Explicit channels with unbounded gains in classical communication using entangled inputs

Abstract:We construct an explicit family of finite-dimensional quantum channels for which the optimal classical communication rate achievable with product-state codewords and collective decoding tends to zero, while rates achievable using entanglement only within pairs of channel inputs grow without bound. Our construction combines deterministic qudit Clifford unitaries with a binary measurement and classical feedforward, providing a derandomization to Hastings' probabilistic construction. The key ingredient is a careful design of measurement and feedforward process that yields the required one-copy and two-copy output entropy bounds from moment estimates alone, without requiring strong convergence of the underlying unitary family.

Quantum Physics (quant-ph); Information Theory (cs.IT); Mathematical Physics (math-ph)

arXiv:2609.26743 [quant-ph]

(or arXiv:2609.26743v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2609.26743 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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