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Updated: Aug 8, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Inequalities and separations among assisted capacities of quantum channels
Charles H Bennett1, Igor Devetak, Peter W Shor
1IBM T.J. Watson Research Center, Yorktown Heights, New York 10598, USA. bennetc@watson.ibm.com
Abstract:
We exhibit quantum channels whose classical and quantum capacities, when assisted by classical feedback, exceed their unassisted classical Holevo capacity. These channels are designed to be noisy in a way that can be corrected with the help of the output and a reference system entangled with part of the input. A similar construction yields quantum channels whose classical capacity, when assisted by two-way classical communication independent of the source, exceeds their classical capacity assisted by feedback alone. We give a hierarchy of capacity inequalities and open questions.
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