDF p. 6). The milestones are the other numbered results, in the paper's order, each quoting the paper.
The paper's own objects are the definition item of this mission. Objects shared across papers come from the prove2quantum library and from earlier papers' missions, listed as references.
Provenance: prove2quantum's pipeline drafted each statement (gpt-6.1-sol on Stanford's Sherlock cluster). A blind read-back, written without seeing the paper, is attached to every item. An independent moderator compared each statement against the paper and passed the whole paper without edits.
Deferred results
25 results of the paper are not stated yet, because the library lacks an interface they need:
- Theorem 1: universal entanglement-assisted improvement: Explicit n-register entanglement-assisted Bell agreement instrument, its local separated-party realization, and reference-assisted worst-case squared fidelity. (hard)
- Unnumbered: untwirled entanglement-assisted protocol, Eqs.15–22: Concrete raw Bell-agreement instrument with N-tensor-id weights and transpose corrections. (hard)
- Proposition 2: optimal fidelity upper bound for generalized Pauli inputs: Heralded NS-assisted superinstrument predicate retaining both no-signalling marginals and action on arbitrary input maps. (hard)
- Unnumbered corollary: optimal depolarizing fidelity and single-use obstruction: Heralded NS model and the concrete EA construction, parameterized by entanglement fidelity rather than depolarizing noise rate. (hard)
- Proposition 3: optimal success probability at optimal two-channel fidelity: Heralded NS model, exact optimal-output fidelity, and input-independent success scalar on strict interior depolarizing inputs. (hard)
- Proposition 4: uniqueness of the universal quantum protocol: NS instrument plus supermap input/output Haar twirls and explicit twirled EA branch. (hard)
- Proposition 5: classical NS fidelity upper bound: NS instrument on classical embeddings, classical minimum-diagonal fidelity and the extended column ratio. (hard)
- Unnumbered corollary: optimal d-ary symmetric fidelity: NS-assisted upper bound and achievable fully specified shared-randomness instrument on symmetric inputs. (hard)
- Proposition 6: uniqueness of the universal classical protocol: NS instrument and equality of fully classically twirled supermaps with the SR successful branch. (hard)
- Unnumbered example: two entanglement-breaking channels yield a non-breaking output: Physical EA Bell construction joined to the accepted finite-dimensional entanglement-breaking predicate. (hard)
- Theorem 7: sufficient conditions for universal resource distillation: Theorem 7: sufficient conditions for universal resource distillation; source domain/provenance (source-ambiguity)
- Proposition 8: multiplicativity from product-generated free sets: A paper-local generalized channel twirl and compatible one-system and two-system free-channel sets, including convex-hull and affine-hull-within-CPTP product generation. (hard)
- Theorem 9: generic uniqueness up to twirls and rescaling: Theorem 9: generic uniqueness up to twirls and rescaling; source domain/provenance (source-ambiguity)
- Theorem 10: obstructions to universal resource distillation: Theorem 10: obstructions to universal resource distillation; source domain/provenance (source-ambiguity)
- Theorem 11 [22, Thm.1]: Choi representation of completely CPP supermaps: Theorem 11 [22, Thm.1]: Choi representation of completely CPP supermaps; source domain/provenance (hard)
- Unnumbered supplementary result: output twirling makes success state-independent: Twirling of a whole physical superinstrument and its conditional reference-assisted fidelity functional. (hard)
- Lemma 1: robustness equality and the free isotropic interval: Lemma 1: robustness equality and the free isotropic interval; source domain/provenance (source-ambiguity)
- Background: capacity and one-shot coding results: Background: capacity and one-shot coding results; source domain/provenance (hard)
- Background: process-tomography query lower bound: Background: process-tomography query lower bound; source domain/provenance (hard)
- Background: universal purification no-go results: Background: universal purification no-go results; source domain/provenance (hard)
- Background: realization, NS/RNG equivalence and generalized twirl realization: Background: realization, NS/RNG equivalence and generalized twirl realization; source domain/provenance (hard)
- Background: Haar twirling and entanglement-breaking depolarizing criterion: Background: Haar twirling and entanglement-breaking depolarizing criterion; source domain/provenance (hard)
- Background: static projective robustness conversion criteria: Background: static projective robustness conversion criteria; source domain/provenance (hard)
- Background: resource-theory examples with free twirls or equal robustness: Background: resource-theory examples with free twirls or equal robustness; source domain/provenance (hard)
- Background: open-to-closed threshold universality step: Background: open-to-closed threshold universality step; source domain/provenance (hard)
Selected references
- Universal Improvement of Channel Fidelity via Entanglement Assistance, arXiv:2610.05669v1, https://arxiv.org/abs/2610.05669v1