Classical capacity

Construct a simple closed-form or practically computable counterexample to additivity of the Holevo capacity or the entanglement of formation, together with a rigorous certificate of a strict violation.

• Quantum Communication
• Quantum Resource Theory
• Classical capacity
• Additivity and regularization
• Entanglement measures

Can Holevo–Schumacher–Westmoreland codebooks operating at every rate below their ensemble Holevo information be chosen so that their square-root, or pretty-good, measurements have uniform quantum implementations whose cost is polynomial in the blocklength and…

• Quantum algorithm
• Quantum Communication
• Decoding algorithms
• Classical capacity
• Quantum state discrimination

Does the pure-loss bosonic channel admit the following candidate second-order classical converse under a maximum-photon-number occupation constraint?

• Quantum Communication
• Bosonic channels
• Classical capacity
• One-shot and finite-blocklength bounds

Characterize the finite-dimensional quantum channels for which joint classical–entanglement coding strictly outperforms time sharing between unassisted and unlimited-entanglement classical communication.

• Quantum Communication
• Quantum Resource Theory
• Classical capacity
• Entanglement-assisted communication
• Additivity and regularization